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Question 1 of 17
1. Question
Structural characterization of scorpion peptides and their bactericidal activity against clinical isolates of multidrug-resistant bacteria
(1) Scorpions are arthropods belonging to the group of arachnids, which have lived on our planet for more than 400 million years. Currently, approximately 1500 species of scorpions have been described, and the study of their venoms has resulted in the discovery of a large arsenal of bioactive molecules; among these molecules, toxins are distinguished by their ability to modulate the function of diverse ion channels and membrane receptors, causing the symptoms of poisoning. Other interesting biomolecules that have been discovered in scorpion venoms are antimicrobial peptides (AMPs), which stand out for their broad-spectrum activity against Gram-positive and Gram-negative bacteria, fungi, yeast, and protozoa. The most interesting AMPs from scorpion venoms are those falling out of the Buthidae family, which do not present any risk to human health; the venoms contain antimicrobial peptides (AMPs) involved in the innate immune response of venomous arthropods. Scorpion AMPs also function as internal immune agents protecting the venom gland from infection and external immune agents cleaning saprophytic microbes from the surface of the scorpion body. In addition, synergistic effects of antimicrobial scorpion peptide and neurotoxins against bacteria has been described, which provides further evidence in favor of the multifunctionality of scorpion venom components. Most of these antimicrobial peptides do not contain disulfide bridges in their structure, known as non-disulfide-bridged peptides (NDBP), and have been classified into several groups, such as scorpine-like, long, intermediate and short-chain AMPs.
(2) Scorpine-like AMPs possess two structural and functional domains: a N-terminal α-helix (with cytolytic and/or antimicrobial activity like the insect defensins) and a tightly folded C-terminal region with a CSαβ motif, displaying K+ channel-blocking activity. The first characterized scorpine was isolated from the venom of the scorpion Pandinus imperator. This protein is formed by 75 amino acids and has shown antimicrobial activity, mainly against Bacillus subtilis, although it also has an inhibitory effect on the ookinete and gamete stages of Plasmodium berghei.
(3) Long-chain AMPs, such as hadrurin (isolated from Mexican scorpion Hadrurus aztecus), belong to the superfamily of peptides without disulfide bridges. This 41-amino acid peptide forms helical structures and has antimicrobial activity against Gram-negative bacteria, such as Salmonella typhi, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Other related peptides, such as Opistoporin-1 (Opistophthalmus carinatus) and Pandinin-1 (Pandinus imperator), both with 44 amino acids, have antimicrobial activity against Gram-positive and Gram-negative bacteria, respectively.
(4) AMPs from the scorpion Heterometrus spinifer have been reported within the group of AMPs with an intermediate size peptide chain; one of these peptides is HsAp (29 amino acids), which has broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, as well as antifungal activity; however, HsAp has limited therapeutic use because it is highly hemolytic against human erythrocytes. Other peptides included in this classification are: Heterin-2 and pandinin-2. Heterin-2 is a venom peptide from the scorpion Heterometrus spinifer which contains 24 amino acid residues. Heterin-2 is able to inhibit the growth of Gram-positive bacteria with MICs from 5.6 μM to 30.0 μM. Pandinin-2 is an α-helical polycationic antimicrobial peptide from venom of the scorpion Pandinus imperator. Pandinin-2 contains 24 amino acid residues and demonstrated high antimicrobial activity against a range of Gram-positive bacteria (2.4–5.2 μM), but was less active against Gram-negative bacteria (2.4–38.2 μM).
(5) Short-chain AMPs or IsCT-type peptides are short antimicrobial peptides derived from longer peptide precursors by post-translational processing of a signal peptide and a carboxy-terminal propeptide region that flank the mature peptide. The mature peptide contains commonly less than 20 amino acids, most of them hydrophobic.
(6) Currently, 67 IsCT-type AMPs have been reported. The first IsCT peptide was isolated from the venom of the scorpion Opisthacanthus madagascariensis; it was named in this way because the scorpion was found in Isalo (Is), Madagascar and the peptide displayed cytotoxic activity (CT). IsCT peptide presents antibacterial activity against Gram-negative and Gram-positive strains of bacteria and low hemolytic activity. Other short peptides from Mexican scorpions have also been identified, e.g., VmCT1 and VmCT2 from the scorpion Vaejovis mexicanus. From the cDNA libraries made from the venom glands of this scorpion belonging to the Vaejovidae family, the sequences of these peptides were identified. The chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity as well as low hemolytic activity. The mechanism of action of these AMPs however is unclear.
(7) Recently, as a result of the transcriptomic analysis of the venomous glands of the Urodacus yaschenkoi scorpion, the existence of a large number of peptides with potential antimicrobial activity (mainly NDBP type) was discovered. The antimicrobial activity of several of these peptides (chemically synthesized) has been evaluated e.g., the UyCT3 peptide with an amidated C-terminal showed strong antimicrobial activity, while the non-amidated UyCT3 peptide failed to exhibit any antimicrobial activity, confirming the importance of the amidation of the C-terminus. The development of new technology platforms for peptide synthesis and modification with a low cost makes peptide systems valuable tools for the design of new therapeutic weapons against multidrug-resistant (MDR) strains.
(8) The rise of MDR bacteria represents a major public health problem worldwide; consequently, global research is focused on the development of new therapeutic agents. Scorpion venoms represent an immense source of bioactive peptides, including toxins that affect the sodium channels of mammals or insects and AMPs. However, only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains. Among NDBPs with antimicrobial activity, scorpion venoms contain peptides such as Opistoporin, Pandinin or IsCT types.
(9) Urodacus yaschenkoi is an Australian scorpion that has been characterized and contains an arsenal of biomolecules with diverse functions, including AMPs. Previous studies have reported that three of these peptides (UyCT1, UyCT3, and UyCT5) have been effective in inhibiting a broad spectrum of bacteria, including MDR pathogens such as Acinetobacter baumannii, and these peptides required the amidation of the C-terminal residue to be active.
(10) Burkholderia cepacia, which is an unusual opportunistic pathogen that threatens immunocompromised patients, was resistant to all the peptides when they were tested individually, even at the highest concentrations that were evaluated. However, the combination of QnCs-BUAP with the peptides Uy234 and Uy192 displayed promising activity against Burkholderia cepacia, with MBCs of 150 μM and 300 μM, respectively. The effectiveness of peptide combinations has been reported, and different advantages of their use have been proposed, such as using lower doses, cost savings, and preventing the development of resistance. Combining the peptide QnCs-BUAP with the peptides Uy234, Uy17, and Uy192 resulted in the reduction of the MBC in almost all bacterial strains evaluated. Furthermore, a synergistic behavior was displayed in 25% of the resulting combinations, 37.5% displayed an additive effect, and only 8% showed antagonism.
(11) Some AMPs from scorpion venom have shown great potential to inhibit the growth of a broad spectrum of bacteria, including MDR clinical isolates; however, their high cytotoxicity and hemolytic activity have prevented their clinical use. According to our results, the three AMPs from U. yaschenkoi and the consensus peptide QnCs-BUAP displayed remarkably low hemolytic activity compared to that of other AMPs from scorpion venom. The hemolytic concentration (HC) of the peptides Uy17, Uy192 and Uy234 towards pig erythrocytes was previously reported with an HC25 = 26.65 μM, 35.85 μM and 55.14 μM, respectively; in our work, the same peptide sequences showed lower hemolytic activity against human erythrocytes, requiring greater peptide concentrations (> 370 μM) to achieve the same HC25.
(12) The mechanism of the antimicrobial action of these AMPs is not fully understood; however, it is generally accepted that the ability of AMPs to kill microorganisms depends upon their capacity to bind to the membranes of these microorganisms. The ability of an AMP to interact with a target membrane depends upon its structure and the membrane target; in the case of short-chain AMPs without cysteine, the α-helical structure of the AMPs is key to achieving the interaction with the membrane target, as is the higher positive charge that is provided by the amidation of the C-terminal residue. The antimicrobial peptides evaluated in this article showed strong activity against Streptococcus sp., while exerted none effect against Burkholderia cepacia, it may be due to Streptococcus sp. is a Gram-positive bacterium, so it does not have an outer cellular membrane making it a sensitive target of the action of the AMPs. On the other hand, Burkholderia cepacia is a Gram-negative bacterium, so it has a double cell membrane representing a double barrier against the action of AMPs.
(13) Furthermore, there is a relationship of bacterial membrane lipid composition and the potency of certain antimicrobial agents. Bacteria vary widely in the lipid composition (cardiolipin, phosphatidylglycerol and phosphatidylethanolamine) of their membranes and would, therefore, be expected to exhibit different sensitivities to antimicrobial compounds. This may explain why the different Gram-Positive and Gram-negative bacteria evaluated in this work have a different degree of susceptibility to the peptides tested. In general, Gram-negative bacteria show higher phosphatidylethanolamine content than Gram-positive bacteria. However, Gram-positive bacteria exhibit a higher amount of anionic lipids (phosphatidylglycerol and cardiolipin). The presence of charge in the lipids favors the electrostatic interactions with cationic AMPs, followed by insertion of peptides in the lipid bilayer and then the AMPs destabilize the membrane making it permeable or disrupting it.
(14) Finally, the synergic effect of each peptide with the QnCs-BUAP peptide may be due to the fact that each combination results in a higher positive charge, which can achieve greater interaction with the lipids of the membrane and lead to destabilize it causing its rupture. The IsCT and IsCT2 peptides from the venom of the African scorpion Opisthacanthus madagascarienis were the first peptides studied of this type of AMP. Structure-function analysis of IsCT and IsCT2 revealed a linear α-helical structure. The reduced antimicrobial activity of non-amidated AMPs is due to the decrease in the positive surface charge and the structural alteration of the α-helix, which affects the ability of the AMP to disrupt the cell membrane. Synergism assays revealed the effectiveness of the combined use of the four peptides, although the mechanism of synergism remains to be elucidated. The antimicrobial peptides evaluated in this work could be valuable tools for the design and development of effective AMPs against bacteria resistant to the currently available antibiotics.1. How many species of scorpions have been discovered so far according to the text?
Correct
(E) is the right answer, notice that in the first paragraph of the text it is stated that 1500 species of scorpions have been studied so far; but the text does not provide the number of species of scorpions discovered so far.
Incorrect
(E) is the right answer, notice that in the first paragraph of the text it is stated that 1500 species of scorpions have been studied so far; but the text does not provide the number of species of scorpions discovered so far.
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Question 2 of 17
2. Question
Structural characterization of scorpion peptides and their bactericidal activity against clinical isolates of multidrug-resistant bacteria
(1) Scorpions are arthropods belonging to the group of arachnids, which have lived on our planet for more than 400 million years. Currently, approximately 1500 species of scorpions have been described, and the study of their venoms has resulted in the discovery of a large arsenal of bioactive molecules; among these molecules, toxins are distinguished by their ability to modulate the function of diverse ion channels and membrane receptors, causing the symptoms of poisoning. Other interesting biomolecules that have been discovered in scorpion venoms are antimicrobial peptides (AMPs), which stand out for their broad-spectrum activity against Gram-positive and Gram-negative bacteria, fungi, yeast, and protozoa. The most interesting AMPs from scorpion venoms are those falling out of the Buthidae family, which do not present any risk to human health; the venoms contain antimicrobial peptides (AMPs) involved in the innate immune response of venomous arthropods. Scorpion AMPs also function as internal immune agents protecting the venom gland from infection and external immune agents cleaning saprophytic microbes from the surface of the scorpion body. In addition, synergistic effects of antimicrobial scorpion peptide and neurotoxins against bacteria has been described, which provides further evidence in favor of the multifunctionality of scorpion venom components. Most of these antimicrobial peptides do not contain disulfide bridges in their structure, known as non-disulfide-bridged peptides (NDBP), and have been classified into several groups, such as scorpine-like, long, intermediate and short-chain AMPs.
(2) Scorpine-like AMPs possess two structural and functional domains: a N-terminal α-helix (with cytolytic and/or antimicrobial activity like the insect defensins) and a tightly folded C-terminal region with a CSαβ motif, displaying K+ channel-blocking activity. The first characterized scorpine was isolated from the venom of the scorpion Pandinus imperator. This protein is formed by 75 amino acids and has shown antimicrobial activity, mainly against Bacillus subtilis, although it also has an inhibitory effect on the ookinete and gamete stages of Plasmodium berghei.
(3) Long-chain AMPs, such as hadrurin (isolated from Mexican scorpion Hadrurus aztecus), belong to the superfamily of peptides without disulfide bridges. This 41-amino acid peptide forms helical structures and has antimicrobial activity against Gram-negative bacteria, such as Salmonella typhi, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Other related peptides, such as Opistoporin-1 (Opistophthalmus carinatus) and Pandinin-1 (Pandinus imperator), both with 44 amino acids, have antimicrobial activity against Gram-positive and Gram-negative bacteria, respectively.
(4) AMPs from the scorpion Heterometrus spinifer have been reported within the group of AMPs with an intermediate size peptide chain; one of these peptides is HsAp (29 amino acids), which has broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, as well as antifungal activity; however, HsAp has limited therapeutic use because it is highly hemolytic against human erythrocytes. Other peptides included in this classification are: Heterin-2 and pandinin-2. Heterin-2 is a venom peptide from the scorpion Heterometrus spinifer which contains 24 amino acid residues. Heterin-2 is able to inhibit the growth of Gram-positive bacteria with MICs from 5.6 μM to 30.0 μM. Pandinin-2 is an α-helical polycationic antimicrobial peptide from venom of the scorpion Pandinus imperator. Pandinin-2 contains 24 amino acid residues and demonstrated high antimicrobial activity against a range of Gram-positive bacteria (2.4–5.2 μM), but was less active against Gram-negative bacteria (2.4–38.2 μM).
(5) Short-chain AMPs or IsCT-type peptides are short antimicrobial peptides derived from longer peptide precursors by post-translational processing of a signal peptide and a carboxy-terminal propeptide region that flank the mature peptide. The mature peptide contains commonly less than 20 amino acids, most of them hydrophobic.
(6) Currently, 67 IsCT-type AMPs have been reported. The first IsCT peptide was isolated from the venom of the scorpion Opisthacanthus madagascariensis; it was named in this way because the scorpion was found in Isalo (Is), Madagascar and the peptide displayed cytotoxic activity (CT). IsCT peptide presents antibacterial activity against Gram-negative and Gram-positive strains of bacteria and low hemolytic activity. Other short peptides from Mexican scorpions have also been identified, e.g., VmCT1 and VmCT2 from the scorpion Vaejovis mexicanus. From the cDNA libraries made from the venom glands of this scorpion belonging to the Vaejovidae family, the sequences of these peptides were identified. The chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity as well as low hemolytic activity. The mechanism of action of these AMPs however is unclear.
(7) Recently, as a result of the transcriptomic analysis of the venomous glands of the Urodacus yaschenkoi scorpion, the existence of a large number of peptides with potential antimicrobial activity (mainly NDBP type) was discovered. The antimicrobial activity of several of these peptides (chemically synthesized) has been evaluated e.g., the UyCT3 peptide with an amidated C-terminal showed strong antimicrobial activity, while the non-amidated UyCT3 peptide failed to exhibit any antimicrobial activity, confirming the importance of the amidation of the C-terminus. The development of new technology platforms for peptide synthesis and modification with a low cost makes peptide systems valuable tools for the design of new therapeutic weapons against multidrug-resistant (MDR) strains.
(8) The rise of MDR bacteria represents a major public health problem worldwide; consequently, global research is focused on the development of new therapeutic agents. Scorpion venoms represent an immense source of bioactive peptides, including toxins that affect the sodium channels of mammals or insects and AMPs. However, only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains. Among NDBPs with antimicrobial activity, scorpion venoms contain peptides such as Opistoporin, Pandinin or IsCT types.
(9) Urodacus yaschenkoi is an Australian scorpion that has been characterized and contains an arsenal of biomolecules with diverse functions, including AMPs. Previous studies have reported that three of these peptides (UyCT1, UyCT3 and UyCT5) have been effective in inhibiting a broad spectrum of bacteria, including MDR pathogens such as Acinetobacter baumannii, and these peptides required the amidation of the C-terminal residue to be active.
(10) Burkholderia cepacia, which is an unusual opportunistic pathogen that threatens immunocompromised patients, was resistant to all the peptides when they were tested individually, even at the highest concentrations that were evaluated. However, the combination of QnCs-BUAP with the peptides Uy234 and Uy192 displayed promising activity against Burkholderia cepacia, with MBCs of 150 μM and 300 μM, respectively. The effectiveness of peptide combinations has been reported, and different advantages of their use have been proposed, such as using lower doses, cost savings, and preventing the development of resistance. Combining the peptide QnCs-BUAP with the peptides Uy234, Uy17, and Uy192 resulted in the reduction of the MBC in almost all bacterial strains evaluated. Furthermore, a synergistic behavior was displayed in 25% of the resulting combinations, 37.5% displayed an additive effect, and only 8% showed antagonism.
(11) Some AMPs from scorpion venom have shown great potential to inhibit the growth of a broad spectrum of bacteria, including MDR clinical isolates; however, their high cytotoxicity and hemolytic activity have prevented their clinical use. According to our results, the three AMPs from U. yaschenkoi and the consensus peptide QnCs-BUAP displayed remarkably low hemolytic activity compared to that of other AMPs from scorpion venom. The hemolytic concentration (HC) of the peptides Uy17, Uy192 and Uy234 towards pig erythrocytes was previously reported with an HC25 = 26.65 μM, 35.85 μM and 55.14 μM, respectively; in our work, the same peptide sequences showed lower hemolytic activity against human erythrocytes, requiring greater peptide concentrations (> 370 μM) to achieve the same HC25.
(12) The mechanism of the antimicrobial action of these AMPs is not fully understood; however, it is generally accepted that the ability of AMPs to kill microorganisms depends upon their capacity to bind to the membranes of these microorganisms. The ability of an AMP to interact with a target membrane depends upon its structure and the membrane target; in the case of short-chain AMPs without cysteine, the α-helical structure of the AMPs is key to achieving the interaction with the membrane target, as is the higher positive charge that is provided by the amidation of the C-terminal residue. The antimicrobial peptides evaluated in this article showed strong activity against Streptococcus sp., while exerted none effect against Burkholderia cepacia, it may be due to Streptococcus sp. is a Gram-positive bacterium, so it does not have an outer cellular membrane making it a sensitive target of the action of the AMPs. On the other hand, Burkholderia cepacia is a Gram-negative bacterium, so it has a double cell membrane representing a double barrier against the action of AMPs.
(13) Furthermore, there is a relationship of bacterial membrane lipid composition and the potency of certain antimicrobial agents. Bacteria vary widely in the lipid composition (cardiolipin, phosphatidylglycerol and phosphatidylethanolamine) of their membranes and would therefore be expected to exhibit different sensitivities to antimicrobial compounds. This may explain why the different Gram-Positive and Gram-negative bacteria evaluated in this work have a different degree of susceptibility to the peptides tested. In general, Gram-negative bacteria show higher phosphatidylethanolamine content than Gram-positive bacteria. However, Gram-positive bacteria exhibit a higher amount of anionic lipids (phosphatidylglycerol and cardiolipin). The presence of charge in the lipids favors the electrostatic interactions with cationic AMPs, followed by insertion of peptides in the lipid bilayer and then the AMPs destabilize the membrane making it permeable or disrupting it.
(14) Finally, the synergic effect of each peptide with the QnCs-BUAP peptide may be due to the fact that each combination results in a higher positive charge, which can achieve greater interaction with the lipids of the membrane and lead to destabilize it causing its rupture. The IsCT and IsCT2 peptides from the venom of the African scorpion Opisthacanthus madagascarienis were the first peptides studied of this type of AMP. Structure-function analysis of IsCT and IsCT2 revealed a linear α-helical structure. The reduced antimicrobial activity of non-amidated AMPs is due to the decrease in the positive surface charge and the structural alteration of the α-helix, which affects the ability of the AMP to disrupt the cell membrane. Synergism assays revealed the effectiveness of the combined use of the four peptides, although the mechanism of synergism remains to be elucidated. The antimicrobial peptides evaluated in this work could be valuable tools for the design and development of effective AMPs against bacteria resistant to the currently available antibiotics.2. Which item is not true about AMPs?
Correct
Answer (A) is the right choice, according to paragraph one we can see all the statements are true except option A. In the last parts of paragraph one we read that “Most of these antimicrobial peptides do not contain disulfide bridges in their structure, known as non-disulfide-bridged peptides (NDBP)…”
Incorrect
Answer (A) is the right choice, according to paragraph one we can see all the statements are true except option A. In the last parts of paragraph one we read that “Most of these antimicrobial peptides do not contain disulfide bridges in their structure, known as non-disulfide-bridged peptides (NDBP)…”
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Question 3 of 17
3. Question
Structural characterization of scorpion peptides and their bactericidal activity against clinical isolates of multidrug-resistant bacteria
(1) Scorpions are arthropods belonging to the group of arachnids, which have lived on our planet for more than 400 million years. Currently, approximately 1500 species of scorpions have been described, and the study of their venoms has resulted in the discovery of a large arsenal of bioactive molecules; among these molecules, toxins are distinguished by their ability to modulate the function of diverse ion channels and membrane receptors, causing the symptoms of poisoning. Other interesting biomolecules that have been discovered in scorpion venoms are antimicrobial peptides (AMPs), which stand out for their broad-spectrum activity against Gram-positive and Gram-negative bacteria, fungi, yeast, and protozoa. The most interesting AMPs from scorpion venoms are those falling out of the Buthidae family, which do not present any risk to human health; the venoms contain antimicrobial peptides (AMPs) involved in the innate immune response of venomous arthropods. Scorpion AMPs also function as internal immune agents protecting the venom gland from infection and external immune agents cleaning saprophytic microbes from the surface of the scorpion body. In addition, synergistic effects of antimicrobial scorpion peptide and neurotoxins against bacteria has been described, which provides further evidence in favor of the multifunctionality of scorpion venom components. Most of these antimicrobial peptides do not contain disulfide bridges in their structure, known as non-disulfide-bridged peptides (NDBP), and have been classified into several groups, such as scorpine-like, long, intermediate and short-chain AMPs.
(2) Scorpine-like AMPs possess two structural and functional domains: a N-terminal α-helix (with cytolytic and/or antimicrobial activity like the insect defensins) and a tightly folded C-terminal region with a CSαβ motif, displaying K+ channel-blocking activity. The first characterized scorpine was isolated from the venom of the scorpion Pandinus imperator. This protein is formed by 75 amino acids and has shown antimicrobial activity, mainly against Bacillus subtilis, although it also has an inhibitory effect on the ookinete and gamete stages of Plasmodium berghei.
(3) Long-chain AMPs, such as hadrurin (isolated from Mexican scorpion Hadrurus aztecus), belong to the superfamily of peptides without disulfide bridges. This 41-amino acid peptide forms helical structures and has antimicrobial activity against Gram-negative bacteria, such as Salmonella typhi, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Other related peptides, such as Opistoporin-1 (Opistophthalmus carinatus) and Pandinin-1 (Pandinus imperator), both with 44 amino acids, have antimicrobial activity against Gram-positive and Gram-negative bacteria, respectively.
(4) AMPs from the scorpion Heterometrus spinifer have been reported within the group of AMPs with an intermediate size peptide chain; one of these peptides is HsAp (29 amino acids), which has broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, as well as antifungal activity; however, HsAp has limited therapeutic use because it is highly hemolytic against human erythrocytes. Other peptides included in this classification are: Heterin-2 and pandinin-2. Heterin-2 is a venom peptide from the scorpion Heterometrus spinifer which contains 24 amino acid residues. Heterin-2 is able to inhibit the growth of Gram-positive bacteria with MICs from 5.6 μM to 30.0 μM. Pandinin-2 is an α-helical polycationic antimicrobial peptide from venom of the scorpion Pandinus imperator. Pandinin-2 contains 24 amino acid residues and demonstrated high antimicrobial activity against a range of Gram-positive bacteria (2.4–5.2 μM), but was less active against Gram-negative bacteria (2.4–38.2 μM).
(5) Short-chain AMPs or IsCT-type peptides are short antimicrobial peptides derived from longer peptide precursors by post-translational processing of a signal peptide and a carboxy-terminal propeptide region that flank the mature peptide. The mature peptide contains commonly less than 20 amino acids, most of them hydrophobic.
(6) Currently, 67 IsCT-type AMPs have been reported. The first IsCT peptide was isolated from the venom of the scorpion Opisthacanthus madagascariensis; it was named in this way because the scorpion was found in Isalo (Is), Madagascar and the peptide displayed cytotoxic activity (CT). IsCT peptide presents antibacterial activity against Gram-negative and Gram-positive strains of bacteria and low hemolytic activity. Other short peptides from Mexican scorpions have also been identified, e.g., VmCT1 and VmCT2 from the scorpion Vaejovis mexicanus. From the cDNA libraries made from the venom glands of this scorpion belonging to the Vaejovidae family, the sequences of these peptides were identified. The chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity as well as low hemolytic activity. The mechanism of action of these AMPs however is unclear.
(7) Recently, as a result of the transcriptomic analysis of the venomous glands of the Urodacus yaschenkoi scorpion, the existence of a large number of peptides with potential antimicrobial activity (mainly NDBP type) was discovered. The antimicrobial activity of several of these peptides (chemically synthesized) has been evaluated e.g., the UyCT3 peptide with an amidated C-terminal showed strong antimicrobial activity, while the non-amidated UyCT3 peptide failed to exhibit any antimicrobial activity, confirming the importance of the amidation of the C-terminus. The development of new technology platforms for peptide synthesis and modification with a low cost makes peptide systems valuable tools for the design of new therapeutic weapons against multidrug-resistant (MDR) strains.
(8) The rise of MDR bacteria represents a major public health problem worldwide; consequently, global research is focused on the development of new therapeutic agents. Scorpion venoms represent an immense source of bioactive peptides, including toxins that affect the sodium channels of mammals or insects and AMPs. However, only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains. Among NDBPs with antimicrobial activity, scorpion venoms contain peptides such as Opistoporin, Pandinin or IsCT types.
(9) Urodacus yaschenkoi is an Australian scorpion that has been characterized and contains an arsenal of biomolecules with diverse functions, including AMPs. Previous studies have reported that three of these peptides (UyCT1, UyCT3 and UyCT5) have been effective in inhibiting a broad spectrum of bacteria, including MDR pathogens such as Acinetobacter baumannii, and these peptides required the amidation of the C-terminal residue to be active.
(10) Burkholderia cepacia, which is an unusual opportunistic pathogen that threatens immunocompromised patients, was resistant to all the peptides when they were tested individually, even at the highest concentrations that were evaluated. However, the combination of QnCs-BUAP with the peptides Uy234 and Uy192 displayed promising activity against Burkholderia cepacia, with MBCs of 150 μM and 300 μM, respectively. The effectiveness of peptide combinations has been reported, and different advantages of their use have been proposed, such as using lower doses, cost savings, and preventing the development of resistance. Combining the peptide QnCs-BUAP with the peptides Uy234, Uy17, and Uy192 resulted in the reduction of the MBC in almost all bacterial strains evaluated. Furthermore, a synergistic behavior was displayed in 25% of the resulting combinations, 37.5% displayed an additive effect, and only 8% showed antagonism.
(11) Some AMPs from scorpion venom have shown great potential to inhibit the growth of a broad spectrum of bacteria, including MDR clinical isolates; however, their high cytotoxicity and hemolytic activity have prevented their clinical use. According to our results, the three AMPs from U. yaschenkoi and the consensus peptide QnCs-BUAP displayed remarkably low hemolytic activity compared to that of other AMPs from scorpion venom. The hemolytic concentration (HC) of the peptides Uy17, Uy192 and Uy234 towards pig erythrocytes was previously reported with an HC25 = 26.65 μM, 35.85 μM and 55.14 μM, respectively; in our work, the same peptide sequences showed lower hemolytic activity against human erythrocytes, requiring greater peptide concentrations (> 370 μM) to achieve the same HC25.
(12) The mechanism of the antimicrobial action of these AMPs is not fully understood; however, it is generally accepted that the ability of AMPs to kill microorganisms depends upon their capacity to bind to the membranes of these microorganisms. The ability of an AMP to interact with a target membrane depends upon its structure and the membrane target; in the case of short-chain AMPs without cysteine, the α-helical structure of the AMPs is key to achieving the interaction with the membrane target, as is the higher positive charge that is provided by the amidation of the C-terminal residue. The antimicrobial peptides evaluated in this article showed strong activity against Streptococcus sp., while exerted none effect against Burkholderia cepacia, it may be due to Streptococcus sp. is a Gram-positive bacterium, so it does not have an outer cellular membrane making it a sensitive target of the action of the AMPs. On the other hand, Burkholderia cepacia is a Gram-negative bacterium, so it has a double cell membrane representing a double barrier against the action of AMPs.
(13) Furthermore, there is a relationship of bacterial membrane lipid composition and the potency of certain antimicrobial agents. Bacteria vary widely in the lipid composition (cardiolipin, phosphatidylglycerol and phosphatidylethanolamine) of their membranes and would therefore be expected to exhibit different sensitivities to antimicrobial compounds. This may explain why the different Gram-Positive and Gram-negative bacteria evaluated in this work have a different degree of susceptibility to the peptides tested. In general, Gram-negative bacteria show higher phosphatidylethanolamine content than Gram-positive bacteria. However, Gram-positive bacteria exhibit a higher amount of anionic lipids (phosphatidylglycerol and cardiolipin). The presence of charge in the lipids favors the electrostatic interactions with cationic AMPs, followed by insertion of peptides in the lipid bilayer and then the AMPs destabilize the membrane making it permeable or disrupting it.
(14) Finally, the synergic effect of each peptide with the QnCs-BUAP peptide may be due to the fact that each combination results in a higher positive charge, which can achieve greater interaction with the lipids of the membrane and lead to destabilize it causing its rupture. The IsCT and IsCT2 peptides from the venom of the African scorpion Opisthacanthus madagascarienis were the first peptides studied of this type of AMP. Structure-function analysis of IsCT and IsCT2 revealed a linear α-helical structure. The reduced antimicrobial activity of non-amidated AMPs is due to the decrease in the positive surface charge and the structural alteration of the α-helix, which affects the ability of the AMP to disrupt the cell membrane. Synergism assays revealed the effectiveness of the combined use of the four peptides, although the mechanism of synergism remains to be elucidated. The antimicrobial peptides evaluated in this work could be valuable tools for the design and development of effective AMPs against bacteria resistant to the currently available antibiotics.3. Which item is not a Gram-negative bacteria?
Correct
Answer (B) is the right choice, according to paragraph three we can see that Opistophthalmus carinatus is a peptide and options A, C and D are Gram-negative bacteria.
Incorrect
Answer (B) is the right choice, according to paragraph three we can see that Opistophthalmus carinatus is a peptide and options A, C and D are Gram-negative bacteria.
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Question 4 of 17
4. Question
Structural characterization of scorpion peptides and their bactericidal activity against clinical isolates of multidrug-resistant bacteria
(1) Scorpions are arthropods belonging to the group of arachnids, which have lived on our planet for more than 400 million years. Currently, approximately 1500 species of scorpions have been described, and the study of their venoms has resulted in the discovery of a large arsenal of bioactive molecules; among these molecules, toxins are distinguished by their ability to modulate the function of diverse ion channels and membrane receptors, causing the symptoms of poisoning. Other interesting biomolecules that have been discovered in scorpion venoms are antimicrobial peptides (AMPs), which stand out for their broad-spectrum activity against Gram-positive and Gram-negative bacteria, fungi, yeast, and protozoa. The most interesting AMPs from scorpion venoms are those falling out of the Buthidae family, which do not present any risk to human health; the venoms contain antimicrobial peptides (AMPs) involved in the innate immune response of venomous arthropods. Scorpion AMPs also function as internal immune agents protecting the venom gland from infection and external immune agents cleaning saprophytic microbes from the surface of the scorpion body. In addition, synergistic effects of antimicrobial scorpion peptide and neurotoxins against bacteria has been described, which provides further evidence in favor of the multifunctionality of scorpion venom components. Most of these antimicrobial peptides do not contain disulfide bridges in their structure, known as non-disulfide-bridged peptides (NDBP), and have been classified into several groups, such as scorpine-like, long, intermediate and short-chain AMPs.
(2) Scorpine-like AMPs possess two structural and functional domains: a N-terminal α-helix (with cytolytic and/or antimicrobial activity like the insect defensins) and a tightly folded C-terminal region with a CSαβ motif, displaying K+ channel-blocking activity. The first characterized scorpine was isolated from the venom of the scorpion Pandinus imperator. This protein is formed by 75 amino acids and has shown antimicrobial activity, mainly against Bacillus subtilis, although it also has an inhibitory effect on the ookinete and gamete stages of Plasmodium berghei.
(3) Long-chain AMPs, such as hadrurin (isolated from Mexican scorpion Hadrurus aztecus), belong to the superfamily of peptides without disulfide bridges. This 41-amino acid peptide forms helical structures and has antimicrobial activity against Gram-negative bacteria, such as Salmonella typhi, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Other related peptides, such as Opistoporin-1 (Opistophthalmus carinatus) and Pandinin-1 (Pandinus imperator), both with 44 amino acids, have antimicrobial activity against Gram-positive and Gram-negative bacteria, respectively.
(4) AMPs from the scorpion Heterometrus spinifer have been reported within the group of AMPs with an intermediate size peptide chain; one of these peptides is HsAp (29 amino acids), which has broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, as well as antifungal activity; however, HsAp has limited therapeutic use because it is highly hemolytic against human erythrocytes. Other peptides included in this classification are: Heterin-2 and pandinin-2. Heterin-2 is a venom peptide from the scorpion Heterometrus spinifer which contains 24 amino acid residues. Heterin-2 is able to inhibit the growth of Gram-positive bacteria with MICs from 5.6 μM to 30.0 μM. Pandinin-2 is an α-helical polycationic antimicrobial peptide from venom of the scorpion Pandinus imperator. Pandinin-2 contains 24 amino acid residues and demonstrated high antimicrobial activity against a range of Gram-positive bacteria (2.4–5.2 μM), but was less active against Gram-negative bacteria (2.4–38.2 μM).
(5) Short-chain AMPs or IsCT-type peptides are short antimicrobial peptides derived from longer peptide precursors by post-translational processing of a signal peptide and a carboxy-terminal propeptide region that flank the mature peptide. The mature peptide contains commonly less than 20 amino acids, most of them hydrophobic.
(6) Currently, 67 IsCT-type AMPs have been reported. The first IsCT peptide was isolated from the venom of the scorpion Opisthacanthus madagascariensis; it was named in this way because the scorpion was found in Isalo (Is), Madagascar and the peptide displayed cytotoxic activity (CT). IsCT peptide presents antibacterial activity against Gram-negative and Gram-positive strains of bacteria and low hemolytic activity. Other short peptides from Mexican scorpions have also been identified, e.g., VmCT1 and VmCT2 from the scorpion Vaejovis mexicanus. From the cDNA libraries made from the venom glands of this scorpion belonging to the Vaejovidae family, the sequences of these peptides were identified. The chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity as well as low hemolytic activity. The mechanism of action of these AMPs however is unclear.
(7) Recently, as a result of the transcriptomic analysis of the venomous glands of the Urodacus yaschenkoi scorpion, the existence of a large number of peptides with potential antimicrobial activity (mainly NDBP type) was discovered. The antimicrobial activity of several of these peptides (chemically synthesized) has been evaluated e.g., the UyCT3 peptide with an amidated C-terminal showed strong antimicrobial activity, while the non-amidated UyCT3 peptide failed to exhibit any antimicrobial activity, confirming the importance of the amidation of the C-terminus. The development of new technology platforms for peptide synthesis and modification with a low cost makes peptide systems valuable tools for the design of new therapeutic weapons against multidrug-resistant (MDR) strains.
(8) The rise of MDR bacteria represents a major public health problem worldwide; consequently, global research is focused on the development of new therapeutic agents. Scorpion venoms represent an immense source of bioactive peptides, including toxins that affect the sodium channels of mammals or insects and AMPs. However, only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains. Among NDBPs with antimicrobial activity, scorpion venoms contain peptides such as Opistoporin, Pandinin or IsCT types.
(9) Urodacus yaschenkoi is an Australian scorpion that has been characterized and contains an arsenal of biomolecules with diverse functions, including AMPs. Previous studies have reported that three of these peptides (UyCT1, UyCT3 and UyCT5) have been effective in inhibiting a broad spectrum of bacteria, including MDR pathogens such as Acinetobacter baumannii, and these peptides required the amidation of the C-terminal residue to be active.
(10) Burkholderia cepacia, which is an unusual opportunistic pathogen that threatens immunocompromised patients, was resistant to all the peptides when they were tested individually, even at the highest concentrations that were evaluated. However, the combination of QnCs-BUAP with the peptides Uy234 and Uy192 displayed promising activity against Burkholderia cepacia, with MBCs of 150 μM and 300 μM, respectively. The effectiveness of peptide combinations has been reported, and different advantages of their use have been proposed, such as using lower doses, cost savings, and preventing the development of resistance. Combining the peptide QnCs-BUAP with the peptides Uy234, Uy17, and Uy192 resulted in the reduction of the MBC in almost all bacterial strains evaluated. Furthermore, a synergistic behavior was displayed in 25% of the resulting combinations, 37.5% displayed an additive effect, and only 8% showed antagonism.
(11) Some AMPs from scorpion venom have shown great potential to inhibit the growth of a broad spectrum of bacteria, including MDR clinical isolates; however, their high cytotoxicity and hemolytic activity have prevented their clinical use. According to our results, the three AMPs from U. yaschenkoi and the consensus peptide QnCs-BUAP displayed remarkably low hemolytic activity compared to that of other AMPs from scorpion venom. The hemolytic concentration (HC) of the peptides Uy17, Uy192 and Uy234 towards pig erythrocytes was previously reported with an HC25 = 26.65 μM, 35.85 μM and 55.14 μM, respectively; in our work, the same peptide sequences showed lower hemolytic activity against human erythrocytes, requiring greater peptide concentrations (> 370 μM) to achieve the same HC25.
(12) The mechanism of the antimicrobial action of these AMPs is not fully understood; however, it is generally accepted that the ability of AMPs to kill microorganisms depends upon their capacity to bind to the membranes of these microorganisms. The ability of an AMP to interact with a target membrane depends upon its structure and the membrane target; in the case of short-chain AMPs without cysteine, the α-helical structure of the AMPs is key to achieving the interaction with the membrane target, as is the higher positive charge that is provided by the amidation of the C-terminal residue. The antimicrobial peptides evaluated in this article showed strong activity against Streptococcus sp., while exerted none effect against Burkholderia cepacia, it may be due to Streptococcus sp. is a Gram-positive bacterium, so it does not have an outer cellular membrane making it a sensitive target of the action of the AMPs. On the other hand, Burkholderia cepacia is a Gram-negative bacterium, so it has a double cell membrane representing a double barrier against the action of AMPs.
(13) Furthermore, there is a relationship of bacterial membrane lipid composition and the potency of certain antimicrobial agents. Bacteria vary widely in the lipid composition (cardiolipin, phosphatidylglycerol and phosphatidylethanolamine) of their membranes and would therefore be expected to exhibit different sensitivities to antimicrobial compounds. This may explain why the different Gram-Positive and Gram-negative bacteria evaluated in this work have a different degree of susceptibility to the peptides tested. In general, Gram-negative bacteria show higher phosphatidylethanolamine content than Gram-positive bacteria. However, Gram-positive bacteria exhibit a higher amount of anionic lipids (phosphatidylglycerol and cardiolipin). The presence of charge in the lipids favors the electrostatic interactions with cationic AMPs, followed by insertion of peptides in the lipid bilayer and then the AMPs destabilize the membrane making it permeable or disrupting it.
(14) Finally, the synergic effect of each peptide with the QnCs-BUAP peptide may be due to the fact that each combination results in a higher positive charge, which can achieve greater interaction with the lipids of the membrane and lead to destabilize it causing its rupture. The IsCT and IsCT2 peptides from the venom of the African scorpion Opisthacanthus madagascarienis were the first peptides studied of this type of AMP. Structure-function analysis of IsCT and IsCT2 revealed a linear α-helical structure. The reduced antimicrobial activity of non-amidated AMPs is due to the decrease in the positive surface charge and the structural alteration of the α-helix, which affects the ability of the AMP to disrupt the cell membrane. Synergism assays revealed the effectiveness of the combined use of the four peptides, although the mechanism of synergism remains to be elucidated. The antimicrobial peptides evaluated in this work could be valuable tools for the design and development of effective AMPs against bacteria resistant to the currently available antibiotics.4. Which item is not true regarding Pandinin-2?
Correct
Answer (C) is the right choice, according to paragraph four we can see that “Heterin-2 is able to inhibit the growth of Gram-positive bacteria with MICs from 5.6 μM to 30.0 μM” and not Pandinin-2. The other items are true regarding Pandinin-2 and you can find them at the end of paragraph four.
Incorrect
Answer (C) is the right choice, according to paragraph four we can see that “Heterin-2 is able to inhibit the growth of Gram-positive bacteria with MICs from 5.6 μM to 30.0 μM” and not Pandinin-2. The other items are true regarding Pandinin-2 and you can find them at the end of paragraph four.
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Question 5 of 17
5. Question
Structural characterization of scorpion peptides and their bactericidal activity against clinical isolates of multidrug-resistant bacteria
(1) Scorpions are arthropods belonging to the group of arachnids, which have lived on our planet for more than 400 million years. Currently, approximately 1500 species of scorpions have been described, and the study of their venoms has resulted in the discovery of a large arsenal of bioactive molecules; among these molecules, toxins are distinguished by their ability to modulate the function of diverse ion channels and membrane receptors, causing the symptoms of poisoning. Other interesting biomolecules that have been discovered in scorpion venoms are antimicrobial peptides (AMPs), which stand out for their broad-spectrum activity against Gram-positive and Gram-negative bacteria, fungi, yeast, and protozoa. The most interesting AMPs from scorpion venoms are those falling out of the Buthidae family, which do not present any risk to human health; the venoms contain antimicrobial peptides (AMPs) involved in the innate immune response of venomous arthropods. Scorpion AMPs also function as internal immune agents protecting the venom gland from infection and external immune agents cleaning saprophytic microbes from the surface of the scorpion body. In addition, synergistic effects of antimicrobial scorpion peptide and neurotoxins against bacteria has been described, which provides further evidence in favor of the multifunctionality of scorpion venom components. Most of these antimicrobial peptides do not contain disulfide bridges in their structure, known as non-disulfide-bridged peptides (NDBP), and have been classified into several groups, such as scorpine-like, long, intermediate and short-chain AMPs.
(2) Scorpine-like AMPs possess two structural and functional domains: a N-terminal α-helix (with cytolytic and/or antimicrobial activity like the insect defensins) and a tightly folded C-terminal region with a CSαβ motif, displaying K+ channel-blocking activity. The first characterized scorpine was isolated from the venom of the scorpion Pandinus imperator. This protein is formed by 75 amino acids and has shown antimicrobial activity, mainly against Bacillus subtilis, although it also has an inhibitory effect on the ookinete and gamete stages of Plasmodium berghei.
(3) Long-chain AMPs, such as hadrurin (isolated from Mexican scorpion Hadrurus aztecus), belong to the superfamily of peptides without disulfide bridges. This 41-amino acid peptide forms helical structures and has antimicrobial activity against Gram-negative bacteria, such as Salmonella typhi, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Other related peptides, such as Opistoporin-1 (Opistophthalmus carinatus) and Pandinin-1 (Pandinus imperator), both with 44 amino acids, have antimicrobial activity against Gram-positive and Gram-negative bacteria, respectively.
(4) AMPs from the scorpion Heterometrus spinifer have been reported within the group of AMPs with an intermediate size peptide chain; one of these peptides is HsAp (29 amino acids), which has broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, as well as antifungal activity; however, HsAp has limited therapeutic use because it is highly hemolytic against human erythrocytes. Other peptides included in this classification are: Heterin-2 and pandinin-2. Heterin-2 is a venom peptide from the scorpion Heterometrus spinifer which contains 24 amino acid residues. Heterin-2 is able to inhibit the growth of Gram-positive bacteria with MICs from 5.6 μM to 30.0 μM. Pandinin-2 is an α-helical polycationic antimicrobial peptide from venom of the scorpion Pandinus imperator. Pandinin-2 contains 24 amino acid residues and demonstrated high antimicrobial activity against a range of Gram-positive bacteria (2.4–5.2 μM), but was less active against Gram-negative bacteria (2.4–38.2 μM).
(5) Short-chain AMPs or IsCT-type peptides are short antimicrobial peptides derived from longer peptide precursors by post-translational processing of a signal peptide and a carboxy-terminal propeptide region that flank the mature peptide. The mature peptide contains commonly less than 20 amino acids, most of them hydrophobic.
(6) Currently, 67 IsCT-type AMPs have been reported. The first IsCT peptide was isolated from the venom of the scorpion Opisthacanthus madagascariensis; it was named in this way because the scorpion was found in Isalo (Is), Madagascar and the peptide displayed cytotoxic activity (CT). IsCT peptide presents antibacterial activity against Gram-negative and Gram-positive strains of bacteria and low hemolytic activity. Other short peptides from Mexican scorpions have also been identified, e.g., VmCT1 and VmCT2 from the scorpion Vaejovis mexicanus. From the cDNA libraries made from the venom glands of this scorpion belonging to the Vaejovidae family, the sequences of these peptides were identified. The chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity as well as low hemolytic activity. The mechanism of action of these AMPs however is unclear.
(7) Recently, as a result of the transcriptomic analysis of the venomous glands of the Urodacus yaschenkoi scorpion, the existence of a large number of peptides with potential antimicrobial activity (mainly NDBP type) was discovered. The antimicrobial activity of several of these peptides (chemically synthesized) has been evaluated e.g., the UyCT3 peptide with an amidated C-terminal showed strong antimicrobial activity, while the non-amidated UyCT3 peptide failed to exhibit any antimicrobial activity, confirming the importance of the amidation of the C-terminus. The development of new technology platforms for peptide synthesis and modification with a low cost makes peptide systems valuable tools for the design of new therapeutic weapons against multidrug-resistant (MDR) strains.
(8) The rise of MDR bacteria represents a major public health problem worldwide; consequently, global research is focused on the development of new therapeutic agents. Scorpion venoms represent an immense source of bioactive peptides, including toxins that affect the sodium channels of mammals or insects and AMPs. However, only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains. Among NDBPs with antimicrobial activity, scorpion venoms contain peptides such as Opistoporin, Pandinin or IsCT types.
(9) Urodacus yaschenkoi is an Australian scorpion that has been characterized and contains an arsenal of biomolecules with diverse functions, including AMPs. Previous studies have reported that three of these peptides (UyCT1, UyCT3 and UyCT5) have been effective in inhibiting a broad spectrum of bacteria, including MDR pathogens such as Acinetobacter baumannii, and these peptides required the amidation of the C-terminal residue to be active.
(10) Burkholderia cepacia, which is an unusual opportunistic pathogen that threatens immunocompromised patients, was resistant to all the peptides when they were tested individually, even at the highest concentrations that were evaluated. However, the combination of QnCs-BUAP with the peptides Uy234 and Uy192 displayed promising activity against Burkholderia cepacia, with MBCs of 150 μM and 300 μM, respectively. The effectiveness of peptide combinations has been reported, and different advantages of their use have been proposed, such as using lower doses, cost savings, and preventing the development of resistance. Combining the peptide QnCs-BUAP with the peptides Uy234, Uy17, and Uy192 resulted in the reduction of the MBC in almost all bacterial strains evaluated. Furthermore, a synergistic behavior was displayed in 25% of the resulting combinations, 37.5% displayed an additive effect, and only 8% showed antagonism.
(11) Some AMPs from scorpion venom have shown great potential to inhibit the growth of a broad spectrum of bacteria, including MDR clinical isolates; however, their high cytotoxicity and hemolytic activity have prevented their clinical use. According to our results, the three AMPs from U. yaschenkoi and the consensus peptide QnCs-BUAP displayed remarkably low hemolytic activity compared to that of other AMPs from scorpion venom. The hemolytic concentration (HC) of the peptides Uy17, Uy192 and Uy234 towards pig erythrocytes was previously reported with an HC25 = 26.65 μM, 35.85 μM and 55.14 μM, respectively; in our work, the same peptide sequences showed lower hemolytic activity against human erythrocytes, requiring greater peptide concentrations (> 370 μM) to achieve the same HC25.
(12) The mechanism of the antimicrobial action of these AMPs is not fully understood; however, it is generally accepted that the ability of AMPs to kill microorganisms depends upon their capacity to bind to the membranes of these microorganisms. The ability of an AMP to interact with a target membrane depends upon its structure and the membrane target; in the case of short-chain AMPs without cysteine, the α-helical structure of the AMPs is key to achieving the interaction with the membrane target, as is the higher positive charge that is provided by the amidation of the C-terminal residue. The antimicrobial peptides evaluated in this article showed strong activity against Streptococcus sp., while exerted none effect against Burkholderia cepacia, it may be due to Streptococcus sp. is a Gram-positive bacterium, so it does not have an outer cellular membrane making it a sensitive target of the action of the AMPs. On the other hand, Burkholderia cepacia is a Gram-negative bacterium, so it has a double cell membrane representing a double barrier against the action of AMPs.
(13) Furthermore, there is a relationship of bacterial membrane lipid composition and the potency of certain antimicrobial agents. Bacteria vary widely in the lipid composition (cardiolipin, phosphatidylglycerol and phosphatidylethanolamine) of their membranes and would therefore be expected to exhibit different sensitivities to antimicrobial compounds. This may explain why the different Gram-Positive and Gram-negative bacteria evaluated in this work have a different degree of susceptibility to the peptides tested. In general, Gram-negative bacteria show higher phosphatidylethanolamine content than Gram-positive bacteria. However, Gram-positive bacteria exhibit a higher amount of anionic lipids (phosphatidylglycerol and cardiolipin). The presence of charge in the lipids favors the electrostatic interactions with cationic AMPs, followed by insertion of peptides in the lipid bilayer and then the AMPs destabilize the membrane making it permeable or disrupting it.
(14) Finally, the synergic effect of each peptide with the QnCs-BUAP peptide may be due to the fact that each combination results in a higher positive charge, which can achieve greater interaction with the lipids of the membrane and lead to destabilize it causing its rupture. The IsCT and IsCT2 peptides from the venom of the African scorpion Opisthacanthus madagascarienis were the first peptides studied of this type of AMP. Structure-function analysis of IsCT and IsCT2 revealed a linear α-helical structure. The reduced antimicrobial activity of non-amidated AMPs is due to the decrease in the positive surface charge and the structural alteration of the α-helix, which affects the ability of the AMP to disrupt the cell membrane. Synergism assays revealed the effectiveness of the combined use of the four peptides, although the mechanism of synergism remains to be elucidated. The antimicrobial peptides evaluated in this work could be valuable tools for the design and development of effective AMPs against bacteria resistant to the currently available antibiotics.5. Scientists discovered that the chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity.
The mechanism of action of these AMPs has been discovered.Correct
Answer (D) is the right choice since at the end of paragraph six it is stated that “The chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity as well as low hemolytic activity.” But it is also said that the mechanism of action of these AMPs is not clear.
Incorrect
Answer (D) is the right choice since at the end of paragraph six it is stated that “The chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity as well as low hemolytic activity.” But it is also said that the mechanism of action of these AMPs is not clear.
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Question 6 of 17
6. Question
Structural characterization of scorpion peptides and their bactericidal activity against clinical isolates of multidrug-resistant bacteria
(1) Scorpions are arthropods belonging to the group of arachnids, which have lived on our planet for more than 400 million years. Currently, approximately 1500 species of scorpions have been described, and the study of their venoms has resulted in the discovery of a large arsenal of bioactive molecules; among these molecules, toxins are distinguished by their ability to modulate the function of diverse ion channels and membrane receptors, causing the symptoms of poisoning. Other interesting biomolecules that have been discovered in scorpion venoms are antimicrobial peptides (AMPs), which stand out for their broad-spectrum activity against Gram-positive and Gram-negative bacteria, fungi, yeast, and protozoa. The most interesting AMPs from scorpion venoms are those falling out of the Buthidae family, which do not present any risk to human health; the venoms contain antimicrobial peptides (AMPs) involved in the innate immune response of venomous arthropods. Scorpion AMPs also function as internal immune agents protecting the venom gland from infection and external immune agents cleaning saprophytic microbes from the surface of the scorpion body. In addition, synergistic effects of antimicrobial scorpion peptide and neurotoxins against bacteria has been described, which provides further evidence in favor of the multifunctionality of scorpion venom components. Most of these antimicrobial peptides do not contain disulfide bridges in their structure, known as non-disulfide-bridged peptides (NDBP), and have been classified into several groups, such as scorpine-like, long, intermediate and short-chain AMPs.
(2) Scorpine-like AMPs possess two structural and functional domains: a N-terminal α-helix (with cytolytic and/or antimicrobial activity like the insect defensins) and a tightly folded C-terminal region with a CSαβ motif, displaying K+ channel-blocking activity. The first characterized scorpine was isolated from the venom of the scorpion Pandinus imperator. This protein is formed by 75 amino acids and has shown antimicrobial activity, mainly against Bacillus subtilis, although it also has an inhibitory effect on the ookinete and gamete stages of Plasmodium berghei.
(3) Long-chain AMPs, such as hadrurin (isolated from Mexican scorpion Hadrurus aztecus), belong to the superfamily of peptides without disulfide bridges. This 41-amino acid peptide forms helical structures and has antimicrobial activity against Gram-negative bacteria, such as Salmonella typhi, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Other related peptides, such as Opistoporin-1 (Opistophthalmus carinatus) and Pandinin-1 (Pandinus imperator), both with 44 amino acids, have antimicrobial activity against Gram-positive and Gram-negative bacteria, respectively.
(4) AMPs from the scorpion Heterometrus spinifer have been reported within the group of AMPs with an intermediate size peptide chain; one of these peptides is HsAp (29 amino acids), which has broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, as well as antifungal activity; however, HsAp has limited therapeutic use because it is highly hemolytic against human erythrocytes. Other peptides included in this classification are: Heterin-2 and pandinin-2. Heterin-2 is a venom peptide from the scorpion Heterometrus spinifer which contains 24 amino acid residues. Heterin-2 is able to inhibit the growth of Gram-positive bacteria with MICs from 5.6 μM to 30.0 μM. Pandinin-2 is an α-helical polycationic antimicrobial peptide from venom of the scorpion Pandinus imperator. Pandinin-2 contains 24 amino acid residues and demonstrated high antimicrobial activity against a range of Gram-positive bacteria (2.4–5.2 μM), but was less active against Gram-negative bacteria (2.4–38.2 μM).
(5) Short-chain AMPs or IsCT-type peptides are short antimicrobial peptides derived from longer peptide precursors by post-translational processing of a signal peptide and a carboxy-terminal propeptide region that flank the mature peptide. The mature peptide contains commonly less than 20 amino acids, most of them hydrophobic.
(6) Currently, 67 IsCT-type AMPs have been reported. The first IsCT peptide was isolated from the venom of the scorpion Opisthacanthus madagascariensis; it was named in this way because the scorpion was found in Isalo (Is), Madagascar and the peptide displayed cytotoxic activity (CT). IsCT peptide presents antibacterial activity against Gram-negative and Gram-positive strains of bacteria and low hemolytic activity. Other short peptides from Mexican scorpions have also been identified, e.g., VmCT1 and VmCT2 from the scorpion Vaejovis mexicanus. From the cDNA libraries made from the venom glands of this scorpion belonging to the Vaejovidae family, the sequences of these peptides were identified. The chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity as well as low hemolytic activity. The mechanism of action of these AMPs however is unclear.
(7) Recently, as a result of the transcriptomic analysis of the venomous glands of the Urodacus yaschenkoi scorpion, the existence of a large number of peptides with potential antimicrobial activity (mainly NDBP type) was discovered. The antimicrobial activity of several of these peptides (chemically synthesized) has been evaluated e.g., the UyCT3 peptide with an amidated C-terminal showed strong antimicrobial activity, while the non-amidated UyCT3 peptide failed to exhibit any antimicrobial activity, confirming the importance of the amidation of the C-terminus. The development of new technology platforms for peptide synthesis and modification with a low cost makes peptide systems valuable tools for the design of new therapeutic weapons against multidrug-resistant (MDR) strains.
(8) The rise of MDR bacteria represents a major public health problem worldwide; consequently, global research is focused on the development of new therapeutic agents. Scorpion venoms represent an immense source of bioactive peptides, including toxins that affect the sodium channels of mammals or insects and AMPs. However, only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains. Among NDBPs with antimicrobial activity, scorpion venoms contain peptides such as Opistoporin, Pandinin or IsCT types.
(9) Urodacus yaschenkoi is an Australian scorpion that has been characterized and contains an arsenal of biomolecules with diverse functions, including AMPs. Previous studies have reported that three of these peptides (UyCT1, UyCT3 and UyCT5) have been effective in inhibiting a broad spectrum of bacteria, including MDR pathogens such as Acinetobacter baumannii, and these peptides required the amidation of the C-terminal residue to be active.
(10) Burkholderia cepacia, which is an unusual opportunistic pathogen that threatens immunocompromised patients, was resistant to all the peptides when they were tested individually, even at the highest concentrations that were evaluated. However, the combination of QnCs-BUAP with the peptides Uy234 and Uy192 displayed promising activity against Burkholderia cepacia, with MBCs of 150 μM and 300 μM, respectively. The effectiveness of peptide combinations has been reported, and different advantages of their use have been proposed, such as using lower doses, cost savings, and preventing the development of resistance. Combining the peptide QnCs-BUAP with the peptides Uy234, Uy17, and Uy192 resulted in the reduction of the MBC in almost all bacterial strains evaluated. Furthermore, a synergistic behavior was displayed in 25% of the resulting combinations, 37.5% displayed an additive effect, and only 8% showed antagonism.
(11) Some AMPs from scorpion venom have shown great potential to inhibit the growth of a broad spectrum of bacteria, including MDR clinical isolates; however, their high cytotoxicity and hemolytic activity have prevented their clinical use. According to our results, the three AMPs from U. yaschenkoi and the consensus peptide QnCs-BUAP displayed remarkably low hemolytic activity compared to that of other AMPs from scorpion venom. The hemolytic concentration (HC) of the peptides Uy17, Uy192 and Uy234 towards pig erythrocytes was previously reported with an HC25 = 26.65 μM, 35.85 μM and 55.14 μM, respectively; in our work, the same peptide sequences showed lower hemolytic activity against human erythrocytes, requiring greater peptide concentrations (> 370 μM) to achieve the same HC25.
(12) The mechanism of the antimicrobial action of these AMPs is not fully understood; however, it is generally accepted that the ability of AMPs to kill microorganisms depends upon their capacity to bind to the membranes of these microorganisms. The ability of an AMP to interact with a target membrane depends upon its structure and the membrane target; in the case of short-chain AMPs without cysteine, the α-helical structure of the AMPs is key to achieving the interaction with the membrane target, as is the higher positive charge that is provided by the amidation of the C-terminal residue. The antimicrobial peptides evaluated in this article showed strong activity against Streptococcus sp., while exerted none effect against Burkholderia cepacia, it may be due to Streptococcus sp. is a Gram-positive bacterium, so it does not have an outer cellular membrane making it a sensitive target of the action of the AMPs. On the other hand, Burkholderia cepacia is a Gram-negative bacterium, so it has a double cell membrane representing a double barrier against the action of AMPs.
(13) Furthermore, there is a relationship of bacterial membrane lipid composition and the potency of certain antimicrobial agents. Bacteria vary widely in the lipid composition (cardiolipin, phosphatidylglycerol and phosphatidylethanolamine) of their membranes and would therefore be expected to exhibit different sensitivities to antimicrobial compounds. This may explain why the different Gram-Positive and Gram-negative bacteria evaluated in this work have a different degree of susceptibility to the peptides tested. In general, Gram-negative bacteria show higher phosphatidylethanolamine content than Gram-positive bacteria. However, Gram-positive bacteria exhibit a higher amount of anionic lipids (phosphatidylglycerol and cardiolipin). The presence of charge in the lipids favors the electrostatic interactions with cationic AMPs, followed by insertion of peptides in the lipid bilayer and then the AMPs destabilize the membrane making it permeable or disrupting it.
(14) Finally, the synergic effect of each peptide with the QnCs-BUAP peptide may be due to the fact that each combination results in a higher positive charge, which can achieve greater interaction with the lipids of the membrane and lead to destabilize it causing its rupture. The IsCT and IsCT2 peptides from the venom of the African scorpion Opisthacanthus madagascarienis were the first peptides studied of this type of AMP. Structure-function analysis of IsCT and IsCT2 revealed a linear α-helical structure. The reduced antimicrobial activity of non-amidated AMPs is due to the decrease in the positive surface charge and the structural alteration of the α-helix, which affects the ability of the AMP to disrupt the cell membrane. Synergism assays revealed the effectiveness of the combined use of the four peptides, although the mechanism of synergism remains to be elucidated. The antimicrobial peptides evaluated in this work could be valuable tools for the design and development of effective AMPs against bacteria resistant to the currently available antibiotics.6. What was the result of the analysis of antimicrobial peptides in venomous glands of Urodacus yaschenkoi scorpion?
Correct
Answer (E) is the right choice, in paragraph seven we can see that the items provided here are all results of the analysis of antimicrobial peptides in venomous glands of Urodacus yaschenkoi scorpion.
Incorrect
Answer (E) is the right choice, in paragraph seven we can see that the items provided here are all results of the analysis of antimicrobial peptides in venomous glands of Urodacus yaschenkoi scorpion.
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Question 7 of 17
7. Question
Structural characterization of scorpion peptides and their bactericidal activity against clinical isolates of multidrug-resistant bacteria
(1) Scorpions are arthropods belonging to the group of arachnids, which have lived on our planet for more than 400 million years. Currently, approximately 1500 species of scorpions have been described, and the study of their venoms has resulted in the discovery of a large arsenal of bioactive molecules; among these molecules, toxins are distinguished by their ability to modulate the function of diverse ion channels and membrane receptors, causing the symptoms of poisoning. Other interesting biomolecules that have been discovered in scorpion venoms are antimicrobial peptides (AMPs), which stand out for their broad-spectrum activity against Gram-positive and Gram-negative bacteria, fungi, yeast, and protozoa. The most interesting AMPs from scorpion venoms are those falling out of the Buthidae family, which do not present any risk to human health; the venoms contain antimicrobial peptides (AMPs) involved in the innate immune response of venomous arthropods. Scorpion AMPs also function as internal immune agents protecting the venom gland from infection and external immune agents cleaning saprophytic microbes from the surface of the scorpion body. In addition, synergistic effects of antimicrobial scorpion peptide and neurotoxins against bacteria has been described, which provides further evidence in favor of the multifunctionality of scorpion venom components. Most of these antimicrobial peptides do not contain disulfide bridges in their structure, known as non-disulfide-bridged peptides (NDBP), and have been classified into several groups, such as scorpine-like, long, intermediate and short-chain AMPs.
(2) Scorpine-like AMPs possess two structural and functional domains: a N-terminal α-helix (with cytolytic and/or antimicrobial activity like the insect defensins) and a tightly folded C-terminal region with a CSαβ motif, displaying K+ channel-blocking activity. The first characterized scorpine was isolated from the venom of the scorpion Pandinus imperator. This protein is formed by 75 amino acids and has shown antimicrobial activity, mainly against Bacillus subtilis, although it also has an inhibitory effect on the ookinete and gamete stages of Plasmodium berghei.
(3) Long-chain AMPs, such as hadrurin (isolated from Mexican scorpion Hadrurus aztecus), belong to the superfamily of peptides without disulfide bridges. This 41-amino acid peptide forms helical structures and has antimicrobial activity against Gram-negative bacteria, such as Salmonella typhi, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Other related peptides, such as Opistoporin-1 (Opistophthalmus carinatus) and Pandinin-1 (Pandinus imperator), both with 44 amino acids, have antimicrobial activity against Gram-positive and Gram-negative bacteria, respectively.
(4) AMPs from the scorpion Heterometrus spinifer have been reported within the group of AMPs with an intermediate size peptide chain; one of these peptides is HsAp (29 amino acids), which has broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, as well as antifungal activity; however, HsAp has limited therapeutic use because it is highly hemolytic against human erythrocytes. Other peptides included in this classification are: Heterin-2 and pandinin-2. Heterin-2 is a venom peptide from the scorpion Heterometrus spinifer which contains 24 amino acid residues. Heterin-2 is able to inhibit the growth of Gram-positive bacteria with MICs from 5.6 μM to 30.0 μM. Pandinin-2 is an α-helical polycationic antimicrobial peptide from venom of the scorpion Pandinus imperator. Pandinin-2 contains 24 amino acid residues and demonstrated high antimicrobial activity against a range of Gram-positive bacteria (2.4–5.2 μM), but was less active against Gram-negative bacteria (2.4–38.2 μM).
(5) Short-chain AMPs or IsCT-type peptides are short antimicrobial peptides derived from longer peptide precursors by post-translational processing of a signal peptide and a carboxy-terminal propeptide region that flank the mature peptide. The mature peptide contains commonly less than 20 amino acids, most of them hydrophobic.
(6) Currently, 67 IsCT-type AMPs have been reported. The first IsCT peptide was isolated from the venom of the scorpion Opisthacanthus madagascariensis; it was named in this way because the scorpion was found in Isalo (Is), Madagascar and the peptide displayed cytotoxic activity (CT). IsCT peptide presents antibacterial activity against Gram-negative and Gram-positive strains of bacteria and low hemolytic activity. Other short peptides from Mexican scorpions have also been identified, e.g., VmCT1 and VmCT2 from the scorpion Vaejovis mexicanus. From the cDNA libraries made from the venom glands of this scorpion belonging to the Vaejovidae family, the sequences of these peptides were identified. The chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity as well as low hemolytic activity. The mechanism of action of these AMPs however is unclear.
(7) Recently, as a result of the transcriptomic analysis of the venomous glands of the Urodacus yaschenkoi scorpion, the existence of a large number of peptides with potential antimicrobial activity (mainly NDBP type) was discovered. The antimicrobial activity of several of these peptides (chemically synthesized) has been evaluated e.g., the UyCT3 peptide with an amidated C-terminal showed strong antimicrobial activity, while the non-amidated UyCT3 peptide failed to exhibit any antimicrobial activity, confirming the importance of the amidation of the C-terminus. The development of new technology platforms for peptide synthesis and modification with a low cost makes peptide systems valuable tools for the design of new therapeutic weapons against multidrug-resistant (MDR) strains.
(8) The rise of MDR bacteria represents a major public health problem worldwide; consequently, global research is focused on the development of new therapeutic agents. Scorpion venoms represent an immense source of bioactive peptides, including toxins that affect the sodium channels of mammals or insects and AMPs. However, only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains. Among NDBPs with antimicrobial activity, scorpion venoms contain peptides such as Opistoporin, Pandinin or IsCT types.
(9) Urodacus yaschenkoi is an Australian scorpion that has been characterized and contains an arsenal of biomolecules with diverse functions, including AMPs. Previous studies have reported that three of these peptides (UyCT1, UyCT3 and UyCT5) have been effective in inhibiting a broad spectrum of bacteria, including MDR pathogens such as Acinetobacter baumannii, and these peptides required the amidation of the C-terminal residue to be active.
(10) Burkholderia cepacia, which is an unusual opportunistic pathogen that threatens immunocompromised patients, was resistant to all the peptides when they were tested individually, even at the highest concentrations that were evaluated. However, the combination of QnCs-BUAP with the peptides Uy234 and Uy192 displayed promising activity against Burkholderia cepacia, with MBCs of 150 μM and 300 μM, respectively. The effectiveness of peptide combinations has been reported, and different advantages of their use have been proposed, such as using lower doses, cost savings, and preventing the development of resistance. Combining the peptide QnCs-BUAP with the peptides Uy234, Uy17, and Uy192 resulted in the reduction of the MBC in almost all bacterial strains evaluated. Furthermore, a synergistic behavior was displayed in 25% of the resulting combinations, 37.5% displayed an additive effect, and only 8% showed antagonism.
(11) Some AMPs from scorpion venom have shown great potential to inhibit the growth of a broad spectrum of bacteria, including MDR clinical isolates; however, their high cytotoxicity and hemolytic activity have prevented their clinical use. According to our results, the three AMPs from U. yaschenkoi and the consensus peptide QnCs-BUAP displayed remarkably low hemolytic activity compared to that of other AMPs from scorpion venom. The hemolytic concentration (HC) of the peptides Uy17, Uy192 and Uy234 towards pig erythrocytes was previously reported with an HC25 = 26.65 μM, 35.85 μM and 55.14 μM, respectively; in our work, the same peptide sequences showed lower hemolytic activity against human erythrocytes, requiring greater peptide concentrations (> 370 μM) to achieve the same HC25.
(12) The mechanism of the antimicrobial action of these AMPs is not fully understood; however, it is generally accepted that the ability of AMPs to kill microorganisms depends upon their capacity to bind to the membranes of these microorganisms. The ability of an AMP to interact with a target membrane depends upon its structure and the membrane target; in the case of short-chain AMPs without cysteine, the α-helical structure of the AMPs is key to achieving the interaction with the membrane target, as is the higher positive charge that is provided by the amidation of the C-terminal residue. The antimicrobial peptides evaluated in this article showed strong activity against Streptococcus sp., while exerted none effect against Burkholderia cepacia, it may be due to Streptococcus sp. is a Gram-positive bacterium, so it does not have an outer cellular membrane making it a sensitive target of the action of the AMPs. On the other hand, Burkholderia cepacia is a Gram-negative bacterium, so it has a double cell membrane representing a double barrier against the action of AMPs.
(13) Furthermore, there is a relationship of bacterial membrane lipid composition and the potency of certain antimicrobial agents. Bacteria vary widely in the lipid composition (cardiolipin, phosphatidylglycerol and phosphatidylethanolamine) of their membranes and would therefore be expected to exhibit different sensitivities to antimicrobial compounds. This may explain why the different Gram-Positive and Gram-negative bacteria evaluated in this work have a different degree of susceptibility to the peptides tested. In general, Gram-negative bacteria show higher phosphatidylethanolamine content than Gram-positive bacteria. However, Gram-positive bacteria exhibit a higher amount of anionic lipids (phosphatidylglycerol and cardiolipin). The presence of charge in the lipids favors the electrostatic interactions with cationic AMPs, followed by insertion of peptides in the lipid bilayer and then the AMPs destabilize the membrane making it permeable or disrupting it.
(14) Finally, the synergic effect of each peptide with the QnCs-BUAP peptide may be due to the fact that each combination results in a higher positive charge, which can achieve greater interaction with the lipids of the membrane and lead to destabilize it causing its rupture. The IsCT and IsCT2 peptides from the venom of the African scorpion Opisthacanthus madagascarienis were the first peptides studied of this type of AMP. Structure-function analysis of IsCT and IsCT2 revealed a linear α-helical structure. The reduced antimicrobial activity of non-amidated AMPs is due to the decrease in the positive surface charge and the structural alteration of the α-helix, which affects the ability of the AMP to disrupt the cell membrane. Synergism assays revealed the effectiveness of the combined use of the four peptides, although the mechanism of synergism remains to be elucidated. The antimicrobial peptides evaluated in this work could be valuable tools for the design and development of effective AMPs against bacteria resistant to the currently available antibiotics.7. Scorpion venoms are a great source of bioactive peptides.
Only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains.Correct
Answer (A) is the right choice, in paragraph eight it is stated that “Scorpion venoms represent an immense source of bioactive peptides, including toxins that affect the sodium channels of mammals or insects and AMPs. However, only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains.”
Incorrect
Answer (A) is the right choice, in paragraph eight it is stated that “Scorpion venoms represent an immense source of bioactive peptides, including toxins that affect the sodium channels of mammals or insects and AMPs. However, only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains.”
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Question 8 of 17
8. Question
Structural characterization of scorpion peptides and their bactericidal activity against clinical isolates of multidrug-resistant bacteria
(1) Scorpions are arthropods belonging to the group of arachnids, which have lived on our planet for more than 400 million years. Currently, approximately 1500 species of scorpions have been described, and the study of their venoms has resulted in the discovery of a large arsenal of bioactive molecules; among these molecules, toxins are distinguished by their ability to modulate the function of diverse ion channels and membrane receptors, causing the symptoms of poisoning. Other interesting biomolecules that have been discovered in scorpion venoms are antimicrobial peptides (AMPs), which stand out for their broad-spectrum activity against Gram-positive and Gram-negative bacteria, fungi, yeast, and protozoa. The most interesting AMPs from scorpion venoms are those falling out of the Buthidae family, which do not present any risk to human health; the venoms contain antimicrobial peptides (AMPs) involved in the innate immune response of venomous arthropods. Scorpion AMPs also function as internal immune agents protecting the venom gland from infection and external immune agents cleaning saprophytic microbes from the surface of the scorpion body. In addition, synergistic effects of antimicrobial scorpion peptide and neurotoxins against bacteria has been described, which provides further evidence in favor of the multifunctionality of scorpion venom components. Most of these antimicrobial peptides do not contain disulfide bridges in their structure, known as non-disulfide-bridged peptides (NDBP), and have been classified into several groups, such as scorpine-like, long, intermediate and short-chain AMPs.
(2) Scorpine-like AMPs possess two structural and functional domains: a N-terminal α-helix (with cytolytic and/or antimicrobial activity like the insect defensins) and a tightly folded C-terminal region with a CSαβ motif, displaying K+ channel-blocking activity. The first characterized scorpine was isolated from the venom of the scorpion Pandinus imperator. This protein is formed by 75 amino acids and has shown antimicrobial activity, mainly against Bacillus subtilis, although it also has an inhibitory effect on the ookinete and gamete stages of Plasmodium berghei.
(3) Long-chain AMPs, such as hadrurin (isolated from Mexican scorpion Hadrurus aztecus), belong to the superfamily of peptides without disulfide bridges. This 41-amino acid peptide forms helical structures and has antimicrobial activity against Gram-negative bacteria, such as Salmonella typhi, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Other related peptides, such as Opistoporin-1 (Opistophthalmus carinatus) and Pandinin-1 (Pandinus imperator), both with 44 amino acids, have antimicrobial activity against Gram-positive and Gram-negative bacteria, respectively.
(4) AMPs from the scorpion Heterometrus spinifer have been reported within the group of AMPs with an intermediate size peptide chain; one of these peptides is HsAp (29 amino acids), which has broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, as well as antifungal activity; however, HsAp has limited therapeutic use because it is highly hemolytic against human erythrocytes. Other peptides included in this classification are: Heterin-2 and pandinin-2. Heterin-2 is a venom peptide from the scorpion Heterometrus spinifer which contains 24 amino acid residues. Heterin-2 is able to inhibit the growth of Gram-positive bacteria with MICs from 5.6 μM to 30.0 μM. Pandinin-2 is an α-helical polycationic antimicrobial peptide from venom of the scorpion Pandinus imperator. Pandinin-2 contains 24 amino acid residues and demonstrated high antimicrobial activity against a range of Gram-positive bacteria (2.4–5.2 μM), but was less active against Gram-negative bacteria (2.4–38.2 μM).
(5) Short-chain AMPs or IsCT-type peptides are short antimicrobial peptides derived from longer peptide precursors by post-translational processing of a signal peptide and a carboxy-terminal propeptide region that flank the mature peptide. The mature peptide contains commonly less than 20 amino acids, most of them hydrophobic.
(6) Currently, 67 IsCT-type AMPs have been reported. The first IsCT peptide was isolated from the venom of the scorpion Opisthacanthus madagascariensis; it was named in this way because the scorpion was found in Isalo (Is), Madagascar and the peptide displayed cytotoxic activity (CT). IsCT peptide presents antibacterial activity against Gram-negative and Gram-positive strains of bacteria and low hemolytic activity. Other short peptides from Mexican scorpions have also been identified, e.g., VmCT1 and VmCT2 from the scorpion Vaejovis mexicanus. From the cDNA libraries made from the venom glands of this scorpion belonging to the Vaejovidae family, the sequences of these peptides were identified. The chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity as well as low hemolytic activity. The mechanism of action of these AMPs however is unclear.
(7) Recently, as a result of the transcriptomic analysis of the venomous glands of the Urodacus yaschenkoi scorpion, the existence of a large number of peptides with potential antimicrobial activity (mainly NDBP type) was discovered. The antimicrobial activity of several of these peptides (chemically synthesized) has been evaluated e.g., the UyCT3 peptide with an amidated C-terminal showed strong antimicrobial activity, while the non-amidated UyCT3 peptide failed to exhibit any antimicrobial activity, confirming the importance of the amidation of the C-terminus. The development of new technology platforms for peptide synthesis and modification with a low cost makes peptide systems valuable tools for the design of new therapeutic weapons against multidrug-resistant (MDR) strains.
(8) The rise of MDR bacteria represents a major public health problem worldwide; consequently, global research is focused on the development of new therapeutic agents. Scorpion venoms represent an immense source of bioactive peptides, including toxins that affect the sodium channels of mammals or insects and AMPs. However, only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains. Among NDBPs with antimicrobial activity, scorpion venoms contain peptides such as Opistoporin, Pandinin or IsCT types.
(9) Urodacus yaschenkoi is an Australian scorpion that has been characterized and contains an arsenal of biomolecules with diverse functions, including AMPs. Previous studies have reported that three of these peptides (UyCT1, UyCT3 and UyCT5) have been effective in inhibiting a broad spectrum of bacteria, including MDR pathogens such as Acinetobacter baumannii, and these peptides required the amidation of the C-terminal residue to be active.
(10) Burkholderia cepacia, which is an unusual opportunistic pathogen that threatens immunocompromised patients, was resistant to all the peptides when they were tested individually, even at the highest concentrations that were evaluated. However, the combination of QnCs-BUAP with the peptides Uy234 and Uy192 displayed promising activity against Burkholderia cepacia, with MBCs of 150 μM and 300 μM, respectively. The effectiveness of peptide combinations has been reported, and different advantages of their use have been proposed, such as using lower doses, cost savings, and preventing the development of resistance. Combining the peptide QnCs-BUAP with the peptides Uy234, Uy17, and Uy192 resulted in the reduction of the MBC in almost all bacterial strains evaluated. Furthermore, a synergistic behavior was displayed in 25% of the resulting combinations, 37.5% displayed an additive effect, and only 8% showed antagonism.
(11) Some AMPs from scorpion venom have shown great potential to inhibit the growth of a broad spectrum of bacteria, including MDR clinical isolates; however, their high cytotoxicity and hemolytic activity have prevented their clinical use. According to our results, the three AMPs from U. yaschenkoi and the consensus peptide QnCs-BUAP displayed remarkably low hemolytic activity compared to that of other AMPs from scorpion venom. The hemolytic concentration (HC) of the peptides Uy17, Uy192 and Uy234 towards pig erythrocytes was previously reported with an HC25 = 26.65 μM, 35.85 μM and 55.14 μM, respectively; in our work, the same peptide sequences showed lower hemolytic activity against human erythrocytes, requiring greater peptide concentrations (> 370 μM) to achieve the same HC25.
(12) The mechanism of the antimicrobial action of these AMPs is not fully understood; however, it is generally accepted that the ability of AMPs to kill microorganisms depends upon their capacity to bind to the membranes of these microorganisms. The ability of an AMP to interact with a target membrane depends upon its structure and the membrane target; in the case of short-chain AMPs without cysteine, the α-helical structure of the AMPs is key to achieving the interaction with the membrane target, as is the higher positive charge that is provided by the amidation of the C-terminal residue. The antimicrobial peptides evaluated in this article showed strong activity against Streptococcus sp., while exerted none effect against Burkholderia cepacia, it may be due to Streptococcus sp. is a Gram-positive bacterium, so it does not have an outer cellular membrane making it a sensitive target of the action of the AMPs. On the other hand, Burkholderia cepacia is a Gram-negative bacterium, so it has a double cell membrane representing a double barrier against the action of AMPs.
(13) Furthermore, there is a relationship of bacterial membrane lipid composition and the potency of certain antimicrobial agents. Bacteria vary widely in the lipid composition (cardiolipin, phosphatidylglycerol and phosphatidylethanolamine) of their membranes and would therefore be expected to exhibit different sensitivities to antimicrobial compounds. This may explain why the different Gram-Positive and Gram-negative bacteria evaluated in this work have a different degree of susceptibility to the peptides tested. In general, Gram-negative bacteria show higher phosphatidylethanolamine content than Gram-positive bacteria. However, Gram-positive bacteria exhibit a higher amount of anionic lipids (phosphatidylglycerol and cardiolipin). The presence of charge in the lipids favors the electrostatic interactions with cationic AMPs, followed by insertion of peptides in the lipid bilayer and then the AMPs destabilize the membrane making it permeable or disrupting it.
(14) Finally, the synergic effect of each peptide with the QnCs-BUAP peptide may be due to the fact that each combination results in a higher positive charge, which can achieve greater interaction with the lipids of the membrane and lead to destabilize it causing its rupture. The IsCT and IsCT2 peptides from the venom of the African scorpion Opisthacanthus madagascarienis were the first peptides studied of this type of AMP. Structure-function analysis of IsCT and IsCT2 revealed a linear α-helical structure. The reduced antimicrobial activity of non-amidated AMPs is due to the decrease in the positive surface charge and the structural alteration of the α-helix, which affects the ability of the AMP to disrupt the cell membrane. Synergism assays revealed the effectiveness of the combined use of the four peptides, although the mechanism of synergism remains to be elucidated. The antimicrobial peptides evaluated in this work could be valuable tools for the design and development of effective AMPs against bacteria resistant to the currently available antibiotics.8. Which item is NOT true?
Correct
Answer (E) is the right choice, you can find the items in paragraphs eight and nine. In paragraph nine it is stated that “. Previous studies have reported that three of these peptides (UyCT1, UyCT3, and UyCT5) have been effective in inhibiting a broad spectrum of bacteria…”
Incorrect
Answer (E) is the right choice, you can find the items in paragraphs eight and nine. In paragraph nine it is stated that “. Previous studies have reported that three of these peptides (UyCT1, UyCT3, and UyCT5) have been effective in inhibiting a broad spectrum of bacteria…”
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Question 9 of 17
9. Question
Structural characterization of scorpion peptides and their bactericidal activity against clinical isolates of multidrug-resistant bacteria
(1) Scorpions are arthropods belonging to the group of arachnids, which have lived on our planet for more than 400 million years. Currently, approximately 1500 species of scorpions have been described, and the study of their venoms has resulted in the discovery of a large arsenal of bioactive molecules; among these molecules, toxins are distinguished by their ability to modulate the function of diverse ion channels and membrane receptors, causing the symptoms of poisoning. Other interesting biomolecules that have been discovered in scorpion venoms are antimicrobial peptides (AMPs), which stand out for their broad-spectrum activity against Gram-positive and Gram-negative bacteria, fungi, yeast, and protozoa. The most interesting AMPs from scorpion venoms are those falling out of the Buthidae family, which do not present any risk to human health; the venoms contain antimicrobial peptides (AMPs) involved in the innate immune response of venomous arthropods. Scorpion AMPs also function as internal immune agents protecting the venom gland from infection and external immune agents cleaning saprophytic microbes from the surface of the scorpion body. In addition, synergistic effects of antimicrobial scorpion peptide and neurotoxins against bacteria has been described, which provides further evidence in favor of the multifunctionality of scorpion venom components. Most of these antimicrobial peptides do not contain disulfide bridges in their structure, known as non-disulfide-bridged peptides (NDBP), and have been classified into several groups, such as scorpine-like, long, intermediate and short-chain AMPs.
(2) Scorpine-like AMPs possess two structural and functional domains: a N-terminal α-helix (with cytolytic and/or antimicrobial activity like the insect defensins) and a tightly folded C-terminal region with a CSαβ motif, displaying K+ channel-blocking activity. The first characterized scorpine was isolated from the venom of the scorpion Pandinus imperator. This protein is formed by 75 amino acids and has shown antimicrobial activity, mainly against Bacillus subtilis, although it also has an inhibitory effect on the ookinete and gamete stages of Plasmodium berghei.
(3) Long-chain AMPs, such as hadrurin (isolated from Mexican scorpion Hadrurus aztecus), belong to the superfamily of peptides without disulfide bridges. This 41-amino acid peptide forms helical structures and has antimicrobial activity against Gram-negative bacteria, such as Salmonella typhi, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Other related peptides, such as Opistoporin-1 (Opistophthalmus carinatus) and Pandinin-1 (Pandinus imperator), both with 44 amino acids, have antimicrobial activity against Gram-positive and Gram-negative bacteria, respectively.
(4) AMPs from the scorpion Heterometrus spinifer have been reported within the group of AMPs with an intermediate size peptide chain; one of these peptides is HsAp (29 amino acids), which has broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, as well as antifungal activity; however, HsAp has limited therapeutic use because it is highly hemolytic against human erythrocytes. Other peptides included in this classification are: Heterin-2 and pandinin-2. Heterin-2 is a venom peptide from the scorpion Heterometrus spinifer which contains 24 amino acid residues. Heterin-2 is able to inhibit the growth of Gram-positive bacteria with MICs from 5.6 μM to 30.0 μM. Pandinin-2 is an α-helical polycationic antimicrobial peptide from venom of the scorpion Pandinus imperator. Pandinin-2 contains 24 amino acid residues and demonstrated high antimicrobial activity against a range of Gram-positive bacteria (2.4–5.2 μM), but was less active against Gram-negative bacteria (2.4–38.2 μM).
(5) Short-chain AMPs or IsCT-type peptides are short antimicrobial peptides derived from longer peptide precursors by post-translational processing of a signal peptide and a carboxy-terminal propeptide region that flank the mature peptide. The mature peptide contains commonly less than 20 amino acids, most of them hydrophobic.
(6) Currently, 67 IsCT-type AMPs have been reported. The first IsCT peptide was isolated from the venom of the scorpion Opisthacanthus madagascariensis; it was named in this way because the scorpion was found in Isalo (Is), Madagascar and the peptide displayed cytotoxic activity (CT). IsCT peptide presents antibacterial activity against Gram-negative and Gram-positive strains of bacteria and low hemolytic activity. Other short peptides from Mexican scorpions have also been identified, e.g., VmCT1 and VmCT2 from the scorpion Vaejovis mexicanus. From the cDNA libraries made from the venom glands of this scorpion belonging to the Vaejovidae family, the sequences of these peptides were identified. The chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity as well as low hemolytic activity. The mechanism of action of these AMPs however is unclear.
(7) Recently, as a result of the transcriptomic analysis of the venomous glands of the Urodacus yaschenkoi scorpion, the existence of a large number of peptides with potential antimicrobial activity (mainly NDBP type) was discovered. The antimicrobial activity of several of these peptides (chemically synthesized) has been evaluated e.g., the UyCT3 peptide with an amidated C-terminal showed strong antimicrobial activity, while the non-amidated UyCT3 peptide failed to exhibit any antimicrobial activity, confirming the importance of the amidation of the C-terminus. The development of new technology platforms for peptide synthesis and modification with a low cost makes peptide systems valuable tools for the design of new therapeutic weapons against multidrug-resistant (MDR) strains.
(8) The rise of MDR bacteria represents a major public health problem worldwide; consequently, global research is focused on the development of new therapeutic agents. Scorpion venoms represent an immense source of bioactive peptides, including toxins that affect the sodium channels of mammals or insects and AMPs. However, only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains. Among NDBPs with antimicrobial activity, scorpion venoms contain peptides such as Opistoporin, Pandinin or IsCT types.
(9) Urodacus yaschenkoi is an Australian scorpion that has been characterized and contains an arsenal of biomolecules with diverse functions, including AMPs. Previous studies have reported that three of these peptides (UyCT1, UyCT3 and UyCT5) have been effective in inhibiting a broad spectrum of bacteria, including MDR pathogens such as Acinetobacter baumannii, and these peptides required the amidation of the C-terminal residue to be active.
(10) Burkholderia cepacia, which is an unusual opportunistic pathogen that threatens immunocompromised patients, was resistant to all the peptides when they were tested individually, even at the highest concentrations that were evaluated. However, the combination of QnCs-BUAP with the peptides Uy234 and Uy192 displayed promising activity against Burkholderia cepacia, with MBCs of 150 μM and 300 μM, respectively. The effectiveness of peptide combinations has been reported, and different advantages of their use have been proposed, such as using lower doses, cost savings, and preventing the development of resistance. Combining the peptide QnCs-BUAP with the peptides Uy234, Uy17, and Uy192 resulted in the reduction of the MBC in almost all bacterial strains evaluated. Furthermore, a synergistic behavior was displayed in 25% of the resulting combinations, 37.5% displayed an additive effect, and only 8% showed antagonism.
(11) Some AMPs from scorpion venom have shown great potential to inhibit the growth of a broad spectrum of bacteria, including MDR clinical isolates; however, their high cytotoxicity and hemolytic activity have prevented their clinical use. According to our results, the three AMPs from U. yaschenkoi and the consensus peptide QnCs-BUAP displayed remarkably low hemolytic activity compared to that of other AMPs from scorpion venom. The hemolytic concentration (HC) of the peptides Uy17, Uy192 and Uy234 towards pig erythrocytes was previously reported with an HC25 = 26.65 μM, 35.85 μM and 55.14 μM, respectively; in our work, the same peptide sequences showed lower hemolytic activity against human erythrocytes, requiring greater peptide concentrations (> 370 μM) to achieve the same HC25.
(12) The mechanism of the antimicrobial action of these AMPs is not fully understood; however, it is generally accepted that the ability of AMPs to kill microorganisms depends upon their capacity to bind to the membranes of these microorganisms. The ability of an AMP to interact with a target membrane depends upon its structure and the membrane target; in the case of short-chain AMPs without cysteine, the α-helical structure of the AMPs is key to achieving the interaction with the membrane target, as is the higher positive charge that is provided by the amidation of the C-terminal residue. The antimicrobial peptides evaluated in this article showed strong activity against Streptococcus sp., while exerted none effect against Burkholderia cepacia, it may be due to Streptococcus sp. is a Gram-positive bacterium, so it does not have an outer cellular membrane making it a sensitive target of the action of the AMPs. On the other hand, Burkholderia cepacia is a Gram-negative bacterium, so it has a double cell membrane representing a double barrier against the action of AMPs.
(13) Furthermore, there is a relationship of bacterial membrane lipid composition and the potency of certain antimicrobial agents. Bacteria vary widely in the lipid composition (cardiolipin, phosphatidylglycerol and phosphatidylethanolamine) of their membranes and would therefore be expected to exhibit different sensitivities to antimicrobial compounds. This may explain why the different Gram-Positive and Gram-negative bacteria evaluated in this work have a different degree of susceptibility to the peptides tested. In general, Gram-negative bacteria show higher phosphatidylethanolamine content than Gram-positive bacteria. However, Gram-positive bacteria exhibit a higher amount of anionic lipids (phosphatidylglycerol and cardiolipin). The presence of charge in the lipids favors the electrostatic interactions with cationic AMPs, followed by insertion of peptides in the lipid bilayer and then the AMPs destabilize the membrane making it permeable or disrupting it.
(14) Finally, the synergic effect of each peptide with the QnCs-BUAP peptide may be due to the fact that each combination results in a higher positive charge, which can achieve greater interaction with the lipids of the membrane and lead to destabilize it causing its rupture. The IsCT and IsCT2 peptides from the venom of the African scorpion Opisthacanthus madagascarienis were the first peptides studied of this type of AMP. Structure-function analysis of IsCT and IsCT2 revealed a linear α-helical structure. The reduced antimicrobial activity of non-amidated AMPs is due to the decrease in the positive surface charge and the structural alteration of the α-helix, which affects the ability of the AMP to disrupt the cell membrane. Synergism assays revealed the effectiveness of the combined use of the four peptides, although the mechanism of synergism remains to be elucidated. The antimicrobial peptides evaluated in this work could be valuable tools for the design and development of effective AMPs against bacteria resistant to the currently available antibiotics.9. Which is an advantage that we can have by combining peptides?
Correct
Answer (D) is the right answer. In paragraph 10 the advantages of combining peptides are described and it is not stated that combining them is dangerous to human health or the results of combining peptides have not been advantageous. “The effectiveness of peptide combinations has been reported, and different advantages of their use have been proposed, such as using lower doses, cost savings, and preventing the development of resistance.”
Incorrect
Answer (D) is the right answer. In paragraph 10 the advantages of combining peptides are described and it is not stated that combining them is dangerous to human health or the results of combining peptides have not been advantageous. “The effectiveness of peptide combinations has been reported, and different advantages of their use have been proposed, such as using lower doses, cost savings, and preventing the development of resistance.”
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Question 10 of 17
10. Question
Structural characterization of scorpion peptides and their bactericidal activity against clinical isolates of multidrug-resistant bacteria
(1) Scorpions are arthropods belonging to the group of arachnids, which have lived on our planet for more than 400 million years. Currently, approximately 1500 species of scorpions have been described, and the study of their venoms has resulted in the discovery of a large arsenal of bioactive molecules; among these molecules, toxins are distinguished by their ability to modulate the function of diverse ion channels and membrane receptors, causing the symptoms of poisoning. Other interesting biomolecules that have been discovered in scorpion venoms are antimicrobial peptides (AMPs), which stand out for their broad-spectrum activity against Gram-positive and Gram-negative bacteria, fungi, yeast, and protozoa. The most interesting AMPs from scorpion venoms are those falling out of the Buthidae family, which do not present any risk to human health; the venoms contain antimicrobial peptides (AMPs) involved in the innate immune response of venomous arthropods. Scorpion AMPs also function as internal immune agents protecting the venom gland from infection and external immune agents cleaning saprophytic microbes from the surface of the scorpion body. In addition, synergistic effects of antimicrobial scorpion peptide and neurotoxins against bacteria has been described, which provides further evidence in favor of the multifunctionality of scorpion venom components. Most of these antimicrobial peptides do not contain disulfide bridges in their structure, known as non-disulfide-bridged peptides (NDBP), and have been classified into several groups, such as scorpine-like, long, intermediate and short-chain AMPs.
(2) Scorpine-like AMPs possess two structural and functional domains: a N-terminal α-helix (with cytolytic and/or antimicrobial activity like the insect defensins) and a tightly folded C-terminal region with a CSαβ motif, displaying K+ channel-blocking activity. The first characterized scorpine was isolated from the venom of the scorpion Pandinus imperator. This protein is formed by 75 amino acids and has shown antimicrobial activity, mainly against Bacillus subtilis, although it also has an inhibitory effect on the ookinete and gamete stages of Plasmodium berghei.
(3) Long-chain AMPs, such as hadrurin (isolated from Mexican scorpion Hadrurus aztecus), belong to the superfamily of peptides without disulfide bridges. This 41-amino acid peptide forms helical structures and has antimicrobial activity against Gram-negative bacteria, such as Salmonella typhi, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Other related peptides, such as Opistoporin-1 (Opistophthalmus carinatus) and Pandinin-1 (Pandinus imperator), both with 44 amino acids, have antimicrobial activity against Gram-positive and Gram-negative bacteria, respectively.
(4) AMPs from the scorpion Heterometrus spinifer have been reported within the group of AMPs with an intermediate size peptide chain; one of these peptides is HsAp (29 amino acids), which has broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, as well as antifungal activity; however, HsAp has limited therapeutic use because it is highly hemolytic against human erythrocytes. Other peptides included in this classification are: Heterin-2 and pandinin-2. Heterin-2 is a venom peptide from the scorpion Heterometrus spinifer which contains 24 amino acid residues. Heterin-2 is able to inhibit the growth of Gram-positive bacteria with MICs from 5.6 μM to 30.0 μM. Pandinin-2 is an α-helical polycationic antimicrobial peptide from venom of the scorpion Pandinus imperator. Pandinin-2 contains 24 amino acid residues and demonstrated high antimicrobial activity against a range of Gram-positive bacteria (2.4–5.2 μM), but was less active against Gram-negative bacteria (2.4–38.2 μM).
(5) Short-chain AMPs or IsCT-type peptides are short antimicrobial peptides derived from longer peptide precursors by post-translational processing of a signal peptide and a carboxy-terminal propeptide region that flank the mature peptide. The mature peptide contains commonly less than 20 amino acids, most of them hydrophobic.
(6) Currently, 67 IsCT-type AMPs have been reported. The first IsCT peptide was isolated from the venom of the scorpion Opisthacanthus madagascariensis; it was named in this way because the scorpion was found in Isalo (Is), Madagascar and the peptide displayed cytotoxic activity (CT). IsCT peptide presents antibacterial activity against Gram-negative and Gram-positive strains of bacteria and low hemolytic activity. Other short peptides from Mexican scorpions have also been identified, e.g., VmCT1 and VmCT2 from the scorpion Vaejovis mexicanus. From the cDNA libraries made from the venom glands of this scorpion belonging to the Vaejovidae family, the sequences of these peptides were identified. The chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity as well as low hemolytic activity. The mechanism of action of these AMPs however is unclear.
(7) Recently, as a result of the transcriptomic analysis of the venomous glands of the Urodacus yaschenkoi scorpion, the existence of a large number of peptides with potential antimicrobial activity (mainly NDBP type) was discovered. The antimicrobial activity of several of these peptides (chemically synthesized) has been evaluated e.g., the UyCT3 peptide with an amidated C-terminal showed strong antimicrobial activity, while the non-amidated UyCT3 peptide failed to exhibit any antimicrobial activity, confirming the importance of the amidation of the C-terminus. The development of new technology platforms for peptide synthesis and modification with a low cost makes peptide systems valuable tools for the design of new therapeutic weapons against multidrug-resistant (MDR) strains.
(8) The rise of MDR bacteria represents a major public health problem worldwide; consequently, global research is focused on the development of new therapeutic agents. Scorpion venoms represent an immense source of bioactive peptides, including toxins that affect the sodium channels of mammals or insects and AMPs. However, only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains. Among NDBPs with antimicrobial activity, scorpion venoms contain peptides such as Opistoporin, Pandinin or IsCT types.
(9) Urodacus yaschenkoi is an Australian scorpion that has been characterized and contains an arsenal of biomolecules with diverse functions, including AMPs. Previous studies have reported that three of these peptides (UyCT1, UyCT3 and UyCT5) have been effective in inhibiting a broad spectrum of bacteria, including MDR pathogens such as Acinetobacter baumannii, and these peptides required the amidation of the C-terminal residue to be active.
(10) Burkholderia cepacia, which is an unusual opportunistic pathogen that threatens immunocompromised patients, was resistant to all the peptides when they were tested individually, even at the highest concentrations that were evaluated. However, the combination of QnCs-BUAP with the peptides Uy234 and Uy192 displayed promising activity against Burkholderia cepacia, with MBCs of 150 μM and 300 μM, respectively. The effectiveness of peptide combinations has been reported, and different advantages of their use have been proposed, such as using lower doses, cost savings, and preventing the development of resistance. Combining the peptide QnCs-BUAP with the peptides Uy234, Uy17, and Uy192 resulted in the reduction of the MBC in almost all bacterial strains evaluated. Furthermore, a synergistic behavior was displayed in 25% of the resulting combinations, 37.5% displayed an additive effect, and only 8% showed antagonism.
(11) Some AMPs from scorpion venom have shown great potential to inhibit the growth of a broad spectrum of bacteria, including MDR clinical isolates; however, their high cytotoxicity and hemolytic activity have prevented their clinical use. According to our results, the three AMPs from U. yaschenkoi and the consensus peptide QnCs-BUAP displayed remarkably low hemolytic activity compared to that of other AMPs from scorpion venom. The hemolytic concentration (HC) of the peptides Uy17, Uy192 and Uy234 towards pig erythrocytes was previously reported with an HC25 = 26.65 μM, 35.85 μM and 55.14 μM, respectively; in our work, the same peptide sequences showed lower hemolytic activity against human erythrocytes, requiring greater peptide concentrations (> 370 μM) to achieve the same HC25.
(12) The mechanism of the antimicrobial action of these AMPs is not fully understood; however, it is generally accepted that the ability of AMPs to kill microorganisms depends upon their capacity to bind to the membranes of these microorganisms. The ability of an AMP to interact with a target membrane depends upon its structure and the membrane target; in the case of short-chain AMPs without cysteine, the α-helical structure of the AMPs is key to achieving the interaction with the membrane target, as is the higher positive charge that is provided by the amidation of the C-terminal residue. The antimicrobial peptides evaluated in this article showed strong activity against Streptococcus sp., while exerted none effect against Burkholderia cepacia, it may be due to Streptococcus sp. is a Gram-positive bacterium, so it does not have an outer cellular membrane making it a sensitive target of the action of the AMPs. On the other hand, Burkholderia cepacia is a Gram-negative bacterium, so it has a double cell membrane representing a double barrier against the action of AMPs.
(13) Furthermore, there is a relationship of bacterial membrane lipid composition and the potency of certain antimicrobial agents. Bacteria vary widely in the lipid composition (cardiolipin, phosphatidylglycerol and phosphatidylethanolamine) of their membranes and would therefore be expected to exhibit different sensitivities to antimicrobial compounds. This may explain why the different Gram-Positive and Gram-negative bacteria evaluated in this work have a different degree of susceptibility to the peptides tested. In general, Gram-negative bacteria show higher phosphatidylethanolamine content than Gram-positive bacteria. However, Gram-positive bacteria exhibit a higher amount of anionic lipids (phosphatidylglycerol and cardiolipin). The presence of charge in the lipids favors the electrostatic interactions with cationic AMPs, followed by insertion of peptides in the lipid bilayer and then the AMPs destabilize the membrane making it permeable or disrupting it.
(14) Finally, the synergic effect of each peptide with the QnCs-BUAP peptide may be due to the fact that each combination results in a higher positive charge, which can achieve greater interaction with the lipids of the membrane and lead to destabilize it causing its rupture. The IsCT and IsCT2 peptides from the venom of the African scorpion Opisthacanthus madagascarienis were the first peptides studied of this type of AMP. Structure-function analysis of IsCT and IsCT2 revealed a linear α-helical structure. The reduced antimicrobial activity of non-amidated AMPs is due to the decrease in the positive surface charge and the structural alteration of the α-helix, which affects the ability of the AMP to disrupt the cell membrane. Synergism assays revealed the effectiveness of the combined use of the four peptides, although the mechanism of synergism remains to be elucidated. The antimicrobial peptides evaluated in this work could be valuable tools for the design and development of effective AMPs against bacteria resistant to the currently available antibiotics.10. According to the text, what is the reason some AMPs from scorpion venom cannot be used for clinical purposes?
Correct
Answer (B) is the right choice, in paragraph eleven it is stated that “Some AMPs from scorpion venom have shown great potential to inhibit the growth of a broad spectrum of bacteria, including MDR clinical isolates; however, their high cytotoxicity and hemolytic activity have prevented their clinical use.”
Incorrect
Answer (B) is the right choice, in paragraph eleven it is stated that “Some AMPs from scorpion venom have shown great potential to inhibit the growth of a broad spectrum of bacteria, including MDR clinical isolates; however, their high cytotoxicity and hemolytic activity have prevented their clinical use.”
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Question 11 of 17
11. Question
Structural characterization of scorpion peptides and their bactericidal activity against clinical isolates of multidrug-resistant bacteria
(1) Scorpions are arthropods belonging to the group of arachnids, which have lived on our planet for more than 400 million years. Currently, approximately 1500 species of scorpions have been described, and the study of their venoms has resulted in the discovery of a large arsenal of bioactive molecules; among these molecules, toxins are distinguished by their ability to modulate the function of diverse ion channels and membrane receptors, causing the symptoms of poisoning. Other interesting biomolecules that have been discovered in scorpion venoms are antimicrobial peptides (AMPs), which stand out for their broad-spectrum activity against Gram-positive and Gram-negative bacteria, fungi, yeast, and protozoa. The most interesting AMPs from scorpion venoms are those falling out of the Buthidae family, which do not present any risk to human health; the venoms contain antimicrobial peptides (AMPs) involved in the innate immune response of venomous arthropods. Scorpion AMPs also function as internal immune agents protecting the venom gland from infection and external immune agents cleaning saprophytic microbes from the surface of the scorpion body. In addition, synergistic effects of antimicrobial scorpion peptide and neurotoxins against bacteria has been described, which provides further evidence in favor of the multifunctionality of scorpion venom components. Most of these antimicrobial peptides do not contain disulfide bridges in their structure, known as non-disulfide-bridged peptides (NDBP), and have been classified into several groups, such as scorpine-like, long, intermediate and short-chain AMPs.
(2) Scorpine-like AMPs possess two structural and functional domains: a N-terminal α-helix (with cytolytic and/or antimicrobial activity like the insect defensins) and a tightly folded C-terminal region with a CSαβ motif, displaying K+ channel-blocking activity. The first characterized scorpine was isolated from the venom of the scorpion Pandinus imperator. This protein is formed by 75 amino acids and has shown antimicrobial activity, mainly against Bacillus subtilis, although it also has an inhibitory effect on the ookinete and gamete stages of Plasmodium berghei.
(3) Long-chain AMPs, such as hadrurin (isolated from Mexican scorpion Hadrurus aztecus), belong to the superfamily of peptides without disulfide bridges. This 41-amino acid peptide forms helical structures and has antimicrobial activity against Gram-negative bacteria, such as Salmonella typhi, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Other related peptides, such as Opistoporin-1 (Opistophthalmus carinatus) and Pandinin-1 (Pandinus imperator), both with 44 amino acids, have antimicrobial activity against Gram-positive and Gram-negative bacteria, respectively.
(4) AMPs from the scorpion Heterometrus spinifer have been reported within the group of AMPs with an intermediate size peptide chain; one of these peptides is HsAp (29 amino acids), which has broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, as well as antifungal activity; however, HsAp has limited therapeutic use because it is highly hemolytic against human erythrocytes. Other peptides included in this classification are: Heterin-2 and pandinin-2. Heterin-2 is a venom peptide from the scorpion Heterometrus spinifer which contains 24 amino acid residues. Heterin-2 is able to inhibit the growth of Gram-positive bacteria with MICs from 5.6 μM to 30.0 μM. Pandinin-2 is an α-helical polycationic antimicrobial peptide from venom of the scorpion Pandinus imperator. Pandinin-2 contains 24 amino acid residues and demonstrated high antimicrobial activity against a range of Gram-positive bacteria (2.4–5.2 μM), but was less active against Gram-negative bacteria (2.4–38.2 μM).
(5) Short-chain AMPs or IsCT-type peptides are short antimicrobial peptides derived from longer peptide precursors by post-translational processing of a signal peptide and a carboxy-terminal propeptide region that flank the mature peptide. The mature peptide contains commonly less than 20 amino acids, most of them hydrophobic.
(6) Currently, 67 IsCT-type AMPs have been reported. The first IsCT peptide was isolated from the venom of the scorpion Opisthacanthus madagascariensis; it was named in this way because the scorpion was found in Isalo (Is), Madagascar and the peptide displayed cytotoxic activity (CT). IsCT peptide presents antibacterial activity against Gram-negative and Gram-positive strains of bacteria and low hemolytic activity. Other short peptides from Mexican scorpions have also been identified, e.g., VmCT1 and VmCT2 from the scorpion Vaejovis mexicanus. From the cDNA libraries made from the venom glands of this scorpion belonging to the Vaejovidae family, the sequences of these peptides were identified. The chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity as well as low hemolytic activity. The mechanism of action of these AMPs however is unclear.
(7) Recently, as a result of the transcriptomic analysis of the venomous glands of the Urodacus yaschenkoi scorpion, the existence of a large number of peptides with potential antimicrobial activity (mainly NDBP type) was discovered. The antimicrobial activity of several of these peptides (chemically synthesized) has been evaluated e.g., the UyCT3 peptide with an amidated C-terminal showed strong antimicrobial activity, while the non-amidated UyCT3 peptide failed to exhibit any antimicrobial activity, confirming the importance of the amidation of the C-terminus. The development of new technology platforms for peptide synthesis and modification with a low cost makes peptide systems valuable tools for the design of new therapeutic weapons against multidrug-resistant (MDR) strains.
(8) The rise of MDR bacteria represents a major public health problem worldwide; consequently, global research is focused on the development of new therapeutic agents. Scorpion venoms represent an immense source of bioactive peptides, including toxins that affect the sodium channels of mammals or insects and AMPs. However, only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains. Among NDBPs with antimicrobial activity, scorpion venoms contain peptides such as Opistoporin, Pandinin or IsCT types.
(9) Urodacus yaschenkoi is an Australian scorpion that has been characterized and contains an arsenal of biomolecules with diverse functions, including AMPs. Previous studies have reported that three of these peptides (UyCT1, UyCT3 and UyCT5) have been effective in inhibiting a broad spectrum of bacteria, including MDR pathogens such as Acinetobacter baumannii, and these peptides required the amidation of the C-terminal residue to be active.
(10) Burkholderia cepacia, which is an unusual opportunistic pathogen that threatens immunocompromised patients, was resistant to all the peptides when they were tested individually, even at the highest concentrations that were evaluated. However, the combination of QnCs-BUAP with the peptides Uy234 and Uy192 displayed promising activity against Burkholderia cepacia, with MBCs of 150 μM and 300 μM, respectively. The effectiveness of peptide combinations has been reported, and different advantages of their use have been proposed, such as using lower doses, cost savings, and preventing the development of resistance. Combining the peptide QnCs-BUAP with the peptides Uy234, Uy17, and Uy192 resulted in the reduction of the MBC in almost all bacterial strains evaluated. Furthermore, a synergistic behavior was displayed in 25% of the resulting combinations, 37.5% displayed an additive effect, and only 8% showed antagonism.
(11) Some AMPs from scorpion venom have shown great potential to inhibit the growth of a broad spectrum of bacteria, including MDR clinical isolates; however, their high cytotoxicity and hemolytic activity have prevented their clinical use. According to our results, the three AMPs from U. yaschenkoi and the consensus peptide QnCs-BUAP displayed remarkably low hemolytic activity compared to that of other AMPs from scorpion venom. The hemolytic concentration (HC) of the peptides Uy17, Uy192 and Uy234 towards pig erythrocytes was previously reported with an HC25 = 26.65 μM, 35.85 μM and 55.14 μM, respectively; in our work, the same peptide sequences showed lower hemolytic activity against human erythrocytes, requiring greater peptide concentrations (> 370 μM) to achieve the same HC25.
(12) The mechanism of the antimicrobial action of these AMPs is not fully understood; however, it is generally accepted that the ability of AMPs to kill microorganisms depends upon their capacity to bind to the membranes of these microorganisms. The ability of an AMP to interact with a target membrane depends upon its structure and the membrane target; in the case of short-chain AMPs without cysteine, the α-helical structure of the AMPs is key to achieving the interaction with the membrane target, as is the higher positive charge that is provided by the amidation of the C-terminal residue. The antimicrobial peptides evaluated in this article showed strong activity against Streptococcus sp., while exerted none effect against Burkholderia cepacia, it may be due to Streptococcus sp. is a Gram-positive bacterium, so it does not have an outer cellular membrane making it a sensitive target of the action of the AMPs. On the other hand, Burkholderia cepacia is a Gram-negative bacterium, so it has a double cell membrane representing a double barrier against the action of AMPs.
(13) Furthermore, there is a relationship of bacterial membrane lipid composition and the potency of certain antimicrobial agents. Bacteria vary widely in the lipid composition (cardiolipin, phosphatidylglycerol and phosphatidylethanolamine) of their membranes and would therefore be expected to exhibit different sensitivities to antimicrobial compounds. This may explain why the different Gram-Positive and Gram-negative bacteria evaluated in this work have a different degree of susceptibility to the peptides tested. In general, Gram-negative bacteria show higher phosphatidylethanolamine content than Gram-positive bacteria. However, Gram-positive bacteria exhibit a higher amount of anionic lipids (phosphatidylglycerol and cardiolipin). The presence of charge in the lipids favors the electrostatic interactions with cationic AMPs, followed by insertion of peptides in the lipid bilayer and then the AMPs destabilize the membrane making it permeable or disrupting it.
(14) Finally, the synergic effect of each peptide with the QnCs-BUAP peptide may be due to the fact that each combination results in a higher positive charge, which can achieve greater interaction with the lipids of the membrane and lead to destabilize it causing its rupture. The IsCT and IsCT2 peptides from the venom of the African scorpion Opisthacanthus madagascarienis were the first peptides studied of this type of AMP. Structure-function analysis of IsCT and IsCT2 revealed a linear α-helical structure. The reduced antimicrobial activity of non-amidated AMPs is due to the decrease in the positive surface charge and the structural alteration of the α-helix, which affects the ability of the AMP to disrupt the cell membrane. Synergism assays revealed the effectiveness of the combined use of the four peptides, although the mechanism of synergism remains to be elucidated. The antimicrobial peptides evaluated in this work could be valuable tools for the design and development of effective AMPs against bacteria resistant to the currently available antibiotics.11. The capacity of AMPs to bind to the membranes of microorganisms contributes to …
Correct
Answer (A) is the right choice, in paragraph twelve it is stated that “the ability of AMPs to kill microorganisms depends upon their capacity to bind to the membranes of these microorganisms”.
Incorrect
Answer (A) is the right choice, in paragraph twelve it is stated that “the ability of AMPs to kill microorganisms depends upon their capacity to bind to the membranes of these microorganisms”.
-
Question 12 of 17
12. Question
Structural characterization of scorpion peptides and their bactericidal activity against clinical isolates of multidrug-resistant bacteria
(1) Scorpions are arthropods belonging to the group of arachnids, which have lived on our planet for more than 400 million years. Currently, approximately 1500 species of scorpions have been described, and the study of their venoms has resulted in the discovery of a large arsenal of bioactive molecules; among these molecules, toxins are distinguished by their ability to modulate the function of diverse ion channels and membrane receptors, causing the symptoms of poisoning. Other interesting biomolecules that have been discovered in scorpion venoms are antimicrobial peptides (AMPs), which stand out for their broad-spectrum activity against Gram-positive and Gram-negative bacteria, fungi, yeast, and protozoa. The most interesting AMPs from scorpion venoms are those falling out of the Buthidae family, which do not present any risk to human health; the venoms contain antimicrobial peptides (AMPs) involved in the innate immune response of venomous arthropods. Scorpion AMPs also function as internal immune agents protecting the venom gland from infection and external immune agents cleaning saprophytic microbes from the surface of the scorpion body. In addition, synergistic effects of antimicrobial scorpion peptide and neurotoxins against bacteria has been described, which provides further evidence in favor of the multifunctionality of scorpion venom components. Most of these antimicrobial peptides do not contain disulfide bridges in their structure, known as non-disulfide-bridged peptides (NDBP), and have been classified into several groups, such as scorpine-like, long, intermediate and short-chain AMPs.
(2) Scorpine-like AMPs possess two structural and functional domains: a N-terminal α-helix (with cytolytic and/or antimicrobial activity like the insect defensins) and a tightly folded C-terminal region with a CSαβ motif, displaying K+ channel-blocking activity. The first characterized scorpine was isolated from the venom of the scorpion Pandinus imperator. This protein is formed by 75 amino acids and has shown antimicrobial activity, mainly against Bacillus subtilis, although it also has an inhibitory effect on the ookinete and gamete stages of Plasmodium berghei.
(3) Long-chain AMPs, such as hadrurin (isolated from Mexican scorpion Hadrurus aztecus), belong to the superfamily of peptides without disulfide bridges. This 41-amino acid peptide forms helical structures and has antimicrobial activity against Gram-negative bacteria, such as Salmonella typhi, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Other related peptides, such as Opistoporin-1 (Opistophthalmus carinatus) and Pandinin-1 (Pandinus imperator), both with 44 amino acids, have antimicrobial activity against Gram-positive and Gram-negative bacteria, respectively.
(4) AMPs from the scorpion Heterometrus spinifer have been reported within the group of AMPs with an intermediate size peptide chain; one of these peptides is HsAp (29 amino acids), which has broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, as well as antifungal activity; however, HsAp has limited therapeutic use because it is highly hemolytic against human erythrocytes. Other peptides included in this classification are: Heterin-2 and pandinin-2. Heterin-2 is a venom peptide from the scorpion Heterometrus spinifer which contains 24 amino acid residues. Heterin-2 is able to inhibit the growth of Gram-positive bacteria with MICs from 5.6 μM to 30.0 μM. Pandinin-2 is an α-helical polycationic antimicrobial peptide from venom of the scorpion Pandinus imperator. Pandinin-2 contains 24 amino acid residues and demonstrated high antimicrobial activity against a range of Gram-positive bacteria (2.4–5.2 μM), but was less active against Gram-negative bacteria (2.4–38.2 μM).
(5) Short-chain AMPs or IsCT-type peptides are short antimicrobial peptides derived from longer peptide precursors by post-translational processing of a signal peptide and a carboxy-terminal propeptide region that flank the mature peptide. The mature peptide contains commonly less than 20 amino acids, most of them hydrophobic.
(6) Currently, 67 IsCT-type AMPs have been reported. The first IsCT peptide was isolated from the venom of the scorpion Opisthacanthus madagascariensis; it was named in this way because the scorpion was found in Isalo (Is), Madagascar and the peptide displayed cytotoxic activity (CT). IsCT peptide presents antibacterial activity against Gram-negative and Gram-positive strains of bacteria and low hemolytic activity. Other short peptides from Mexican scorpions have also been identified, e.g., VmCT1 and VmCT2 from the scorpion Vaejovis mexicanus. From the cDNA libraries made from the venom glands of this scorpion belonging to the Vaejovidae family, the sequences of these peptides were identified. The chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity as well as low hemolytic activity. The mechanism of action of these AMPs however is unclear.
(7) Recently, as a result of the transcriptomic analysis of the venomous glands of the Urodacus yaschenkoi scorpion, the existence of a large number of peptides with potential antimicrobial activity (mainly NDBP type) was discovered. The antimicrobial activity of several of these peptides (chemically synthesized) has been evaluated e.g., the UyCT3 peptide with an amidated C-terminal showed strong antimicrobial activity, while the non-amidated UyCT3 peptide failed to exhibit any antimicrobial activity, confirming the importance of the amidation of the C-terminus. The development of new technology platforms for peptide synthesis and modification with a low cost makes peptide systems valuable tools for the design of new therapeutic weapons against multidrug-resistant (MDR) strains.
(8) The rise of MDR bacteria represents a major public health problem worldwide; consequently, global research is focused on the development of new therapeutic agents. Scorpion venoms represent an immense source of bioactive peptides, including toxins that affect the sodium channels of mammals or insects and AMPs. However, only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains. Among NDBPs with antimicrobial activity, scorpion venoms contain peptides such as Opistoporin, Pandinin or IsCT types.
(9) Urodacus yaschenkoi is an Australian scorpion that has been characterized and contains an arsenal of biomolecules with diverse functions, including AMPs. Previous studies have reported that three of these peptides (UyCT1, UyCT3 and UyCT5) have been effective in inhibiting a broad spectrum of bacteria, including MDR pathogens such as Acinetobacter baumannii, and these peptides required the amidation of the C-terminal residue to be active.
(10) Burkholderia cepacia, which is an unusual opportunistic pathogen that threatens immunocompromised patients, was resistant to all the peptides when they were tested individually, even at the highest concentrations that were evaluated. However, the combination of QnCs-BUAP with the peptides Uy234 and Uy192 displayed promising activity against Burkholderia cepacia, with MBCs of 150 μM and 300 μM, respectively. The effectiveness of peptide combinations has been reported, and different advantages of their use have been proposed, such as using lower doses, cost savings, and preventing the development of resistance. Combining the peptide QnCs-BUAP with the peptides Uy234, Uy17, and Uy192 resulted in the reduction of the MBC in almost all bacterial strains evaluated. Furthermore, a synergistic behavior was displayed in 25% of the resulting combinations, 37.5% displayed an additive effect, and only 8% showed antagonism.
(11) Some AMPs from scorpion venom have shown great potential to inhibit the growth of a broad spectrum of bacteria, including MDR clinical isolates; however, their high cytotoxicity and hemolytic activity have prevented their clinical use. According to our results, the three AMPs from U. yaschenkoi and the consensus peptide QnCs-BUAP displayed remarkably low hemolytic activity compared to that of other AMPs from scorpion venom. The hemolytic concentration (HC) of the peptides Uy17, Uy192 and Uy234 towards pig erythrocytes was previously reported with an HC25 = 26.65 μM, 35.85 μM and 55.14 μM, respectively; in our work, the same peptide sequences showed lower hemolytic activity against human erythrocytes, requiring greater peptide concentrations (> 370 μM) to achieve the same HC25.
(12) The mechanism of the antimicrobial action of these AMPs is not fully understood; however, it is generally accepted that the ability of AMPs to kill microorganisms depends upon their capacity to bind to the membranes of these microorganisms. The ability of an AMP to interact with a target membrane depends upon its structure and the membrane target; in the case of short-chain AMPs without cysteine, the α-helical structure of the AMPs is key to achieving the interaction with the membrane target, as is the higher positive charge that is provided by the amidation of the C-terminal residue. The antimicrobial peptides evaluated in this article showed strong activity against Streptococcus sp., while exerted none effect against Burkholderia cepacia, it may be due to Streptococcus sp. is a Gram-positive bacterium, so it does not have an outer cellular membrane making it a sensitive target of the action of the AMPs. On the other hand, Burkholderia cepacia is a Gram-negative bacterium, so it has a double cell membrane representing a double barrier against the action of AMPs.
(13) Furthermore, there is a relationship of bacterial membrane lipid composition and the potency of certain antimicrobial agents. Bacteria vary widely in the lipid composition (cardiolipin, phosphatidylglycerol, and phosphatidylethanolamine) of their membranes and would, therefore, be expected to exhibit different sensitivities to antimicrobial compounds. This may explain why the different Gram-Positive and Gram-negative bacteria evaluated in this work have a different degree of susceptibility to the peptides tested. In general, Gram-negative bacteria show higher phosphatidylethanolamine content than Gram-positive bacteria. However, Gram-positive bacteria exhibit a higher amount of anionic lipids (phosphatidylglycerol and cardiolipin). The presence of charge in the lipids favors the electrostatic interactions with cationic AMPs, followed by insertion of peptides in the lipid bilayer and then the AMPs destabilize the membrane making it permeable or disrupting it.
(14) Finally, the synergic effect of each peptide with the QnCs-BUAP peptide may be due to the fact that each combination results in a higher positive charge, which can achieve greater interaction with the lipids of the membrane and lead to destabilize it causing its rupture. The IsCT and IsCT2 peptides from the venom of the African scorpion Opisthacanthus madagascarienis were the first peptides studied of this type of AMP. Structure-function analysis of IsCT and IsCT2 revealed a linear α-helical structure. The reduced antimicrobial activity of non-amidated AMPs is due to the decrease in the positive surface charge and the structural alteration of the α-helix, which affects the ability of the AMP to disrupt the cell membrane. Synergism assays revealed the effectiveness of the combined use of the four peptides, although the mechanism of synergism remains to be elucidated. The antimicrobial peptides evaluated in this work could be valuable tools for the design and development of effective AMPs against bacteria resistant to the currently available antibiotics.12. Which item is possibly a result of various bacterial membrane lipid compositions?
Correct
Answer (B) is the right answer. In paragraph thirteen it is stated that “Bacteria vary widely in the lipid composition of their membranes and would, therefore, be expected to exhibit different sensitivities to antimicrobial compounds.” Notice this does not mean item A is the result of various bacterial membrane lipid composition, the same applies for options C and D since being susceptible to peptides is not a possible result of the existence of various bacterial membrane lipid compositions.
Incorrect
Answer (B) is the right answer. In paragraph thirteen it is stated that “Bacteria vary widely in the lipid composition of their membranes and would, therefore, be expected to exhibit different sensitivities to antimicrobial compounds.” Notice this does not mean item A is the result of various bacterial membrane lipid composition, the same applies for options C and D since being susceptible to peptides is not a possible result of the existence of various bacterial membrane lipid compositions.
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Question 13 of 17
13. Question
Structural characterization of scorpion peptides and their bactericidal activity against clinical isolates of multidrug-resistant bacteria
(1) Scorpions are arthropods belonging to the group of arachnids, which have lived on our planet for more than 400 million years. Currently, approximately 1500 species of scorpions have been described, and the study of their venoms has resulted in the discovery of a large arsenal of bioactive molecules; among these molecules, toxins are distinguished by their ability to modulate the function of diverse ion channels and membrane receptors, causing the symptoms of poisoning. Other interesting biomolecules that have been discovered in scorpion venoms are antimicrobial peptides (AMPs), which stand out for their broad-spectrum activity against Gram-positive and Gram-negative bacteria, fungi, yeast, and protozoa. The most interesting AMPs from scorpion venoms are those falling out of the Buthidae family, which do not present any risk to human health; the venoms contain antimicrobial peptides (AMPs) involved in the innate immune response of venomous arthropods. Scorpion AMPs also function as internal immune agents protecting the venom gland from infection and external immune agents cleaning saprophytic microbes from the surface of the scorpion body. In addition, synergistic effects of antimicrobial scorpion peptide and neurotoxins against bacteria has been described, which provides further evidence in favor of the multifunctionality of scorpion venom components. Most of these antimicrobial peptides do not contain disulfide bridges in their structure, known as non-disulfide-bridged peptides (NDBP), and have been classified into several groups, such as scorpine-like, long, intermediate and short-chain AMPs.
(2) Scorpine-like AMPs possess two structural and functional domains: a N-terminal α-helix (with cytolytic and/or antimicrobial activity like the insect defensins) and a tightly folded C-terminal region with a CSαβ motif, displaying K+ channel-blocking activity. The first characterized scorpine was isolated from the venom of the scorpion Pandinus imperator. This protein is formed by 75 amino acids and has shown antimicrobial activity, mainly against Bacillus subtilis, although it also has an inhibitory effect on the ookinete and gamete stages of Plasmodium berghei.
(3) Long-chain AMPs, such as hadrurin (isolated from Mexican scorpion Hadrurus aztecus), belong to the superfamily of peptides without disulfide bridges. This 41-amino acid peptide forms helical structures and has antimicrobial activity against Gram-negative bacteria, such as Salmonella typhi, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Other related peptides, such as Opistoporin-1 (Opistophthalmus carinatus) and Pandinin-1 (Pandinus imperator), both with 44 amino acids, have antimicrobial activity against Gram-positive and Gram-negative bacteria, respectively.
(4) AMPs from the scorpion Heterometrus spinifer have been reported within the group of AMPs with an intermediate size peptide chain; one of these peptides is HsAp (29 amino acids), which has broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, as well as antifungal activity; however, HsAp has limited therapeutic use because it is highly hemolytic against human erythrocytes. Other peptides included in this classification are: Heterin-2 and pandinin-2. Heterin-2 is a venom peptide from the scorpion Heterometrus spinifer which contains 24 amino acid residues. Heterin-2 is able to inhibit the growth of Gram-positive bacteria with MICs from 5.6 μM to 30.0 μM. Pandinin-2 is an α-helical polycationic antimicrobial peptide from venom of the scorpion Pandinus imperator. Pandinin-2 contains 24 amino acid residues and demonstrated high antimicrobial activity against a range of Gram-positive bacteria (2.4–5.2 μM), but was less active against Gram-negative bacteria (2.4–38.2 μM).
(5) Short-chain AMPs or IsCT-type peptides are short antimicrobial peptides derived from longer peptide precursors by post-translational processing of a signal peptide and a carboxy-terminal propeptide region that flank the mature peptide. The mature peptide contains commonly less than 20 amino acids, most of them hydrophobic.
(6) Currently, 67 IsCT-type AMPs have been reported. The first IsCT peptide was isolated from the venom of the scorpion Opisthacanthus madagascariensis; it was named in this way because the scorpion was found in Isalo (Is), Madagascar and the peptide displayed cytotoxic activity (CT). IsCT peptide presents antibacterial activity against Gram-negative and Gram-positive strains of bacteria and low hemolytic activity. Other short peptides from Mexican scorpions have also been identified, e.g., VmCT1 and VmCT2 from the scorpion Vaejovis mexicanus. From the cDNA libraries made from the venom glands of this scorpion belonging to the Vaejovidae family, the sequences of these peptides were identified. The chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity as well as low hemolytic activity. The mechanism of action of these AMPs however is unclear.
(7) Recently, as a result of the transcriptomic analysis of the venomous glands of the Urodacus yaschenkoi scorpion, the existence of a large number of peptides with potential antimicrobial activity (mainly NDBP type) was discovered. The antimicrobial activity of several of these peptides (chemically synthesized) has been evaluated e.g., the UyCT3 peptide with an amidated C-terminal showed strong antimicrobial activity, while the non-amidated UyCT3 peptide failed to exhibit any antimicrobial activity, confirming the importance of the amidation of the C-terminus. The development of new technology platforms for peptide synthesis and modification with a low cost makes peptide systems valuable tools for the design of new therapeutic weapons against multidrug-resistant (MDR) strains.
(8) The rise of MDR bacteria represents a major public health problem worldwide; consequently, global research is focused on the development of new therapeutic agents. Scorpion venoms represent an immense source of bioactive peptides, including toxins that affect the sodium channels of mammals or insects and AMPs. However, only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains. Among NDBPs with antimicrobial activity, scorpion venoms contain peptides such as Opistoporin, Pandinin or IsCT types.
(9) Urodacus yaschenkoi is an Australian scorpion that has been characterized and contains an arsenal of biomolecules with diverse functions, including AMPs. Previous studies have reported that three of these peptides (UyCT1, UyCT3, and UyCT5) have been effective in inhibiting a broad spectrum of bacteria, including MDR pathogens such as Acinetobacter baumannii, and these peptides required the amidation of the C-terminal residue to be active.
(10) Burkholderia cepacia, which is an unusual opportunistic pathogen that threatens immunocompromised patients, was resistant to all the peptides when they were tested individually, even at the highest concentrations that were evaluated. However, the combination of QnCs-BUAP with the peptides Uy234 and Uy192 displayed promising activity against Burkholderia cepacia, with MBCs of 150 μM and 300 μM, respectively. The effectiveness of peptide combinations has been reported, and different advantages of their use have been proposed, such as using lower doses, cost savings, and preventing the development of resistance. Combining the peptide QnCs-BUAP with the peptides Uy234, Uy17, and Uy192 resulted in the reduction of the MBC in almost all bacterial strains evaluated. Furthermore, a synergistic behavior was displayed in 25% of the resulting combinations, 37.5% displayed an additive effect, and only 8% showed antagonism.
(11) Some AMPs from scorpion venom have shown great potential to inhibit the growth of a broad spectrum of bacteria, including MDR clinical isolates; however, their high cytotoxicity and hemolytic activity have prevented their clinical use. According to our results, the three AMPs from U. yaschenkoi and the consensus peptide QnCs-BUAP displayed remarkably low hemolytic activity compared to that of other AMPs from scorpion venom. The hemolytic concentration (HC) of the peptides Uy17, Uy192 and Uy234 towards pig erythrocytes was previously reported with an HC25 = 26.65 μM, 35.85 μM and 55.14 μM, respectively; in our work, the same peptide sequences showed lower hemolytic activity against human erythrocytes, requiring greater peptide concentrations (> 370 μM) to achieve the same HC25.
(12) The mechanism of the antimicrobial action of these AMPs is not fully understood; however, it is generally accepted that the ability of AMPs to kill microorganisms depends upon their capacity to bind to the membranes of these microorganisms. The ability of an AMP to interact with a target membrane depends upon its structure and the membrane target; in the case of short-chain AMPs without cysteine, the α-helical structure of the AMPs is key to achieving the interaction with the membrane target, as is the higher positive charge that is provided by the amidation of the C-terminal residue. The antimicrobial peptides evaluated in this article showed strong activity against Streptococcus sp., while exerted none effect against Burkholderia cepacia, it may be due to Streptococcus sp. is a Gram-positive bacterium, so it does not have an outer cellular membrane making it a sensitive target of the action of the AMPs. On the other hand, Burkholderia cepacia is a Gram-negative bacterium, so it has a double cell membrane representing a double barrier against the action of AMPs.
(13) Furthermore, there is a relationship of bacterial membrane lipid composition and the potency of certain antimicrobial agents. Bacteria vary widely in the lipid composition (cardiolipin, phosphatidylglycerol and phosphatidylethanolamine) of their membranes and would, therefore, be expected to exhibit different sensitivities to antimicrobial compounds. This may explain why the different Gram-Positive and Gram-negative bacteria evaluated in this work have a different degree of susceptibility to the peptides tested. In general, Gram-negative bacteria show higher phosphatidylethanolamine content than Gram-positive bacteria. However, Gram-positive bacteria exhibit a higher amount of anionic lipids (phosphatidylglycerol and cardiolipin). The presence of charge in the lipids favors the electrostatic interactions with cationic AMPs, followed by insertion of peptides in the lipid bilayer and then the AMPs destabilize the membrane making it permeable or disrupting it.
(14) Finally, the synergic effect of each peptide with the QnCs-BUAP peptide may be due to the fact that each combination results in a higher positive charge, which can achieve greater interaction with the lipids of the membrane and lead to destabilize it causing its rupture. The IsCT and IsCT2 peptides from the venom of the African scorpion Opisthacanthus madagascarienis were the first peptides studied of this type of AMP. Structure-function analysis of IsCT and IsCT2 revealed a linear α-helical structure. The reduced antimicrobial activity of non-amidated AMPs is due to the decrease in the positive surface charge and the structural alteration of the α-helix, which affects the ability of the AMP to disrupt the cell membrane. Synergism assays revealed the effectiveness of the combined use of the four peptides, although the mechanism of synergism remains to be elucidated. The antimicrobial peptides evaluated in this work could be valuable tools for the design and development of effective AMPs against bacteria resistant to the currently available antibiotics.13. Gram-negative bacteria show higher phosphatidylethanolamine content than Gram-positive bacteria.
Gram-positive bacteria exhibit a higher amount of anionic lipids.Correct
Answer (B) is the correct choice. In the middle of paragraph thirteen, you can find these statements to be true.
Incorrect
Answer (B) is the correct choice. In the middle of paragraph thirteen, you can find these statements to be true.
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Question 14 of 17
14. Question
Structural characterization of scorpion peptides and their bactericidal activity against clinical isolates of multidrug-resistant bacteria
(1) Scorpions are arthropods belonging to the group of arachnids, which have lived on our planet for more than 400 million years. Currently, approximately 1500 species of scorpions have been described, and the study of their venoms has resulted in the discovery of a large arsenal of bioactive molecules; among these molecules, toxins are distinguished by their ability to modulate the function of diverse ion channels and membrane receptors, causing the symptoms of poisoning. Other interesting biomolecules that have been discovered in scorpion venoms are antimicrobial peptides (AMPs), which stand out for their broad-spectrum activity against Gram-positive and Gram-negative bacteria, fungi, yeast, and protozoa. The most interesting AMPs from scorpion venoms are those falling out of the Buthidae family, which do not present any risk to human health; the venoms contain antimicrobial peptides (AMPs) involved in the innate immune response of venomous arthropods. Scorpion AMPs also function as internal immune agents protecting the venom gland from infection and external immune agents cleaning saprophytic microbes from the surface of the scorpion body. In addition, synergistic effects of antimicrobial scorpion peptide and neurotoxins against bacteria has been described, which provides further evidence in favor of the multifunctionality of scorpion venom components. Most of these antimicrobial peptides do not contain disulfide bridges in their structure, known as non-disulfide-bridged peptides (NDBP), and have been classified into several groups, such as scorpine-like, long, intermediate and short-chain AMPs.
(2) Scorpine-like AMPs possess two structural and functional domains: a N-terminal α-helix (with cytolytic and/or antimicrobial activity like the insect defensins) and a tightly folded C-terminal region with a CSαβ motif, displaying K+ channel-blocking activity. The first characterized scorpine was isolated from the venom of the scorpion Pandinus imperator. This protein is formed by 75 amino acids and has shown antimicrobial activity, mainly against Bacillus subtilis, although it also has an inhibitory effect on the ookinete and gamete stages of Plasmodium berghei.
(3) Long-chain AMPs, such as hadrurin (isolated from Mexican scorpion Hadrurus aztecus), belong to the superfamily of peptides without disulfide bridges. This 41-amino acid peptide forms helical structures and has antimicrobial activity against Gram-negative bacteria, such as Salmonella typhi, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Other related peptides, such as Opistoporin-1 (Opistophthalmus carinatus) and Pandinin-1 (Pandinus imperator), both with 44 amino acids, have antimicrobial activity against Gram-positive and Gram-negative bacteria, respectively.
(4) AMPs from the scorpion Heterometrus spinifer have been reported within the group of AMPs with an intermediate size peptide chain; one of these peptides is HsAp (29 amino acids), which has broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, as well as antifungal activity; however, HsAp has limited therapeutic use because it is highly hemolytic against human erythrocytes. Other peptides included in this classification are: Heterin-2 and pandinin-2. Heterin-2 is a venom peptide from the scorpion Heterometrus spinifer which contains 24 amino acid residues. Heterin-2 is able to inhibit the growth of Gram-positive bacteria with MICs from 5.6 μM to 30.0 μM. Pandinin-2 is an α-helical polycationic antimicrobial peptide from venom of the scorpion Pandinus imperator. Pandinin-2 contains 24 amino acid residues and demonstrated high antimicrobial activity against a range of Gram-positive bacteria (2.4–5.2 μM), but was less active against Gram-negative bacteria (2.4–38.2 μM).
(5) Short-chain AMPs or IsCT-type peptides are short antimicrobial peptides derived from longer peptide precursors by post-translational processing of a signal peptide and a carboxy-terminal propeptide region that flank the mature peptide. The mature peptide contains commonly less than 20 amino acids, most of them hydrophobic.
(6) Currently, 67 IsCT-type AMPs have been reported. The first IsCT peptide was isolated from the venom of the scorpion Opisthacanthus madagascariensis; it was named in this way because the scorpion was found in Isalo (Is), Madagascar and the peptide displayed cytotoxic activity (CT). IsCT peptide presents antibacterial activity against Gram-negative and Gram-positive strains of bacteria and low hemolytic activity. Other short peptides from Mexican scorpions have also been identified, e.g., VmCT1 and VmCT2 from the scorpion Vaejovis mexicanus. From the cDNA libraries made from the venom glands of this scorpion belonging to the Vaejovidae family, the sequences of these peptides were identified. The chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity as well as low hemolytic activity. The mechanism of action of these AMPs however is unclear.
(7) Recently, as a result of the transcriptomic analysis of the venomous glands of the Urodacus yaschenkoi scorpion, the existence of a large number of peptides with potential antimicrobial activity (mainly NDBP type) was discovered. The antimicrobial activity of several of these peptides (chemically synthesized) has been evaluated e.g., the UyCT3 peptide with an amidated C-terminal showed strong antimicrobial activity, while the non-amidated UyCT3 peptide failed to exhibit any antimicrobial activity, confirming the importance of the amidation of the C-terminus. The development of new technology platforms for peptide synthesis and modification with a low cost makes peptide systems valuable tools for the design of new therapeutic weapons against multidrug-resistant (MDR) strains.
(8) The rise of MDR bacteria represents a major public health problem worldwide; consequently, global research is focused on the development of new therapeutic agents. Scorpion venoms represent an immense source of bioactive peptides, including toxins that affect the sodium channels of mammals or insects and AMPs. However, only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains. Among NDBPs with antimicrobial activity, scorpion venoms contain peptides such as Opistoporin, Pandinin or IsCT types.
(9) Urodacus yaschenkoi is an Australian scorpion that has been characterized and contains an arsenal of biomolecules with diverse functions, including AMPs. Previous studies have reported that three of these peptides (UyCT1, UyCT3, and UyCT5) have been effective in inhibiting a broad spectrum of bacteria, including MDR pathogens such as Acinetobacter baumannii, and these peptides required the amidation of the C-terminal residue to be active.
(10) Burkholderia cepacia, which is an unusual opportunistic pathogen that threatens immunocompromised patients, was resistant to all the peptides when they were tested individually, even at the highest concentrations that were evaluated. However, the combination of QnCs-BUAP with the peptides Uy234 and Uy192 displayed promising activity against Burkholderia cepacia, with MBCs of 150 μM and 300 μM, respectively. The effectiveness of peptide combinations has been reported, and different advantages of their use have been proposed, such as using lower doses, cost savings, and preventing the development of resistance. Combining the peptide QnCs-BUAP with the peptides Uy234, Uy17, and Uy192 resulted in the reduction of the MBC in almost all bacterial strains evaluated. Furthermore, a synergistic behavior was displayed in 25% of the resulting combinations, 37.5% displayed an additive effect, and only 8% showed antagonism.
(11) Some AMPs from scorpion venom have shown great potential to inhibit the growth of a broad spectrum of bacteria, including MDR clinical isolates; however, their high cytotoxicity and hemolytic activity have prevented their clinical use. According to our results, the three AMPs from U. yaschenkoi and the consensus peptide QnCs-BUAP displayed remarkably low hemolytic activity compared to that of other AMPs from scorpion venom. The hemolytic concentration (HC) of the peptides Uy17, Uy192 and Uy234 towards pig erythrocytes was previously reported with an HC25 = 26.65 μM, 35.85 μM and 55.14 μM, respectively; in our work, the same peptide sequences showed lower hemolytic activity against human erythrocytes, requiring greater peptide concentrations (> 370 μM) to achieve the same HC25.
(12) The mechanism of the antimicrobial action of these AMPs is not fully understood; however, it is generally accepted that the ability of AMPs to kill microorganisms depends upon their capacity to bind to the membranes of these microorganisms. The ability of an AMP to interact with a target membrane depends upon its structure and the membrane target; in the case of short-chain AMPs without cysteine, the α-helical structure of the AMPs is key to achieving the interaction with the membrane target, as is the higher positive charge that is provided by the amidation of the C-terminal residue. The antimicrobial peptides evaluated in this article showed strong activity against Streptococcus sp., while exerted none effect against Burkholderia cepacia, it may be due to Streptococcus sp. is a Gram-positive bacterium, so it does not have an outer cellular membrane making it a sensitive target of the action of the AMPs. On the other hand, Burkholderia cepacia is a Gram-negative bacterium, so it has a double cell membrane representing a double barrier against the action of AMPs.
(13) Furthermore, there is a relationship of bacterial membrane lipid composition and the potency of certain antimicrobial agents. Bacteria vary widely in the lipid composition (cardiolipin, phosphatidylglycerol and phosphatidylethanolamine) of their membranes and would, therefore, be expected to exhibit different sensitivities to antimicrobial compounds. This may explain why the different Gram-Positive and Gram-negative bacteria evaluated in this work have a different degree of susceptibility to the peptides tested. In general, Gram-negative bacteria show higher phosphatidylethanolamine content than Gram-positive bacteria. However, Gram-positive bacteria exhibit a higher amount of anionic lipids (phosphatidylglycerol and cardiolipin). The presence of charge in the lipids favors the electrostatic interactions with cationic AMPs, followed by insertion of peptides in the lipid bilayer and then the AMPs destabilize the membrane making it permeable or disrupting it.
(14) Finally, the synergic effect of each peptide with the QnCs-BUAP peptide may be due to the fact that each combination results in a higher positive charge, which can achieve greater interaction with the lipids of the membrane and lead to destabilize it causing its rupture. The IsCT and IsCT2 peptides from the venom of the African scorpion Opisthacanthus madagascarienis were the first peptides studied of this type of AMP. Structure-function analysis of IsCT and IsCT2 revealed a linear α-helical structure. The reduced antimicrobial activity of non-amidated AMPs is due to the decrease in the positive surface charge and the structural alteration of the α-helix, which affects the ability of the AMP to disrupt the cell membrane. Synergism assays revealed the effectiveness of the combined use of the four peptides, although the mechanism of synergism remains to be elucidated. The antimicrobial peptides evaluated in this work could be valuable tools for the design and development of effective AMPs against bacteria resistant to the currently available antibiotics.14. According to the text, what is the reason behind the reduced antimicrobial activity of non-amidated AMPs?
Correct
Answer (D) is the right answer. In paragraph 14 it is stated that “The reduced antimicrobial activity of non-amidated AMPs is due to the decrease in the positive surface charge and the structural alteration of the α-helix, which affects the ability of the AMP to disrupt the cell membrane.” So option A is wrong since the decrease in the positive surface charge is mentioned as a reason and not increase. The other options are simply not mentioned to be reasons behind the reduced antimicrobial activity of non-amidated AMPs.
Incorrect
Answer (D) is the right answer. In paragraph 14 it is stated that “The reduced antimicrobial activity of non-amidated AMPs is due to the decrease in the positive surface charge and the structural alteration of the α-helix, which affects the ability of the AMP to disrupt the cell membrane.” So option A is wrong since the decrease in the positive surface charge is mentioned as a reason and not increase. The other options are simply not mentioned to be reasons behind the reduced antimicrobial activity of non-amidated AMPs.
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Question 15 of 17
15. Question
Structural characterization of scorpion peptides and their bactericidal activity against clinical isolates of multidrug-resistant bacteria
(1) Scorpions are arthropods belonging to the group of arachnids, which have lived on our planet for more than 400 million years. Currently, approximately 1500 species of scorpions have been described, and the study of their venoms has resulted in the discovery of a large arsenal of bioactive molecules; among these molecules, toxins are distinguished by their ability to modulate the function of diverse ion channels and membrane receptors, causing the symptoms of poisoning. Other interesting biomolecules that have been discovered in scorpion venoms are antimicrobial peptides (AMPs), which stand out for their broad-spectrum activity against Gram-positive and Gram-negative bacteria, fungi, yeast, and protozoa. The most interesting AMPs from scorpion venoms are those falling out of the Buthidae family, which do not present any risk to human health; the venoms contain antimicrobial peptides (AMPs) involved in the innate immune response of venomous arthropods. Scorpion AMPs also function as internal immune agents protecting the venom gland from infection and external immune agents cleaning saprophytic microbes from the surface of the scorpion body. In addition, synergistic effects of antimicrobial scorpion peptide and neurotoxins against bacteria has been described, which provides further evidence in favor of the multifunctionality of scorpion venom components. Most of these antimicrobial peptides do not contain disulfide bridges in their structure, known as non-disulfide-bridged peptides (NDBP), and have been classified into several groups, such as scorpine-like, long, intermediate and short-chain AMPs.
(2) Scorpine-like AMPs possess two structural and functional domains: a N-terminal α-helix (with cytolytic and/or antimicrobial activity like the insect defensins) and a tightly folded C-terminal region with a CSαβ motif, displaying K+ channel-blocking activity. The first characterized scorpine was isolated from the venom of the scorpion Pandinus imperator. This protein is formed by 75 amino acids and has shown antimicrobial activity, mainly against Bacillus subtilis, although it also has an inhibitory effect on the ookinete and gamete stages of Plasmodium berghei.
(3) Long-chain AMPs, such as hadrurin (isolated from Mexican scorpion Hadrurus aztecus), belong to the superfamily of peptides without disulfide bridges. This 41-amino acid peptide forms helical structures and has antimicrobial activity against Gram-negative bacteria, such as Salmonella typhi, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Other related peptides, such as Opistoporin-1 (Opistophthalmus carinatus) and Pandinin-1 (Pandinus imperator), both with 44 amino acids, have antimicrobial activity against Gram-positive and Gram-negative bacteria, respectively.
(4) AMPs from the scorpion Heterometrus spinifer have been reported within the group of AMPs with an intermediate size peptide chain; one of these peptides is HsAp (29 amino acids), which has broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, as well as antifungal activity; however, HsAp has limited therapeutic use because it is highly hemolytic against human erythrocytes. Other peptides included in this classification are: Heterin-2 and pandinin-2. Heterin-2 is a venom peptide from the scorpion Heterometrus spinifer which contains 24 amino acid residues. Heterin-2 is able to inhibit the growth of Gram-positive bacteria with MICs from 5.6 μM to 30.0 μM. Pandinin-2 is an α-helical polycationic antimicrobial peptide from venom of the scorpion Pandinus imperator. Pandinin-2 contains 24 amino acid residues and demonstrated high antimicrobial activity against a range of Gram-positive bacteria (2.4–5.2 μM), but was less active against Gram-negative bacteria (2.4–38.2 μM).
(5) Short-chain AMPs or IsCT-type peptides are short antimicrobial peptides derived from longer peptide precursors by post-translational processing of a signal peptide and a carboxy-terminal propeptide region that flank the mature peptide. The mature peptide contains commonly less than 20 amino acids, most of them hydrophobic.
(6) Currently, 67 IsCT-type AMPs have been reported. The first IsCT peptide was isolated from the venom of the scorpion Opisthacanthus madagascariensis; it was named in this way because the scorpion was found in Isalo (Is), Madagascar and the peptide displayed cytotoxic activity (CT). IsCT peptide presents antibacterial activity against Gram-negative and Gram-positive strains of bacteria and low hemolytic activity. Other short peptides from Mexican scorpions have also been identified, e.g., VmCT1 and VmCT2 from the scorpion Vaejovis mexicanus. From the cDNA libraries made from the venom glands of this scorpion belonging to the Vaejovidae family, the sequences of these peptides were identified. The chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity as well as low hemolytic activity. The mechanism of action of these AMPs however is unclear.
(7) Recently, as a result of the transcriptomic analysis of the venomous glands of the Urodacus yaschenkoi scorpion, the existence of a large number of peptides with potential antimicrobial activity (mainly NDBP type) was discovered. The antimicrobial activity of several of these peptides (chemically synthesized) has been evaluated e.g., the UyCT3 peptide with an amidated C-terminal showed strong antimicrobial activity, while the non-amidated UyCT3 peptide failed to exhibit any antimicrobial activity, confirming the importance of the amidation of the C-terminus. The development of new technology platforms for peptide synthesis and modification with a low cost makes peptide systems valuable tools for the design of new therapeutic weapons against multidrug-resistant (MDR) strains.
(8) The rise of MDR bacteria represents a major public health problem worldwide; consequently, global research is focused on the development of new therapeutic agents. Scorpion venoms represent an immense source of bioactive peptides, including toxins that affect the sodium channels of mammals or insects and AMPs. However, only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains. Among NDBPs with antimicrobial activity, scorpion venoms contain peptides such as Opistoporin, Pandinin or IsCT types.
(9) Urodacus yaschenkoi is an Australian scorpion that has been characterized and contains an arsenal of biomolecules with diverse functions, including AMPs. Previous studies have reported that three of these peptides (UyCT1, UyCT3, and UyCT5) have been effective in inhibiting a broad spectrum of bacteria, including MDR pathogens such as Acinetobacter baumannii, and these peptides required the amidation of the C-terminal residue to be active.
(10) Burkholderia cepacia, which is an unusual opportunistic pathogen that threatens immunocompromised patients, was resistant to all the peptides when they were tested individually, even at the highest concentrations that were evaluated. However, the combination of QnCs-BUAP with the peptides Uy234 and Uy192 displayed promising activity against Burkholderia cepacia, with MBCs of 150 μM and 300 μM, respectively. The effectiveness of peptide combinations has been reported, and different advantages of their use have been proposed, such as using lower doses, cost savings, and preventing the development of resistance. Combining the peptide QnCs-BUAP with the peptides Uy234, Uy17, and Uy192 resulted in the reduction of the MBC in almost all bacterial strains evaluated. Furthermore, a synergistic behavior was displayed in 25% of the resulting combinations, 37.5% displayed an additive effect, and only 8% showed antagonism.
(11) Some AMPs from scorpion venom have shown great potential to inhibit the growth of a broad spectrum of bacteria, including MDR clinical isolates; however, their high cytotoxicity and hemolytic activity have prevented their clinical use. According to our results, the three AMPs from U. yaschenkoi and the consensus peptide QnCs-BUAP displayed remarkably low hemolytic activity compared to that of other AMPs from scorpion venom. The hemolytic concentration (HC) of the peptides Uy17, Uy192 and Uy234 towards pig erythrocytes was previously reported with an HC25 = 26.65 μM, 35.85 μM and 55.14 μM, respectively; in our work, the same peptide sequences showed lower hemolytic activity against human erythrocytes, requiring greater peptide concentrations (> 370 μM) to achieve the same HC25.
(12) The mechanism of the antimicrobial action of these AMPs is not fully understood; however, it is generally accepted that the ability of AMPs to kill microorganisms depends upon their capacity to bind to the membranes of these microorganisms. The ability of an AMP to interact with a target membrane depends upon its structure and the membrane target; in the case of short-chain AMPs without cysteine, the α-helical structure of the AMPs is key to achieving the interaction with the membrane target, as is the higher positive charge that is provided by the amidation of the C-terminal residue. The antimicrobial peptides evaluated in this article showed strong activity against Streptococcus sp., while exerted none effect against Burkholderia cepacia, it may be due to Streptococcus sp. is a Gram-positive bacterium, so it does not have an outer cellular membrane making it a sensitive target of the action of the AMPs. On the other hand, Burkholderia cepacia is a Gram-negative bacterium, so it has a double cell membrane representing a double barrier against the action of AMPs.
(13) Furthermore, there is a relationship of bacterial membrane lipid composition and the potency of certain antimicrobial agents. Bacteria vary widely in the lipid composition (cardiolipin, phosphatidylglycerol and phosphatidylethanolamine) of their membranes and would, therefore, be expected to exhibit different sensitivities to antimicrobial compounds. This may explain why the different Gram-Positive and Gram-negative bacteria evaluated in this work have a different degree of susceptibility to the peptides tested. In general, Gram-negative bacteria show higher phosphatidylethanolamine content than Gram-positive bacteria. However, Gram-positive bacteria exhibit a higher amount of anionic lipids (phosphatidylglycerol and cardiolipin). The presence of charge in the lipids favors the electrostatic interactions with cationic AMPs, followed by insertion of peptides in the lipid bilayer and then the AMPs destabilize the membrane making it permeable or disrupting it.
(14) Finally, the synergic effect of each peptide with the QnCs-BUAP peptide may be due to the fact that each combination results in a higher positive charge, which can achieve greater interaction with the lipids of the membrane and lead to destabilize it causing its rupture. The IsCT and IsCT2 peptides from the venom of the African scorpion Opisthacanthus madagascarienis were the first peptides studied of this type of AMP. Structure-function analysis of IsCT and IsCT2 revealed a linear α-helical structure. The reduced antimicrobial activity of non-amidated AMPs is due to the decrease in the positive surface charge and the structural alteration of the α-helix, which affects the ability of the AMP to disrupt the cell membrane. Synergism assays revealed the effectiveness of the combined use of the four peptides, although the mechanism of synergism remains to be elucidated. The antimicrobial peptides evaluated in this work could be valuable tools for the design and development of effective AMPs against bacteria resistant to the currently available antibiotics.15. Based on the passage we can understand that the author probably:
Correct
(B) is the correct answer, we can see in the passage that the author reports facts and findings of the researchers and supports his/her statements with those findings.
Incorrect
(B) is the correct answer, we can see in the passage that the author reports facts and findings of the researchers and supports his/her statements with those findings.
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Question 16 of 17
16. Question
Structural characterization of scorpion peptides and their bactericidal activity against clinical isolates of multidrug-resistant bacteria
(1) Scorpions are arthropods belonging to the group of arachnids, which have lived on our planet for more than 400 million years. Currently, approximately 1500 species of scorpions have been described, and the study of their venoms has resulted in the discovery of a large arsenal of bioactive molecules; among these molecules, toxins are distinguished by their ability to modulate the function of diverse ion channels and membrane receptors, causing the symptoms of poisoning. Other interesting biomolecules that have been discovered in scorpion venoms are antimicrobial peptides (AMPs), which stand out for their broad-spectrum activity against Gram-positive and Gram-negative bacteria, fungi, yeast, and protozoa. The most interesting AMPs from scorpion venoms are those falling out of the Buthidae family, which do not present any risk to human health; the venoms contain antimicrobial peptides (AMPs) involved in the innate immune response of venomous arthropods. Scorpion AMPs also function as internal immune agents protecting the venom gland from infection and external immune agents cleaning saprophytic microbes from the surface of the scorpion body. In addition, synergistic effects of antimicrobial scorpion peptide and neurotoxins against bacteria has been described, which provides further evidence in favor of the multifunctionality of scorpion venom components. Most of these antimicrobial peptides do not contain disulfide bridges in their structure, known as non-disulfide-bridged peptides (NDBP), and have been classified into several groups, such as scorpine-like, long, intermediate and short-chain AMPs.
(2) Scorpine-like AMPs possess two structural and functional domains: a N-terminal α-helix (with cytolytic and/or antimicrobial activity like the insect defensins) and a tightly folded C-terminal region with a CSαβ motif, displaying K+ channel-blocking activity. The first characterized scorpine was isolated from the venom of the scorpion Pandinus imperator. This protein is formed by 75 amino acids and has shown antimicrobial activity, mainly against Bacillus subtilis, although it also has an inhibitory effect on the ookinete and gamete stages of Plasmodium berghei.
(3) Long-chain AMPs, such as hadrurin (isolated from Mexican scorpion Hadrurus aztecus), belong to the superfamily of peptides without disulfide bridges. This 41-amino acid peptide forms helical structures and has antimicrobial activity against Gram-negative bacteria, such as Salmonella typhi, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Other related peptides, such as Opistoporin-1 (Opistophthalmus carinatus) and Pandinin-1 (Pandinus imperator), both with 44 amino acids, have antimicrobial activity against Gram-positive and Gram-negative bacteria, respectively.
(4) AMPs from the scorpion Heterometrus spinifer have been reported within the group of AMPs with an intermediate size peptide chain; one of these peptides is HsAp (29 amino acids), which has broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, as well as antifungal activity; however, HsAp has limited therapeutic use because it is highly hemolytic against human erythrocytes. Other peptides included in this classification are: Heterin-2 and pandinin-2. Heterin-2 is a venom peptide from the scorpion Heterometrus spinifer which contains 24 amino acid residues. Heterin-2 is able to inhibit the growth of Gram-positive bacteria with MICs from 5.6 μM to 30.0 μM. Pandinin-2 is an α-helical polycationic antimicrobial peptide from venom of the scorpion Pandinus imperator. Pandinin-2 contains 24 amino acid residues and demonstrated high antimicrobial activity against a range of Gram-positive bacteria (2.4–5.2 μM), but was less active against Gram-negative bacteria (2.4–38.2 μM).
(5) Short-chain AMPs or IsCT-type peptides are short antimicrobial peptides derived from longer peptide precursors by post-translational processing of a signal peptide and a carboxy-terminal propeptide region that flank the mature peptide. The mature peptide contains commonly less than 20 amino acids, most of them hydrophobic.
(6) Currently, 67 IsCT-type AMPs have been reported. The first IsCT peptide was isolated from the venom of the scorpion Opisthacanthus madagascariensis; it was named in this way because the scorpion was found in Isalo (Is), Madagascar and the peptide displayed cytotoxic activity (CT). IsCT peptide presents antibacterial activity against Gram-negative and Gram-positive strains of bacteria and low hemolytic activity. Other short peptides from Mexican scorpions have also been identified, e.g., VmCT1 and VmCT2 from the scorpion Vaejovis mexicanus. From the cDNA libraries made from the venom glands of this scorpion belonging to the Vaejovidae family, the sequences of these peptides were identified. The chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity as well as low hemolytic activity. The mechanism of action of these AMPs however is unclear.
(7) Recently, as a result of the transcriptomic analysis of the venomous glands of the Urodacus yaschenkoi scorpion, the existence of a large number of peptides with potential antimicrobial activity (mainly NDBP type) was discovered. The antimicrobial activity of several of these peptides (chemically synthesized) has been evaluated e.g., the UyCT3 peptide with an amidated C-terminal showed strong antimicrobial activity, while the non-amidated UyCT3 peptide failed to exhibit any antimicrobial activity, confirming the importance of the amidation of the C-terminus. The development of new technology platforms for peptide synthesis and modification with a low cost makes peptide systems valuable tools for the design of new therapeutic weapons against multidrug-resistant (MDR) strains.
(8) The rise of MDR bacteria represents a major public health problem worldwide; consequently, global research is focused on the development of new therapeutic agents. Scorpion venoms represent an immense source of bioactive peptides, including toxins that affect the sodium channels of mammals or insects and AMPs. However, only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains. Among NDBPs with antimicrobial activity, scorpion venoms contain peptides such as Opistoporin, Pandinin or IsCT types.
(9) Urodacus yaschenkoi is an Australian scorpion that has been characterized and contains an arsenal of biomolecules with diverse functions, including AMPs. Previous studies have reported that three of these peptides (UyCT1, UyCT3, and UyCT5) have been effective in inhibiting a broad spectrum of bacteria, including MDR pathogens such as Acinetobacter baumannii, and these peptides required the amidation of the C-terminal residue to be active.
(10) Burkholderia cepacia, which is an unusual opportunistic pathogen that threatens immunocompromised patients, was resistant to all the peptides when they were tested individually, even at the highest concentrations that were evaluated. However, the combination of QnCs-BUAP with the peptides Uy234 and Uy192 displayed promising activity against Burkholderia cepacia, with MBCs of 150 μM and 300 μM, respectively. The effectiveness of peptide combinations has been reported, and different advantages of their use have been proposed, such as using lower doses, cost savings, and preventing the development of resistance. Combining the peptide QnCs-BUAP with the peptides Uy234, Uy17, and Uy192 resulted in the reduction of the MBC in almost all bacterial strains evaluated. Furthermore, a synergistic behavior was displayed in 25% of the resulting combinations, 37.5% displayed an additive effect, and only 8% showed antagonism.
(11) Some AMPs from scorpion venom have shown great potential to inhibit the growth of a broad spectrum of bacteria, including MDR clinical isolates; however, their high cytotoxicity and hemolytic activity have prevented their clinical use. According to our results, the three AMPs from U. yaschenkoi and the consensus peptide QnCs-BUAP displayed remarkably low hemolytic activity compared to that of other AMPs from scorpion venom. The hemolytic concentration (HC) of the peptides Uy17, Uy192 and Uy234 towards pig erythrocytes was previously reported with an HC25 = 26.65 μM, 35.85 μM and 55.14 μM, respectively; in our work, the same peptide sequences showed lower hemolytic activity against human erythrocytes, requiring greater peptide concentrations (> 370 μM) to achieve the same HC25.
(12) The mechanism of the antimicrobial action of these AMPs is not fully understood; however, it is generally accepted that the ability of AMPs to kill microorganisms depends upon their capacity to bind to the membranes of these microorganisms. The ability of an AMP to interact with a target membrane depends upon its structure and the membrane target; in the case of short-chain AMPs without cysteine, the α-helical structure of the AMPs is key to achieving the interaction with the membrane target, as is the higher positive charge that is provided by the amidation of the C-terminal residue. The antimicrobial peptides evaluated in this article showed strong activity against Streptococcus sp., while exerted none effect against Burkholderia cepacia, it may be due to Streptococcus sp. is a Gram-positive bacterium, so it does not have an outer cellular membrane making it a sensitive target of the action of the AMPs. On the other hand, Burkholderia cepacia is a Gram-negative bacterium, so it has a double cell membrane representing a double barrier against the action of AMPs.
(13) Furthermore, there is a relationship of bacterial membrane lipid composition and the potency of certain antimicrobial agents. Bacteria vary widely in the lipid composition (cardiolipin, phosphatidylglycerol and phosphatidylethanolamine) of their membranes and would, therefore, be expected to exhibit different sensitivities to antimicrobial compounds. This may explain why the different Gram-Positive and Gram-negative bacteria evaluated in this work have a different degree of susceptibility to the peptides tested. In general, Gram-negative bacteria show higher phosphatidylethanolamine content than Gram-positive bacteria. However, Gram-positive bacteria exhibit a higher amount of anionic lipids (phosphatidylglycerol and cardiolipin). The presence of charge in the lipids favors the electrostatic interactions with cationic AMPs, followed by insertion of peptides in the lipid bilayer and then the AMPs destabilize the membrane making it permeable or disrupting it.
(14) Finally, the synergic effect of each peptide with the QnCs-BUAP peptide may be due to the fact that each combination results in a higher positive charge, which can achieve greater interaction with the lipids of the membrane and lead to destabilize it causing its rupture. The IsCT and IsCT2 peptides from the venom of the African scorpion Opisthacanthus madagascarienis were the first peptides studied of this type of AMP. Structure-function analysis of IsCT and IsCT2 revealed a linear α-helical structure. The reduced antimicrobial activity of non-amidated AMPs is due to the decrease in the positive surface charge and the structural alteration of the α-helix, which affects the ability of the AMP to disrupt the cell membrane. Synergism assays revealed the effectiveness of the combined use of the four peptides, although the mechanism of synergism remains to be elucidated. The antimicrobial peptides evaluated in this work could be valuable tools for the design and development of effective AMPs against bacteria resistant to the currently available antibiotics.16. Which of the following best describes the foundation of the author’s argument in the passage?
Correct
(C) is the correct choice, the author provides tests and their results conducted by scientists and also provides data and his arguments are based on these. So we can conclude that his/her arguments are based on scientific evidence and are objective. Objective arguments are often those that have to do with logos, that is, reason, evidence, and logic, generally dealing with material questions (things that can be sensed or measured and have to do with the real outside world, outside of oneself).
Incorrect
(C) is the correct choice, the author provides tests and their results conducted by scientists and also provides data and his arguments are based on these. So we can conclude that his/her arguments are based on scientific evidence and are objective. Objective arguments are often those that have to do with logos, that is, reason, evidence, and logic, generally dealing with material questions (things that can be sensed or measured and have to do with the real outside world, outside of oneself).
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Question 17 of 17
17. Question
Structural characterization of scorpion peptides and their bactericidal activity against clinical isolates of multidrug-resistant bacteria
(1) Scorpions are arthropods belonging to the group of arachnids, which have lived on our planet for more than 400 million years. Currently, approximately 1500 species of scorpions have been described, and the study of their venoms has resulted in the discovery of a large arsenal of bioactive molecules; among these molecules, toxins are distinguished by their ability to modulate the function of diverse ion channels and membrane receptors, causing the symptoms of poisoning. Other interesting biomolecules that have been discovered in scorpion venoms are antimicrobial peptides (AMPs), which stand out for their broad-spectrum activity against Gram-positive and Gram-negative bacteria, fungi, yeast, and protozoa. The most interesting AMPs from scorpion venoms are those falling out of the Buthidae family, which do not present any risk to human health; the venoms contain antimicrobial peptides (AMPs) involved in the innate immune response of venomous arthropods. Scorpion AMPs also function as internal immune agents protecting the venom gland from infection and external immune agents cleaning saprophytic microbes from the surface of the scorpion body. In addition, synergistic effects of antimicrobial scorpion peptide and neurotoxins against bacteria has been described, which provides further evidence in favor of the multifunctionality of scorpion venom components. Most of these antimicrobial peptides do not contain disulfide bridges in their structure, known as non-disulfide-bridged peptides (NDBP), and have been classified into several groups, such as scorpine-like, long, intermediate and short-chain AMPs.
(2) Scorpine-like AMPs possess two structural and functional domains: a N-terminal α-helix (with cytolytic and/or antimicrobial activity like the insect defensins) and a tightly folded C-terminal region with a CSαβ motif, displaying K+ channel-blocking activity. The first characterized scorpine was isolated from the venom of the scorpion Pandinus imperator. This protein is formed by 75 amino acids and has shown antimicrobial activity, mainly against Bacillus subtilis, although it also has an inhibitory effect on the ookinete and gamete stages of Plasmodium berghei.
(3) Long-chain AMPs, such as hadrurin (isolated from Mexican scorpion Hadrurus aztecus), belong to the superfamily of peptides without disulfide bridges. This 41-amino acid peptide forms helical structures and has antimicrobial activity against Gram-negative bacteria, such as Salmonella typhi, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Other related peptides, such as Opistoporin-1 (Opistophthalmus carinatus) and Pandinin-1 (Pandinus imperator), both with 44 amino acids, have antimicrobial activity against Gram-positive and Gram-negative bacteria, respectively.
(4) AMPs from the scorpion Heterometrus spinifer have been reported within the group of AMPs with an intermediate size peptide chain; one of these peptides is HsAp (29 amino acids), which has broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria, as well as antifungal activity; however, HsAp has limited therapeutic use because it is highly hemolytic against human erythrocytes. Other peptides included in this classification are: Heterin-2 and pandinin-2. Heterin-2 is a venom peptide from the scorpion Heterometrus spinifer which contains 24 amino acid residues. Heterin-2 is able to inhibit the growth of Gram-positive bacteria with MICs from 5.6 μM to 30.0 μM. Pandinin-2 is an α-helical polycationic antimicrobial peptide from venom of the scorpion Pandinus imperator. Pandinin-2 contains 24 amino acid residues and demonstrated high antimicrobial activity against a range of Gram-positive bacteria (2.4–5.2 μM), but was less active against Gram-negative bacteria (2.4–38.2 μM).
(5) Short-chain AMPs or IsCT-type peptides are short antimicrobial peptides derived from longer peptide precursors by post-translational processing of a signal peptide and a carboxy-terminal propeptide region that flank the mature peptide. The mature peptide contains commonly less than 20 amino acids, most of them hydrophobic.
(6) Currently, 67 IsCT-type AMPs have been reported. The first IsCT peptide was isolated from the venom of the scorpion Opisthacanthus madagascariensis; it was named in this way because the scorpion was found in Isalo (Is), Madagascar and the peptide displayed cytotoxic activity (CT). IsCT peptide presents antibacterial activity against Gram-negative and Gram-positive strains of bacteria and low hemolytic activity. Other short peptides from Mexican scorpions have also been identified, e.g., VmCT1 and VmCT2 from the scorpion Vaejovis mexicanus. From the cDNA libraries made from the venom glands of this scorpion belonging to the Vaejovidae family, the sequences of these peptides were identified. The chemically synthesized peptides (with C-terminal amidation) showed potent antibacterial activity as well as low hemolytic activity. The mechanism of action of these AMPs however is unclear.
(7) Recently, as a result of the transcriptomic analysis of the venomous glands of the Urodacus yaschenkoi scorpion, the existence of a large number of peptides with potential antimicrobial activity (mainly NDBP type) was discovered. The antimicrobial activity of several of these peptides (chemically synthesized) has been evaluated e.g., the UyCT3 peptide with an amidated C-terminal showed strong antimicrobial activity, while the non-amidated UyCT3 peptide failed to exhibit any antimicrobial activity, confirming the importance of the amidation of the C-terminus. The development of new technology platforms for peptide synthesis and modification with a low cost makes peptide systems valuable tools for the design of new therapeutic weapons against multidrug-resistant (MDR) strains.
(8) The rise of MDR bacteria represents a major public health problem worldwide; consequently, global research is focused on the development of new therapeutic agents. Scorpion venoms represent an immense source of bioactive peptides, including toxins that affect the sodium channels of mammals or insects and AMPs. However, only a few scorpion peptides with antimicrobial activity have been characterized and evaluated against MDR bacterial strains. Among NDBPs with antimicrobial activity, scorpion venoms contain peptides such as Opistoporin, Pandinin or IsCT types.
(9) Urodacus yaschenkoi is an Australian scorpion that has been characterized and contains an arsenal of biomolecules with diverse functions, including AMPs. Previous studies have reported that three of these peptides (UyCT1, UyCT3, and UyCT5) have been effective in inhibiting a broad spectrum of bacteria, including MDR pathogens such as Acinetobacter baumannii, and these peptides required the amidation of the C-terminal residue to be active.
(10) Burkholderia cepacia, which is an unusual opportunistic pathogen that threatens immunocompromised patients, was resistant to all the peptides when they were tested individually, even at the highest concentrations that were evaluated. However, the combination of QnCs-BUAP with the peptides Uy234 and Uy192 displayed promising activity against Burkholderia cepacia, with MBCs of 150 μM and 300 μM, respectively. The effectiveness of peptide combinations has been reported, and different advantages of their use have been proposed, such as using lower doses, cost savings, and preventing the development of resistance. Combining the peptide QnCs-BUAP with the peptides Uy234, Uy17, and Uy192 resulted in the reduction of the MBC in almost all bacterial strains evaluated. Furthermore, a synergistic behavior was displayed in 25% of the resulting combinations, 37.5% displayed an additive effect, and only 8% showed antagonism.
(11) Some AMPs from scorpion venom have shown great potential to inhibit the growth of a broad spectrum of bacteria, including MDR clinical isolates; however, their high cytotoxicity and hemolytic activity have prevented their clinical use. According to our results, the three AMPs from U. yaschenkoi and the consensus peptide QnCs-BUAP displayed remarkably low hemolytic activity compared to that of other AMPs from scorpion venom. The hemolytic concentration (HC) of the peptides Uy17, Uy192 and Uy234 towards pig erythrocytes was previously reported with an HC25 = 26.65 μM, 35.85 μM and 55.14 μM, respectively; in our work, the same peptide sequences showed lower hemolytic activity against human erythrocytes, requiring greater peptide concentrations (> 370 μM) to achieve the same HC25.
(12) The mechanism of the antimicrobial action of these AMPs is not fully understood; however, it is generally accepted that the ability of AMPs to kill microorganisms depends upon their capacity to bind to the membranes of these microorganisms. The ability of an AMP to interact with a target membrane depends upon its structure and the membrane target; in the case of short-chain AMPs without cysteine, the α-helical structure of the AMPs is key to achieving the interaction with the membrane target, as is the higher positive charge that is provided by the amidation of the C-terminal residue. The antimicrobial peptides evaluated in this article showed strong activity against Streptococcus sp., while exerted none effect against Burkholderia cepacia, it may be due to Streptococcus sp. is a Gram-positive bacterium, so it does not have an outer cellular membrane making it a sensitive target of the action of the AMPs. On the other hand, Burkholderia cepacia is a Gram-negative bacterium, so it has a double cell membrane representing a double barrier against the action of AMPs.
(13) Furthermore, there is a relationship of bacterial membrane lipid composition and the potency of certain antimicrobial agents. Bacteria vary widely in the lipid composition (cardiolipin, phosphatidylglycerol and phosphatidylethanolamine) of their membranes and would, therefore, be expected to exhibit different sensitivities to antimicrobial compounds. This may explain why the different Gram-Positive and Gram-negative bacteria evaluated in this work have a different degree of susceptibility to the peptides tested. In general, Gram-negative bacteria show higher phosphatidylethanolamine content than Gram-positive bacteria. However, Gram-positive bacteria exhibit a higher amount of anionic lipids (phosphatidylglycerol and cardiolipin). The presence of charge in the lipids favors the electrostatic interactions with cationic AMPs, followed by insertion of peptides in the lipid bilayer and then the AMPs destabilize the membrane making it permeable or disrupting it.
(14) Finally, the synergic effect of each peptide with the QnCs-BUAP peptide may be due to the fact that each combination results in a higher positive charge, which can achieve greater interaction with the lipids of the membrane and lead to destabilize it causing its rupture. The IsCT and IsCT2 peptides from the venom of the African scorpion Opisthacanthus madagascarienis were the first peptides studied of this type of AMP. Structure-function analysis of IsCT and IsCT2 revealed a linear α-helical structure. The reduced antimicrobial activity of non-amidated AMPs is due to the decrease in the positive surface charge and the structural alteration of the α-helix, which affects the ability of the AMP to disrupt the cell membrane. Synergism assays revealed the effectiveness of the combined use of the four peptides, although the mechanism of synergism remains to be elucidated. The antimicrobial peptides evaluated in this work could be valuable tools for the design and development of effective AMPs against bacteria resistant to the currently available antibiotics.17. Which item is the best title for this passage?
Correct
Answer (D) is the best choice as the title of the passage. Notice that in such questions you should be always looking for an option that is the most conclusive and covers the most important topics or questions that were raised and addressed in the passage. With that in mind, option D here is our best choice, other options just refer to topics that were only discussed in some parts of the texts or are not conclusive.
Incorrect
Answer (D) is the best choice as the title of the passage. Notice that in such questions you should be always looking for an option that is the most conclusive and covers the most important topics or questions that were raised and addressed in the passage. With that in mind, option D here is our best choice, other options just refer to topics that were only discussed in some parts of the texts or are not conclusive.