Hp1404, a new antimicrobial peptide from the scorpion Heterometrus petersii

Improved N-phenylpyrrolamide inhibitors of DNA gyrase as antibacterial agents for high-priority bacterial strains

In this work, we describe an improved series of N-phenylpyrrolamide inhibitors that exhibit potent activity against DNA gyrase and are highly effective against high-priority gram-positive bacteria. The most potent compounds show low nanomolar IC50 values against Escherichia coli DNA gyrase, and in addition, compound 7c also inhibits E. coli topoisomerase IV in the nanomolar concentration range, making it a promising candidate for the development of potent dual inhibitors for these enzymes. All tested compounds show high selectivity towards the human isoform DNA topoisomerase IIα. Compounds 6a, 6d, 6e and 6f show MIC values between 0.031 and 0.0625 μg/mL against vancomycin-intermediate S. aureus (VISA) and Enterococcus faecalis strains. Compound 6g shows an inhibitory effect against the methicillin-resistant S. aureus strain (MRSA) with a MIC of 0.0625 μg/mL and against the E. faecalis strain with a MIC of 0.125 μg/mL. In a time-kill assay, compound 6d showed a dose-dependent bactericidal effect on the MRSA strain and achieved bactericidal activity at 8 × MIC after 8 h. The duration of the post-antibiotic effect (PAE) on the MRSA strain for compound 6d was 2 h, which corresponds to the PAE duration for ciprofloxacin. The compounds were not cytotoxic at effective concentrations, as determined in an MTS assay on the MCF-7 breast cancer cell line.

Antimicrobial Potential of Scorpion-Venom-Derived Peptides

The frequent and irrational use of antibiotics by humans has led to the escalating rise of antimicrobial resistance (AMR) with a high rate of morbidity-mortality worldwide, which poses a challenge to the development of effective treatments. A large number of host defense peptides from different organisms have gained interest due to their broad antibacterial spectrum, rapid action, and low target resistance, implying that these natural sources might be a new alternative to antimicrobial drugs. As important effectors of prey capture, defense against other animal attacks, and competitor deterrence, scorpion venoms have been developed as important candidate sources for modern drug development. With the rapid progress of bioanalytical and high throughput sequencing techniques, more and more scorpion-venom-derived peptides, including disulfide-bridged peptides (DBPs) and non-disulfide-bridged peptides (NDBPs), have been recently identified as having massive pharmacological activities in channelopathies, pathogen infections, and cancer treatments. In this review, we summarize the molecular diversity and corresponding structural classification of scorpion venom peptides with antibacterial, antifungal, and/or antiparasitic activity. We also aim to improve the understanding of the underlying mechanisms by which scorpion-venom-derived peptides exert these antimicrobial functions, and finally highlight their key aspects and prospects for antimicrobial therapeutic or pharmaceutical application.

A Critical Review of Short Antimicrobial Peptides from Scorpion Venoms, Their Physicochemical Attributes, and Potential for the Development of New Drugs

Scorpion venoms have proven to be excellent sources of antimicrobial agents. However, although many of them have been functionally characterized, they remain underutilized as pharmacological agents, despite their evident therapeutic potential. In this review, we discuss the physicochemical properties of short scorpion venom antimicrobial peptides (ssAMPs). Being generally short (13-25 aa) and amidated, their proven antimicrobial activity is generally explained by parameters such as their net charge, the hydrophobic moment, or the degree of helicity. However, for a complete understanding of their biological activities, also considering the properties of the target membranes is of great relevance. Here, with an extensive analysis of the physicochemical, structural, and thermodynamic parameters associated with these biomolecules, we propose a theoretical framework for the rational design of new antimicrobial drugs. Through a comparison of these physicochemical properties with the bioactivity of ssAMPs in pathogenic bacteria such as Staphylococcus aureus or Acinetobacter baumannii, it is evident that in addition to the net charge, the hydrophobic moment, electrostatic energy, or intrinsic flexibility are determining parameters to understand their performance. Although the correlation between these parameters is very complex, the consensus of our analysis suggests that there is a delicate balance between them and that modifying one affects the rest. Understanding the contribution of lipid composition to their bioactivities is also underestimated, which suggests that for each peptide, there is a physiological context to consider for the rational design of new drugs.

Anti-Staphylococcus aureus effects of natural antimicrobial peptides and the underlying mechanisms

Staphylococcus aureus can cause localized infections such as abscesses and pneumonia, as well as systemic infections such as bacteremia and sepsis. Especially, methicillin-resistant S. aureus often presents multidrug resistance, which becomes a major clinical challenge. One of the most common reasons for methicillin-resistant S. aureus antibiotic resistance is the presence of biofilms. Natural antimicrobial peptides derived from different species have shown effectiveness in combating S. aureus biofilms. In this review, we summarize the inhibitory activity of antimicrobial peptides against S. aureus planktonic cells and biofilms. We also summarize the possible inhibitory mechanisms, involving cell adhesion inhibition, membrane fracture, biofilm disruption and DNA disruption. We believe this can provide the basis for further research against S. aureus biofilm-associated infections.

Complementary Activities of Host Defence Peptides and Antibiotics in Combating Antimicrobial Resistant Bacteria

Due to their ability to eliminate antimicrobial resistant (AMR) bacteria and to modulate the immune response, host defence peptides (HDPs) hold great promise for the clinical treatment of bacterial infections. Whereas monotherapy with HDPs is not likely to become an effective first-line treatment, combinations of such peptides with antibiotics can potentially provide a path to future therapies for AMR infections. Therefore, we critically reviewed the recent literature regarding the antibacterial activity of combinations of HDPs and antibiotics against AMR bacteria and the approaches taken in these studies. Of the 86 studies compiled, 56 featured a formal assessment of synergy between agents. Of the combinations assessed, synergistic and additive interactions between HDPs and antibiotics amounted to 84.9% of the records, while indifferent and antagonistic interactions accounted for 15.1%. Penicillin, aminoglycoside, fluoro/quinolone, and glycopeptide antibiotic classes were the most frequently documented as interacting with HDPs, and Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Enterococcus faecium were the most reported bacterial species. Few studies formally evaluated the effects of combinations of HDPs and antibiotics on bacteria, and even fewer assessed such combinations against bacteria within biofilms, in animal models, or in advanced tissue infection models. Despite the biases of the current literature, the studies suggest that effective combinations of HDPs and antibiotics hold promise for the future treatment of infections caused by AMR bacteria.

Peptides with Diverse Functions from Scorpion Venom: A Great Opportunity for the Treatment of a Wide Variety of Diseases

Toxicology Research Center, Medical Basic Sciences Research Institute, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran

The venom glands are a rich source of biologically important peptides with pharmaceutical properties. Scorpion venoms have been identified as a reservoir for components that might be considered as great candidates for drug development. Pharmacological properties of the venom compounds have been confirmed in the treatment of different disorders. Ion channel blockers and AMPs are the main groups of scorpion venom components. Despite the existence of several studies about scorpion peptides, there are still valuable components to be discovered. Additionally, owing to the improvement of proteomics and transcriptomics, the number of peptide drugs is steadily increasing, which reflects the importance of these medications. This review evaluates available literatures on some important scorpion venom peptides with pharmaceutical activities. Given that the last three years have been dominated by the COVID-19 from the medical/pharmaceutical perspective, scorpion compounds with the potential against the coronavirus 2 (SARS-CoV-2) are discussed in this review.

Animal venoms: a novel source of anti-Toxoplasma gondii drug candidates

Toxoplasma gondii (T. gondii) is a nucleated intracellular parasitic protozoan with a broad host selectivity. It causes toxoplasmosis in immunocompromised or immunodeficient patients. The currently available treatments for toxoplasmosis have significant side effects as well as certain limitations, and the development of vaccines remains to be explored. Animal venoms are considered to be an important source of novel antimicrobial agents. Some peptides from animal venoms have amphipathic alpha-helix structures. They inhibit the growth of pathogens by targeting membranes to produce lethal pores and cause membrane rupture. Venom molecules generally possess immunomodulatory properties and play key roles in the suppression of pathogenic organisms. Here, we summarized literatures of the last 15 years on the interaction of animal venom peptides with T. gondii and attempt to explore the mechanisms of their interaction with parasites that involve membrane and organelle damage, immune response regulation and ion homeostasis. Finally, we analyzed some limitations of venom peptides for drug therapy and some insights into their development in future studies. It is hoped that more research will be stimulated to turn attention to the medical value of animal venoms in toxoplasmosis.

Antimicrobial Activity Developed by Scorpion Venoms and Its Peptide Component

Microbial infections represent a problem of great importance at the public health level, with a high rate of morbidity-mortality worldwide. However, treating the different diseases generated by microorganisms requires a gradual increase in acquired resistance when applying or using them against various antibiotic therapies. Resistance is caused by various molecular mechanisms of microorganisms, thus reducing their effectiveness. Consequently, there is a need to search for new opportunities through natural sources with antimicrobial activity. One alternative is using peptides present in different scorpion venoms, specifically from the Buthidae family. Different peptides with biological activity in microorganisms have been characterized as preventing their growth or inhibiting their replication. Therefore, they represent an alternative to be used in the design and development of new-generation antimicrobial drugs in different types of microorganisms, such as bacteria, fungi, viruses, and parasites. Essential aspects for its disclosure, as shown in this review, are the studies carried out on different types of peptides in scorpion venoms with activity against pathogenic microorganisms, highlighting their high therapeutic potential.

In vitro and in vivo Activity of Phibilin Against Candida albicans

The increase in the occurrence of antifungal-resistant Candida albicans infections necessitates more research to explore alternative effective and safe agents against this fungus. In this work, Phibilin, a new antimicrobial peptide obtained from Philomycus bilineatus and used in traditional Chinese medicine, effectively inhibits the growth and activities of C. albicans, including the clinical resistant strains. Phibilin is a fungicidal antimicrobial peptide that exhibited its antimicrobial effect against C. albicans mainly by disrupting the membrane and interacting with the DNA of the fungi. In particular, Phibilin induces the necrosis of C. albicans via the ROS-related pathway. Moreover, this antifungal compound inhibited the biofilm formation of C. albicans by preventing the development of hyphae in a dose-dependent manner. Furthermore, Phibilin and clotrimazole displayed a synergistic effect in inhibiting the growth of the fungi. In the mouse cutaneous infection model, Phibilin significantly inhibited the formation of skin abscesses and decreased the counts of C. albicans cells in the infected area. Overall, Phibilin is potentially an effective agent against skin infections caused by C. albicans.

Antimicrobial Peptide Analogs From Scorpions: Modifications and Structure-Activity

The rapid development of multidrug-resistant pathogens against conventional antibiotics is a global public health problem. The irrational use of antibiotics has promoted therapeutic limitations against different infections, making research of new molecules that can be applied to treat infections necessary. Antimicrobial peptides (AMPs) are a class of promising antibiotic molecules as they present broad action spectrum, potent activity, and do not easily induce resistance. Several AMPs from scorpion venoms have been described as a potential source for the development of new drugs; however, some limitations to their application are also observed. Here, we describe strategies used in several approaches to optimize scorpion AMPs, addressing their primary sequence, biotechnological potential, and characteristics that should be considered when developing an AMP derived from scorpion venoms. In addition, this review may contribute towards improving the understanding of rationally designing new molecules, targeting functional AMPs that may have a therapeutic application.

Comparative Antimicrobial Activity of Hp404 Peptide and Its Analogs against Acinetobacter baumannii

An amphipathic α-helical peptide, Hp1404, was isolated from the venomous gland of the scorpion Heterometrus petersii. Hp1404 exhibits antimicrobial activity against methicillin-resistant Staphylococcus aureus but is cytotoxic. In this study, we designed antimicrobial peptides by substituting amino acids at the 14 C-terminal residues of Hp1404 to reduce toxicity and improve antibacterial activity. The analog peptides, which had an amphipathic α-helical structure, were active against gram-positive and gram-negative bacteria, particularly multidrug-resistant Acinetobacter baumannii, and showed lower cytotoxicity than Hp1404. N-phenyl-1-naphthylamine uptake and DisC₃-5 assays demonstrated that the peptides kill bacteria by effectively permeating the outer and cytoplasmic membranes. Additionally, the analog peptides inhibited biofilm formation largely than Hp1404 at low concentrations. These results suggest that the analog peptides of Hp1404 can be used as therapeutic agents against A. baumannii infection.

Combining genetic algorithm with machine learning strategies for designing potent antimicrobial peptides

BACKGROUND

Current methods in machine learning provide approaches for solving challenging, multiple constraint design problems. While deep learning and related neural networking methods have state-of-the-art performance, their vulnerability in decision making processes leading to irrational outcomes is a major concern for their implementation. With the rising antibiotic resistance, antimicrobial peptides (AMPs) have increasingly gained attention as novel therapeutic agents. This challenging design problem requires peptides which meet the multiple constraints of limiting drug-resistance in bacteria, preventing secondary infections from imbalanced microbial flora, and avoiding immune system suppression. AMPs offer a promising, bioinspired design space to targeting antimicrobial activity, but their versatility also requires the curated selection from a combinatorial sequence space. This space is too large for brute-force methods or currently known rational design approaches outside of machine learning. While there has been progress in using the design space to more effectively target AMP activity, a widely applicable approach has been elusive. The lack of transparency in machine learning has limited the advancement of scientific knowledge of how AMPs are related among each other, and the lack of general applicability for fully rational approaches has limited a broader understanding of the design space.

METHODS

Here we combined an evolutionary method with rough set theory, a transparent machine learning approach, for designing antimicrobial peptides (AMPs). Our method achieves the customization of AMPs using supervised learning boundaries. Our system employs in vitro bacterial assays to measure fitness, codon-representation of peptides to gain flexibility of sequence selection in DNA-space with a genetic algorithm and machine learning to further accelerate the process.

RESULTS

We use supervised machine learning and a genetic algorithm to find a peptide active against S. epidermidis, a common bacterial strain for implant infections, with an improved aggregation propensity average for an improved ease of synthesis.

CONCLUSIONS

Our results demonstrate that AMP design can be customized to maintain activity and simplify production. To our knowledge, this is the first time when codon-based genetic algorithms combined with rough set theory methods is used for computational search on peptide sequences.

Antibacterial activity of a scorpion-derived peptide and its derivatives in vitro and in vivo

Antimicrobial peptides have recently become extremely popular as a novel class of antimicrobial agents. AMP MK049518 (FLGLLGSVLGSVLPSIFK), identified from the crab-scorpion Didymocentrus krausi, only possesses significant antibacterial activity against Gram-positive bacteria. In this study, a derivative G2K-S3K was designed with an excellent antibacterial spectrum and significantly higher antibacterial activity compared to the natural peptide. G2K-S3K also demonstrated excellent serum- and thermal-stability and did not induce bacterial resistance. In the Staphylococcus aureus and Pseudomonas aeruginosa -induced skin infection in mice, G2K-S3K significantly decreased bacterial counts in the wound by topical application. Thus, G2K-S3K could be a potent topical anti-infective agent against the skin infection caused by S. aureus and P. aeruginosa.

Structural characterization of scorpion peptides and their bactericidal activity against clinical isolates of multidrug-resistant bacteria

Scorpion venom peptides represent a novel source of antimicrobial peptides (AMPs) with broad-spectrum activity. In this study, we determined the minimum bactericidal concentration (MBC) of three scorpion AMPs, Uy234, Uy17, and Uy192, which are found in the venomous glands of the Urodacus yaschenkoi scorpion, against the clinical isolates of multidrug-resistant (MDR) bacteria. In addition, we tested the activity of a consensus AMP designed in our laboratory based on some previously reported IsCT-type (cytotoxic linear peptide) AMPs with the aim of obtaining higher antimicrobial activity. All peptides tested showed high antimicrobial activity against MDR clinical isolates, with the highest activity against β-hemolytic Streptococcus strains. The hemolytic activity was determined against human red blood cells and was significantly lower than that of previously reported AMPs. The α-helical structure of the four AMPs was confirmed by circular dichroism (CD). These results suggest that the four peptides can be valuable tools for the design and development of AMPs for use in the inhibition of MDR pathogenic bacteria. A clear index of synergism and additivity was found for the combination of QnCs-BUAP + Uy234, which makes these peptides the most promising candidates against pathogenic bacteria.

A scorpion venom peptide Ev37 restricts viral late entry by alkalizing acidic organelles

Viral infections still threaten human health all over the world, and many people die from viral diseases every year. However, there are no effective vaccines or drugs for preventing or managing most viral diseases. Thus, the discovery and development of broad-spectrum antiviral agents remain urgent. Here, we expressed and purified a venom peptide, Ev37, from the scorpion Euscorpiops validus in a prokaryotic system. We found that rEv37 can inhibit dengue virus type 2 (DENV-2), hepatitis C virus (HCV), Zika virus (ZIKV), and herpes simplex virus type 1 (HSV-1) infections in a dose-dependent manner at noncytotoxic concentrations, but that it has no effect on Sendai virus (SeV) and adenovirus (AdV) infections in vitro Furthermore, rEv37 alkalized acidic organelles to prevent low pH-dependent fusion of the viral membrane-endosomal membrane, which mainly blocks the release of the viral genome from the endosome to the cytoplasm and then restricts viral late entry. Taken together, our results indicate that the scorpion venom peptide Ev37 is a broad-spectrum antiviral agent with a specific molecular mechanism against viruses undergoing low pH-dependent fusion activation during entry into host cells. We conclude that Ev37 is a potential candidate for development as an antiviral drug.

Microbial production of toxins from the scorpion venom: properties and applications

Scorpion venom are composed mainly of bioactive proteins and peptides that may serve as lead compounds for the design of biotechnological tools and therapeutic drugs. However, exploring the therapeutic potential of scorpion venom components is mainly impaired by the low yield of purified toxins from milked venom. Therefore, production of toxin-derived peptides and proteins by heterologous expression is the strategy of choice for research groups and pharmaceutical industry to overcome this limitation. Recombinant expression in microorganisms is often the first choice, since bacteria and yeast systems combine high level of recombinant protein expression, fast cell growth and multiplication and simple media requirement. Herein, we present a comprehensive revision, which describes the scorpion venom components that were produced in their recombinant forms using microbial systems. In addition, we highlight the pros and cons of performing the heterologous expression of these compounds, regarding the particularities of each microorganism and how these processes can affect the application of these venom components. The most used microbial system in the heterologous expression of scorpion venom components is Escherichia coli (85%), and among all the recombinant venom components produced, 69% were neurotoxins. This review may light up future researchers in the choice of the best expression system to produce scorpion venom components of interest.

Analogs of the Scorpion Venom Peptide Stigmurin: Structural Assessment, Toxicity, and Increased Antimicrobial Activity

Scorpion venom is a rich source of biologically active components and various peptides with high-potential therapeutic use that have been characterized for their antimicrobial and antiproliferative activities. Stigmurin is a peptide identified from the Tityus stigmurus venom gland with high antibacterial and antiproliferative activities and low toxicity. Amino acid substitutions in peptides without a disulfide bridge sequence have been made with the aim of reducing their toxicity and increasing their biological activities. The purpose of this study was to evaluate the structural conformation and structural stability, as well as antimicrobial, antiproliferative, and hemolytic activities of two peptide analogs to Stigmurin, denominated StigA6 and StigA16. In silico analysis revealed the α-helix structure for both analog peptides, which was confirmed by circular dichroism. Data showed that the net charge and hydrophobic moment of the analog peptides were higher than those for Stigmurin, which can explain the increase in antimicrobial activity presented by them. Both analog peptides exhibited activity on cancerous cells similar to the native peptide; however, they were less toxic when tested on the normal cell line. These results reveal a potential biotechnological application of the analog peptides StigA6 and StigA16 as prototypes to new therapeutic agents.

Mechanisms driving the antibacterial and antibiofilm properties of Hp1404 and its analogue peptides against multidrug-resistant Pseudomonas aeruginosa

Hp1404, identified from the venom of the scorpion Heterometrus petersii, displays antimicrobial activity with cytotoxicity. Several synthetic peptides were designed based on the parent peptide Hp1404 to reduce cytotoxicity and improve activity (deletion of glycine and phenylalanine, substitution with leucine and lysine). The analogue peptides generated comprised 12 amino acids and displayed amphipathic α-helical structures, with higher hydrophobic moments and net positive charge than those of the Hp1404. The analogues showed less hemolytic and toxic effects toward mammalian cells than the Hp1404, especially Hp1404-T1e, which exhibited particularly potent antibacterial and antibiofilm activities against multidrug-resistant Pseudomonas aeruginosa (MRPA) strains. The analogue peptide Hp1404-T1e was more stable against salt and trypsin than the Hp1404. Hp1404's mechanism of action involves binding to lipopolysaccharide (LPS), thereby killing bacteria through membrane disruption. Hp1404-T1e kills bacteria more rapidly than Hp1404 and not only seems to bind more strongly to LPS but may also be able to enter bacterial cells and interact with their DNA. Additionally, Hp1404-T1e can effectively kill bacteria in vivo. The results of this study indicate that Hp1404-T1e not only displays antimicrobial activity, but is also functional in physiological conditions, confirming its potential use as an effective therapeutic agent against MRPA.

Histidine-rich Modification of a Scorpion-derived Peptide Improves Bioavailability and Inhibitory Activity against HSV-1

Rationale: HSV is one of the most widespread human viral pathogens. HSV-1 infects a large portion of the human population and causes severe diseases. The current clinical treatment for HSV-1 is based on nucleoside analogues, the use of which is limited due to drug resistance, side effects and poor bioavailability. AMPs have been identified as potential antiviral agents that may overcome these limitations. Therefore, we screened anti-HSV-1 peptides from a scorpion-derived AMP library and engineered one candidate into a histidine-rich peptide with significantly improved antiviral activity and development potential.

Methods: A venomous gland cDNA library was constructed from the scorpion Euscorpiops validus in the Yunnan Province of China. Six putative AMPs were characterized from this cDNA library, and the synthesized peptides were screened via plaque-forming assays to determine their virucidal potential. Time of addition experiments according to the infection progress of HSV-1 were used to identify the modes of action for peptides of interest. The histidine-rich modification was designed based on structural analysis of peptides by a helical wheel model and CD spectroscopy. Peptide cellular uptake and distribution were measured by flow cytometry and confocal microscopy, respectively.

Results: The peptide Eval418 was found to have high clearance activity in an HSV-1 plaque reduction assay. Eval418 exhibited dose-dependent and time-dependent inactivation of HSV-1 and dose-dependent inhibition of HSV-1 attachment to host cells. However, Eval418 scarcely suppressed an established HSV-1 infection due to poor cellular uptake. We further designed and modified Eval418 into four histidine-rich derivative peptides with enhanced antiviral activities and lower cytotoxicities. All of the derivative peptides suppressed established HSV-1 infections. One of these peptides, Eval418-FH5, not only had strong viral inactivation activity and enhanced attachment inhibitory activity but also had high inhibitory activity against intracellular HSV-1, which was consistent with its improved intracellular uptake and distribution as confirmed by confocal microscopy and flow cytometry.

Conclusion: We successfully identified an anti-HSV-1 peptide, Eval418, from a scorpion venom peptide library and designed a histidine-rich Eval418 derivative with significantly improved potential for further development as an anti-HSV-1 drug. This successful modification can provide a design strategy to improve the bioavailability, cellular distribution and antiviral activity of peptide agents.

Evaluation of the in vitro antimicrobial activity of selected Saudi scorpion venoms tested against multidrug-resistant micro-organisms

OBJECTIVES

Scorpion venoms are a rich source of bioactive peptides with promising clinical value that may lead to the discovery and development of new drugs. The present study was designed to evaluate the in vitro antimicrobial activities of the venoms extracted from three medically important Saudi scorpions (Androctonus crassicauda, Androctonus bicolor and Leiurus quinquestriatus).

METHODS

Antimicrobial assays were performed using a microplate growth inhibition assay against 10 multidrug-resistant (MDR) micro-organisms (4 Gram-negative bacteria, 2 Gram-positive bacteria and 4 fungi and yeasts) at concentrations ranging from 0 to 20mg/mL of each venom. Following qualitative analysis, dose-response assays were performed for bacterial and fungal killing curves using the MTT colorimetric assay.

RESULTS

Among the three tested scorpion venoms, only L. quinquestriatus venom showed significant broad-spectrum antimicrobial activity in a dose-dependent manner from 5 to 20mg/mL. Leiurus quinquestriatus venom inhibited the growth and survival of MDR Escherichia coli (55.2%), Acinetobacter baumannii (50.6%), Klebsiella pneumoniae (35.1%), Pseudomonas aeruginosa (31.3%), Staphylococcus aureus (36.4%), Enterococcus faecalis (47.6%), Candida albicans (31.2%) and Candida glabrata (39.0%), whereas no significant activity against Fusarium oxysporum and Aspergillus flavus was observed. In contrast, the venoms of A. crassicauda and A. bicolor did not show noticeable antimicrobial activity against any of the tested organisms.

CONCLUSIONS

The findings of the current study demonstrate that L. quinquestriatus venom possesses antimicrobial activity and thus can be used as a template for designing and development of novel antimicrobial drugs.

Insights into Antimicrobial Peptides from Spiders and Scorpions

The venoms of spiders and scorpions contain a variety of chemical compounds. Antimicrobial peptides (AMPs) from these organisms were first discovered in the 1990s. As of May 2015, there were 42 spider's and 63 scorpion's AMPs in the Antimicrobial Peptide Database (http://aps.unmc.edu/AP). These peptides have demonstrated broad or narrow-spectrum activities against bacteria, fungi, viruses, and parasites. In addition, they can be toxic to cancer cells, insects and erythrocytes. To provide insight into such an activity spectrum, this article discusses the discovery, classification, structure and activity relationships, bioinformatics analysis, and potential applications of spider and scorpion AMPs. Our analysis reveals that, in the case of linear peptides, spiders use both glycine-rich and helical peptide models for defense, whereas scorpions use two distinct helical peptide models with different amino acid compositions to exert the observed antimicrobial activities and hemolytic toxicity. Our structural bioinformatics study improves the knowledge in the field and can be used to design more selective peptides to combat tumors, parasites, and viruses.

Protein aggregation as an antibiotic design strategy

Taking advantage of the xenobiotic nature of bacterial infections, we tested whether the cytotoxicity of protein aggregation can be targeted to bacterial pathogens without affecting their mammalian hosts. In particular, we examined if peptides encoding aggregation-prone sequence segments of bacterial proteins can display antimicrobial activity by initiating toxic protein aggregation in bacteria, but not in mammalian cells. Unbiased in vitro screening of aggregating peptide sequences from bacterial genomes lead to the identification of several peptides that are strongly bactericidal against methicillin-resistant Staphylococcus aureus. Upon parenteral administration in vivo, the peptides cured mice from bacterial sepsis without apparent toxic side effects as judged from histological and hematological evaluation. We found that the peptides enter and accumulate in the bacterial cytosol where they cause aggregation of bacterial polypeptides. Although the precise chain of events that leads to cell death remains to be elucidated, the ability to tap into aggregation-prone sequences of bacterial proteomes to elicit antimicrobial activity represents a rich and unexplored chemical space to be mined in search of novel therapeutic strategies to fight infectious diseases.

Virocidal activity of Egyptian scorpion venoms against hepatitis C virus

BACKGROUND

Hepatitis C virus (HCV) is a major global health problem, causing chronic hepatitis, liver cirrhosis and hepatocellular carcinoma. Development of well-tolerated regimens with high cure rates and fewer side effects is still much needed. Recently, natural antimicrobial peptides (AMPs) are attracting more attention as biological compounds and can be a good template to develop therapeutic agents, including antiviral agents against a variety of viruses. Various AMPs have been characterized from the venom of different venomous animals including scorpions.

METHODS

The possible antiviral activities of crude venoms obtained from five Egyptian scorpion species (Leiurus quinquestriatus, Androctonus amoreuxi, A. australis, A. bicolor and Scorpio maurus palmatus) were evaluated by a cell culture method using Huh7.5 cells and the J6/JFH1-P47 strain of HCV. Time-of-addition experiments and inactivation of enzymatic activities of the venoms were carried out to determine the characteristics of the anti-HCV activities.

RESULTS

S. maurus palmatus and A. australis venoms showed anti-HCV activities, with 50% inhibitory concentrations (IC₅₀) being 6.3 ± 1.6 and 88.3 ± 5.8 μg/ml, respectively. S. maurus palmatus venom (30 μg/ml) impaired HCV infectivity in culture medium, but not inside the cells, through virocidal effect. The anti-HCV activity of this venom was not inhibited by a metalloprotease inhibitor or heating at 60°C. The antiviral activity was directed preferentially against HCV.

CONCLUSIONS

S. maurus palmatus venom is considered as a good natural source for characterization and development of novel anti-HCV agents targeting the entry step. To our knowledge, this is the first report describing antiviral activities of Egyptian scorpion venoms against HCV, and may open a new approach towards discovering antiviral compounds derived from scorpion venoms.