New view on crotamine, a small basic polypeptide myotoxin from South American rattlesnake venom

Venom: A Promising Avenue for Antimicrobial Therapeutics

Venom in medicine is well documented in the chronicles of ancient Greece and the Roman Empire and persisted into the Renaissance and even into the modern era. Venoms were not always associated with detrimental consequences. Since ancient times, the curative capacity of venom has been recognized, portraying venom as a metaphor for pharmacy and medicine. Venom proteins and peptides' antimicrobial potential has not undergone systematic exploration despite the huge literature on natural antimicrobials. In light of the escalating challenge of antimicrobial resistance and the diminishing effectiveness of antibiotics, there is a pressing need for innovative antimicrobials capable of effectively addressing illnesses caused by multidrug-resistant microorganisms. This review adds to our understanding of the effectiveness of different venom components against a host of pathogenic microorganisms. The aim is to illuminate the various antimicrobials present in venom and venom peptides, thereby emphasizing the unexplored medicinal potential for antimicrobial properties. We have presented a concise summary of the molecular examination of the venom peptides' functioning processes, as well as the current clinical and preclinical progress of venom antimicrobial peptides.

Effects of crotamine in human prostate cancer cell line

Our study presents the anticancer potential of crotamine from Crotalus durissus terrificus in human prostate cancer cell line DU-145. Crotamine isolation was conducted through RP-FPLC, its molecular mass analyzed by MALDI-TOF was 4881.4 kDa, and N-terminal sequencing confirmed crotamine identity. Crotamine demonstrated no toxicity and did not inhibit migration in HUVEC cells. Although no cell death occurred in DU-145 cells, crotamine inhibited their migration. Thus, crotamine presented potential to be a prototype of anticancer drug.

Snake Venom: A Promising Source of Neurotoxins Targeting Voltage-Gated Potassium Channels

The venom derived from various sources of snakes represents a vast collection of predominantly protein-based toxins that exhibit a wide range of biological actions, including but not limited to inflammation, pain, cytotoxicity, cardiotoxicity, and neurotoxicity. The venom of a particular snake species is composed of several toxins, while the venoms of around 600 venomous snake species collectively encompass a substantial reservoir of pharmacologically intriguing compounds. Despite extensive research efforts, a significant portion of snake venoms remains uncharacterized. Recent findings have demonstrated the potential application of neurotoxins derived from snake venom in selectively targeting voltage-gated potassium channels (Kv). These neurotoxins include BPTI-Kunitz polypeptides, PLA2 neurotoxins, CRISPs, SVSPs, and various others. This study provides a comprehensive analysis of the existing literature on the significance of Kv channels in various tissues, highlighting their crucial role as proteins susceptible to modulation by diverse snake venoms. These toxins have demonstrated potential as valuable pharmacological resources and research tools for investigating the structural and functional characteristics of Kv channels.

A Review of Rattlesnake Venoms

Venom components are invaluable in biomedical research owing to their specificity and potency. Many of these components exist in two genera of rattlesnakes, Crotalus and Sistrurus, with high toxicity and proteolytic activity variation. This review focuses on venom components within rattlesnakes, and offers a comparison and itemized list of factors dictating venom composition, as well as presenting their known characteristics, activities, and significant applications in biosciences. There are 64 families and subfamilies of proteins present in Crotalus and Sistrurus venom. Snake venom serine proteases (SVSP), snake venom metalloproteases (SVMP), and phospholipases A2 (PLA2) are the standard components in Crotalus and Sistrurus venom. Through this review, we highlight gaps in the knowledge of rattlesnake venom; there needs to be more information on the venom composition of three Crotalus species and one Sistrurus subspecies. We discuss the activity and importance of both major and minor components in biomedical research and drug development.

Past, Present, and Future of Naturally Occurring Antimicrobials Related to Snake Venoms

This review focuses on proteins and peptides with antimicrobial activity because these biopolymers can be useful in the fight against infectious diseases and to overcome the critical problem of microbial resistance to antibiotics. In fact, snakes show the highest diversification among reptiles, surviving in various environments; their innate immunity is similar to mammals and the response of their plasma to bacteria and fungi has been explored mainly in ecological studies. Snake venoms are a rich source of components that have a variety of biological functions. Among them are proteins like lectins, metalloproteinases, serine proteinases, L-amino acid oxidases, phospholipases type A₂, cysteine-rich secretory proteins, as well as many oligopeptides, such as waprins, cardiotoxins, cathelicidins, and β-defensins. In vitro, these biomolecules were shown to be active against bacteria, fungi, parasites, and viruses that are pathogenic to humans. Not only cathelicidins, but all other proteins and oligopeptides from snake venom have been proteolyzed to provide short antimicrobial peptides, or for use as templates for developing a variety of short unnatural sequences based on their structures. In addition to organizing and discussing an expressive amount of information, this review also describes new β-defensin sequences of Sistrurus miliarius that can lead to novel peptide-based antimicrobial agents, using a multidisciplinary approach that includes sequence phylogeny.

Biological and Medical Aspects Related to South American Rattlesnake Crotalus durissus (Linnaeus, 1758): A View from Colombia

In Colombia, South America, there is a subspecies of the South American rattlesnake Crotalus durissus, C. d. cumanensis, a snake of the Viperidae family, whose presence has been reduced due to the destruction of its habitat. It is an enigmatic snake from the group of pit vipers, venomous, with large articulated front fangs, special designs on its body, and a characteristic rattle on its tail. Unlike in Brazil, the occurrence of human envenomation by C. durisus in Colombia is very rare and contributes to less than 1% of envenomation caused by snakes. Its venom is a complex cocktail of proteins with different biological effects, which evolved with the purpose of paralyzing the prey, killing it, and starting its digestive process, as well as having defense functions. When its venom is injected into humans as the result of a bite, the victim presents with both local tissue damage and with systemic involvement, including a diverse degree of neurotoxic, myotoxic, nephrotoxic, and coagulopathic effects, among others. Its biological effects are being studied for use in human health, including the possible development of analgesic, muscle relaxant, anti-inflammatory, immunosuppressive, anti-infection, and antineoplastic drugs. Several groups of researchers in Brazil are very active in their contributions in this regard. In this work, a review is made of the most relevant biological and medical aspects related to the South American rattlesnake and of what may be of importance for a better understanding of the snake C. d. cumanensis, present in Colombia and Venezuela.

Origins, genomic structure and copy number variation of snake venom myotoxins

Crotamine, myotoxin a and homologs are short peptides that often comprise major fractions of rattlesnake venoms and have been extensively studied for their bioactive properties. These toxins are thought to be important for rapidly immobilizing mammalian prey and are implicated in serious, and sometimes fatal, responses to envenomation in humans. While high quality reference genomes for multiple venomous snakes are available, the loci that encode myotoxins have not been successfully assembled in any existing genome assembly. Here, we integrate new and existing genomic and transcriptomic data from the Prairie Rattlesnake (Crotalus viridis viridis) to reconstruct, characterize, and infer the chromosomal locations of myotoxin-encoding loci. We integrate long-read transcriptomics (Pacific Bioscience's Iso-Seq) and short-read RNA-seq to infer gene sequence diversity and characterize patterns of myotoxin and paralogous β-defensin expression across multiple tissues. We also identify two long non-coding RNA sequences which both encode functional myotoxins, demonstrating a newly discovered source of venom coding sequence diversity. We also integrate long-range mate-pair chromatin contact data and linked-read sequencing to infer the structure and chromosomal locations of the three myotoxin-like loci. Further, we conclude that the venom-associated myotoxin is located on chromosome 1 and is adjacent to non-venom paralogs. Consistent with this locus contributing to venom composition, we find evidence that the promoter of this gene is selectively open in venom gland tissue and contains transcription factor binding sites implicated in broad trans-regulatory pathways that regulate snake venoms. This study provides the best genomic reconstruction of myotoxin loci to date and raises questions about the physiological roles and interplay between myotoxin and related genes, as well as the genomic origins of snake venom variation.

Proteomic analysis reveals rattlesnake venom modulation of proteins associated with cardiac tissue damage in mouse hearts

Snake envenomation is a common but neglected disease that affects millions of people around the world annually. Among venomous snake species in Brazil, the tropical rattlesnake (Crotalus durissus terrificus) accounts for the highest number of fatal envenomations and is responsible for the second highest number of bites. Snake venoms are complex secretions which, upon injection, trigger diverse physiological effects that can cause significant injury or death. The components of C. d. terrificus venom exhibit neurotoxic, myotoxic, hemotoxic, nephrotoxic, and cardiotoxic properties which present clinically as alteration of central nervous system function, motor paralysis, seizures, eyelid ptosis, ophthalmoplesia, blurred vision, coagulation disorders, rhabdomyolysis, myoglobinuria, and cardiorespiratory arrest. In this study, we focused on proteomic characterization of the cardiotoxic effects of C. d. terrificus venom in mouse models. We injected venom at half the lethal dose (LD50) into the gastrocnemius muscle. Mouse hearts were removed at set time points after venom injection (1 h, 6 h, 12 h, or 24 h) and subjected to trypsin digestion prior to high-resolution mass spectrometry. We analyzed the proteomic profiles of >1300 proteins and observed that several proteins showed noteworthy changes in their quantitative profiles, likely reflecting the toxic activity of venom components. Among the affected proteins were several associated with cellular deregulation and tissue damage. Changes in heart protein abundance offer insights into how they may work synergistically upon envenomation. SIGNIFICANCE: Venom of the tropical rattlesnake (Crotalus durissus terririficus) is known to be neurotoxic, myotoxic, nephrotoxic and cardiotoxic. Although there are several studies describing the biochemical effects of this venom, no work has yet described its proteomic effects in the cardiac tissue of mice. In this work, we describe the changes in several mouse cardiac proteins upon venom treatment. Our data shed new light on the clinical outcome of the envenomation by C. d. terrificus, as well as candidate proteins that could be investigated in efforts to improve current treatment approaches or in the development of novel therapeutic interventions in order to reduce mortality and morbidity resulting from envenomation.

Antimicrobial Activity of Snake β-Defensins and Derived Peptides

β-defensins are antimicrobial peptides presenting in vertebrate animals. They participate in innate immunity, but little is known about them in reptiles, including snakes. Although several β-defensin genes were described in Brazilian snakes, their function is still unknown. The peptide sequence from these genes was deduced, and synthetic peptides (with approximately 40 amino acids and derived peptides) were tested against pathogenic bacteria and fungi using microbroth dilution assays. The linear peptides, derived from β-defensins, were designed applying the bioisosterism strategy. The linear β-defensins were more active against Escherichia coli, Micrococcus luteus, Citrobacter freundii, and Staphylococcus aureus. The derived peptides (7–14 mer) showed antibacterial activity against those bacteria and on Klebsiella pneumoniae. Nonetheless, they did not present activity against Candida albicans, Cryptococcus neoformans, Trychophyton rubrum, and Aspergillus fumigatus showing that the cysteine substitution to serine is deleterious to antifungal properties. Tryptophan residue showed to be necessary to improve antibacterial activity. Even though the studied snake β-defensins do not have high antimicrobial activity, they proved to be attractive as template molecules for the development of antibiotics.

Revisiting the potential of South American rattlesnake Crotalus durissus terrificus toxins as therapeutic, theranostic and/or biotechnological agents

The potential biotechnological and biomedical applications of the animal venom components are widely recognized. Indeed, many components have been used either as drugs or as templates/prototypes for the development of innovative pharmaceutical drugs, among which many are still used for the treatment of human diseases. A specific South American rattlesnake, named Crotalus durissus terrificus, shows a venom composition relatively simpler compared to any viper or other snake species belonging to the Crotalus genus, although presenting a set of toxins with high potential for the treatment of several still unmet human therapeutic needs, as reviewed in this work. In addition to the main toxin named crotoxin, which is under clinical trials studies for antitumoral therapy and which has also anti-inflammatory and immunosuppressive activities, other toxins from the C. d. terrificus venom are also being studied, aiming for a wide variety of therapeutic applications, including as antinociceptive, anti-inflammatory, antimicrobial, antifungal, antitumoral or antiparasitic agent, or as modulator of animal metabolism, fibrin sealant (fibrin glue), gene carrier or theranostic agent. Among these rattlesnake toxins, the most relevant, considering the potential clinical applications, are crotamine, crotalphine and gyroxin. In this narrative revision, we propose to organize and present briefly the updates in the accumulated knowledge on potential therapeutic applications of toxins collectively found exclusively in the venom of this specific South American rattlesnake, with the objective of contributing to increase the chances of success in the discovery of drugs based on toxins.

Antimicrobial peptidomes of Bothrops atrox and Bothrops jararacussu snake venoms

The worrisome emergence of pathogens resistant to conventional drugs has stimulated the search for new classes of antimicrobial and antiparasitic agents from natural sources. Antimicrobial peptides (AMPs), acting through mechanisms that do not rely on the interaction with a specific receptor, provide new possibilities for the development of drugs against resistant organisms. This study sought to purify and proteomically characterize the antimicrobial and antiparasitic peptidomes of B. atrox and B. jararacussu snake venoms against Gram-positive (Staphylococcus aureus, Methicillin-resistant Staphylococcus aureus-MRSA), Gram-negative (Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae) bacteria, and the protozoan parasites Leishmania amazonensis and Plasmodium falciparum (clone W2, resistant to chloroquine). To this end, B. atrox and B. jararacussu venom peptides were purified by combination of 3 kDa cut-off Amicon^® ultracentrifugal filters and reverse-phase high-performance liquid chromatography, and then identified by electrospray-ionization Ion-Trap/Time-of-Flight mass spectrometry. Fourteen distinct peptides, with masses ranging from 443.17 to 1383.73 Da and primary structure between 3 and 13 amino acid residues, were sequenced. Among them, 13 contained unique sequences, including 4 novel bradykinin-potentiating-like peptides (BPPs), and a snake venom metalloproteinase tripeptide inhibitor (SVMPi). Although commonly found in Viperidae venoms, except for Bax-12, the BPPs and SVMPi here reported had not been described in B. atrox and B. jararacussu venoms. Among the novel peptides, some exhibited bactericidal activity towards P. aeruginosa and S. aureus, had low hemolytic effect, and were devoid of antiparasitic activity. The identified novel antimicrobial peptides may be relevant in the development of new drugs for the management of multidrug-resistant Gram-negative and Gram-positive bacteria.

Crotalus Durissus Ruruima: Current Knowledge on Natural History, Medical Importance, and Clinical Toxinology

Crotalus durissus ruruima is a rattlesnake subspecies mainly found in Roraima, the northernmost state of Brazil. Envenomings caused by this subspecies lead to severe clinical manifestations (e.g. respiratory muscle paralysis, rhabdomyolysis, and acute renal failure) that can lead to the victim’s death. In this review, we comprehensively describe C. d. ruruima biology and the challenges this subspecies poses for human health, including morphology, distribution, epidemiology, venom cocktail, clinical envenoming, and the current and future specific treatment of envenomings by this snake. Moreover, this review presents maps of the distribution of the snake subspecies and evidence that this species is responsible for some of the most severe envenomings in the country and causes the highest lethality rates. Finally, we also discuss the efficacy of the Brazilian horse-derived antivenoms to treat C. d. ruruima envenomings in Roraima state.

Acute toxicity, antinociceptive, and anti-inflammatory activities of the orally administered crotamine in mice

Crotamine is a polypeptide toxin isolated from rattlesnake venom. Although several studies have been developed identifying many biological effects of isolated crotamine, none of them evaluated its acute toxicity, antinociceptive, and anti-inflammatory activities through oral administration. All in vivo experiments from this study were performed in mice. The up-and-down procedure and hippocratic screening were carried out to evaluate possible pharmacological and toxic effects. Antinociceptive and anti-inflammatory activities of this toxin were evaluated using acetic acid-induced abdominal writhing, formalin-induced pain assays, croton oil-induced ear edema, and carrageenan-induced pleurisy. Crotamine did not cause lethality or signs of intoxication up to the maximum dose tested (10.88 mg/kg). The number of contortions was reduced significantly by 34, 57, and 74% at the oral doses of 0.08, 0.16, and 0.32 mg/kg, respectively. At the dose of 0.16 mg/kg, crotamine decreases pain time-reactivity at neurogenic phase by 45% and at inflammatory phase by 60%. Also, crotamine elicited antiedematogenic activity through the attenuation of the croton oil-induced ear edema by 77%. In the carrageenan-induced pleurisy, the leukocyte, neutrophil, and mononuclear cell migration to the lesion site were reduced by 52%, 46%, and 59%, respectively. Altogether, crotamine demonstrated in vivo antinociceptive and anti-inflammatory effect through acute oral administration, generating an anti-migratory mechanism of action at non-toxic doses.

Neutralization of crotamine by polyclonal antibodies generated against two whole rattlesnake venoms and a novel recombinant fusion protein

Crotamine is a paralyzing toxin (MW: ~5 kDa) found in different proportions in some rattlesnake venoms (up to 62%). Mexican pit viper antivenoms have shown low immunoreactivity against crotamine, which is an urgent quality to be improved. The objective of this work was to evaluate the ability of a novel recombinant fusion protein composed of sphingomyelinase D and crotamine, and two whole venoms from Crotalus molossus nigrescens and C. oreganus helleri to produce neutralizing antibodies against crotamine. These immunogens were separately used for immunization procedures in rabbits. Then, we generated three experimental antivenoms to test their cross-reactivity via western-blot against crotamine from 7 species (C. m. nigrescens, C. o. helleri, C. durissus terrificus, C. scutulatus salvini, C. basiliscus, C. culminatus and C. tzabcan). We also performed pre-incubation neutralization experiments in mice to measure the neutralizing potency of each antivenom against crotamine induced hind limb paralysis. Our antivenoms showed broad recognition across crotamine from most of the tested species. Also, neutralization against crotamine paralysis symptom was successfully achieved by our three antivenoms, albeit with different efficiencies. Our results highlight the use of crotamine enriched venoms and our novel recombinant fusion protein as promising immunogens to improve the neutralizing potency against crotamine for the improvement of Mexican antivenoms.

Cell-Penetrating Peptides Derived from Animal Venoms and Toxins

Cell-penetrating peptides (CPPs) comprise a class of short polypeptides that possess the ability to selectively interact with the cytoplasmic membrane of certain cell types, translocate across plasma membranes and accumulate in the cell cytoplasm, organelles (e.g., the nucleus and mitochondria) and other subcellular compartments. CPPs are either of natural origin or de novo designed and synthesized from segments and patches of larger proteins or designed by algorithms. With such intrinsic properties, along with membrane permeation, translocation and cellular uptake properties, CPPs can intracellularly convey diverse substances and nanomaterials, such as hydrophilic organic compounds and drugs, macromolecules (nucleic acids and proteins), nanoparticles (nanocrystals and polyplexes), metals and radionuclides, which can be covalently attached via CPP N- and C-terminals or through preparation of CPP complexes. A cumulative number of studies on animal toxins, primarily isolated from the venom of arthropods and snakes, have revealed the cell-penetrating activities of venom peptides and toxins, which can be harnessed for application in biomedicine and pharmaceutical biotechnology. In this review, I aimed to collate examples of peptides from animal venoms and toxic secretions that possess the ability to penetrate diverse types of cells. These venom CPPs have been chemically or structurally modified to enhance cell selectivity, bioavailability and a range of target applications. Herein, examples are listed and discussed, including cysteine-stabilized and linear, α-helical peptides, with cationic and amphipathic character, from the venom of insects (e.g., melittin, anoplin, mastoparans), arachnids (latarcin, lycosin, chlorotoxin, maurocalcine/imperatoxin homologs and wasabi receptor toxin), fish (pardaxins), amphibian (bombesin) and snakes (crotamine and cathelicidins).

Biological activities of a new crotamine-like peptide from Crotalus oreganus helleri on C2C12 and CHO cell lines, and ultrastructural changes on motor endplate and striated muscle

Crotamine and crotamine-like peptides are non-enzymatic polypeptides, belonging to the family of myotoxins, which are found in high concentration in the venom of the Crotalus genus. Helleramine was isolated and purified from the venom of the Southern Pacific rattlesnake, Crotalus oreganus helleri. This peptide had a similar, but unique, identity to crotamine and crotamine-like proteins isolated from other rattlesnakes species. The variability of crotamine-like protein amino acid sequences may allow different toxic effects on biological targets or optimize the action against the same target of different prey. Helleramine was capable of increasing intracellular Ca2+ in Chinese Hamster Ovary (CHO) cell line. It inhibited cell migration as well as cell viability (IC50 = 11.44 μM) of C2C12, immortalized skeletal myoblasts, in a concentration dependent manner, and promoted early apoptosis and cell death under our experimental conditions. Skeletal muscle harvested from mice 24 h after helleramine injection showed contracted myofibrils and profound vacuolization that enlarged the subsarcolemmal space, along with loss of plasmatic and basal membrane integrity. The effects of helleramine provide further insights and evidence of myotoxic activities of crotamine-like peptides and their possible role in crotalid envenomings.

Comparative proteomic profiling and functional characterization of venom pooled from captive Crotalus durissus terrificus specimens and the Brazilian crotalic reference venom

The South American rattlesnake Crotalus durissus spp has a wide geographic distribution in Brazil. Although responsible for only a low proportion of ophidian accidents, it is considered one of the most medically important species of venomous snakes due to the high mortality rate (1.87%). Snake venom is a complex phenotype commonly subjected to individual intraspecific, ontogenetic and geographic variability. Compositional differences in pooled venom used in the immunization process may impact the efficacy of the antivenom. In order to assure standardized high-quality antivenom, the potency of each Brazilian crotalic antivenom batch is determined against the 'Brazilian Crotalic Reference Venom' (BCRV). BCRV is produced by Instituto Butantan using venom obtained from the first milking of recently wild-caught C. d. terrificus specimens brought to the Institute. The decrease in the number of snake donations experienced in recent years can become a threat to the production of future batches of BCRV. To evaluate the feasibility of using venom from long-term captive animals in the formulation of BCRV, we have compared the proteomic, biochemical and biological profiles of C. d. terrificus venom pooled from captive specimens (CVP- captive venom pool) and BCRV. Electrophoretic and venomics analyses revealed a very similar venom composition profile, but also certain differences in toxins abundance, with some low abundant protein families found only in BCRV. Enzymatic (L-amino acid oxidase, phospholipase A₂ and proteolytic) and biological (myotoxic and coagulant) activities showed higher values in CVP than in BCRV. CVP also possessed slightly higher lethal effect, although the Instituto Butantan crotalic antivenom showed equivalent potency neutralizing BCRV and CVP. Our results strongly suggest that venom from long-term captive C. d. terrificus might be a valid alternative to generate an immunization mixture of equivalent quality to the currently in use reference venom.

Crotamine in Crotalus durissus: distribution according to subspecies and geographic origin, in captivity or nature

Background:

Crotalus durissus is considered one of the most important species of venomous snakes in Brazil, due to the high mortality of its snakebites. The venom of Crotalus durissus contains four main toxins: crotoxin, convulxin, gyroxin and crotamine. Venoms can vary in their crotamine content, being crotamine-negative or -positive. This heterogeneity is of great importance for producing antivenom, due to their different mechanisms of action. The possibility that antivenom produced by Butantan Institute might have a different immunorecognition capacity between crotamine-negative and crotamine-positive C. durissus venoms instigated us to investigate the differences between these two venom groups.

Methods:

The presence of crotamine was analyzed by SDS-PAGE, western blotting and ELISA, whereas comparison between the two types of venoms was carried out through HPLC, mass spectrometry analysis as well as assessment of antivenom lethality and efficacy.

Results:

The results showed a variation in the presence of crotamine among the subspecies and the geographic origin of snakes from nature, but not in captive snakes. Regarding differences between crotamine-positive and -negative venoms, some exclusive proteins are found in each pool and the crotamine-negative pool presented more phospholipase A₂ than crotamine-positive pool. This variation could affect the time to death, but the lethal and effective dose were not affected.

Conclusion:

These differences between venom pools indicate the importance of using both, crotamine-positive and crotamine-negative venoms, to produce the antivenom.

Ontogenetic Change in the Venom of Mexican Black-Tailed Rattlesnakes (Crotalus molossus nigrescens)

Ontogenetic changes in venom composition have important ecological implications due the relevance of venom in prey acquisition and defense. Additionally, intraspecific venom variation has direct medical consequences for the treatment of snakebite. However, ontogenetic changes are not well documented in most species. The Mexican Black-tailed Rattlesnake (Crotalus molossus nigrescens) is large-bodied and broadly distributed in Mexico. To document venom variation and test for ontogenetic changes in venom composition, we obtained venom samples from twenty-seven C. m. nigrescens with different total body lengths (TBL) from eight states in Mexico. The primary components in the venom were detected by reverse-phase HPLC, western blot, and mass spectrometry. In addition, we evaluated the biochemical (proteolytic, coagulant and fibrinogenolytic activities) and biological (LD₅₀ and hemorrhagic activity) activities of the venoms. Finally, we tested for recognition and neutralization of Mexican antivenoms against venoms of juvenile and adult snakes. We detected clear ontogenetic venom variation in C. m. nigrescens. Venoms from younger snakes contained more crotamine-like myotoxins and snake venom serine proteinases than venoms from older snakes; however, an increase of snake venom metalloproteinases was detected in venoms of larger snakes. Venoms from juvenile snakes were, in general, more toxic and procoagulant than venoms from adults; however, adult venoms were more proteolytic. Most of the venoms analyzed were hemorrhagic. Importantly, Mexican antivenoms had difficulties recognizing low molecular mass proteins (<12 kDa) of venoms from both juvenile and adult snakes. The antivenoms did not neutralize the crotamine effect caused by the venom of juveniles. Thus, we suggest that Mexican antivenoms would have difficulty neutralizing some human envenomations and, therefore, it may be necessary improve the immunization mixture in Mexican antivenoms to account for low molecular mass proteins, like myotoxins.

Antivenomic approach of different Crotalus durissus collilineatus venoms

BACKGROUND

Our group has previously performed a proteomic study verifying that individual variations can occur among Crotalus durissus collilineatus venoms. These variations may lead to differences in venom toxicity and may result in lack of neutralization of some components by antivenom. In this way, this study aimed to evaluate the Brazilian anticrotalic serum capacity in recognizing twenty-two Crotalus durissus collilineatus venoms, as well as their fractions.

METHODS

The indirect enzyme-linked immunosorbent assay (ELISA) was chosen to evaluate the efficacy of heterologous anticrotalic serum produced by Instituto Butantan (Brazil) in recognizing the twenty-two Crotalus durissus collilineatus venoms and the pool of them. Moreover, the venom pool was fractionated using reversed-phase fast protein liquid chromatography (RP-FPLC) and the obtained fractions were analyzed concerning antivenom recognition.

RESULTS

Evaluation of venom variability by ELISA showed that all venom samples were recognized by the Brazilian anticrotalic antivenom. However, some particular venom fractions were poorly recognized.

CONCLUSION

This study demonstrated that the Brazilian anticrotalic serum recognizes all the different twenty-two venoms of C. d. collilineatus and their fractions, although in a quantitatively different way, which may impact the effectiveness of the antivenom therapy. These results confirm the need to use a pool of venoms with the greatest possible variability in the preparation of antivenoms, in order to improve their effectiveness.

Non-neurotoxic activity of Malayan krait (Bungarus candidus) venom from Thailand

Background

Envenoming by kraits (genus Bungarus) is a medically significant issue in South Asia and Southeast Asia. Malayan krait (Bungarus candidus) venom is known to contain highly potent neurotoxins. In recent years, there have been reports on the non-neurotoxic activities of krait venom that include myotoxicity and nephrotoxicity. However, research on such non-neurotoxicity activities of Malayan krait venom is extremely limited. Thus, the aim of the present study was to determine the myotoxic, cytotoxic and nephrotoxic activities of B. candidus venoms from northeastern (BC-NE) and southern (BC-S) Thailand in experimentally envenomed rats.

Methods

Rats were administered Malayan krait (BC-NE or BC-S) venom (50 μg/kg, i.m.) or 0.9% NaCl solution (50 μL, i.m.) into the right hind limb. The animals were sacrificed 3, 6 and 24 h after venom administration. The right gastrocnemius muscle and both kidneys were collected for histopathological analysis. Blood samples were also taken for determination of creatine kinase (CK) and lactate dehydrogenase (LDH) levels. The human embryonic kidney cell line (HEK-293) was used in a cell proliferation assay to determine cytotoxic activity.

Results

Administration of BC-NE or BC-S venom (50 μg/kg, i.m.) caused time-dependent myotoxicity, characterized by an elevation of CK and LDH levels. Histopathological examination of skeletal muscle displayed marked muscle necrosis and myofiber disintegration 24 h following venom administration. Both Malayan krait venoms also induced extensive renal tubular injury with glomerular and interstitial congestion in rats. BC-NE and BC-S venoms (100–0.2 μg/mL) caused concentration-dependent cytotoxicity on the HEK-293 cell line. However, BC-NE venom (IC₅₀ = 8 ± 1 μg/mL; at 24 h incubation; n = 4) was found to be significantly more cytotoxic than BC-S venom (IC₅₀ = 15 ± 2 μg/mL; at 24 h incubation; n = 4). In addition, the PLA₂ activity of BC-NE venom was significantly higher than that of BC-S venom.

Conclusions

This study found that Malayan krait venoms from both populations possess myotoxic, cytotoxic and nephrotoxic activities. These findings may aid in clinical diagnosis and treatment of envenomed patients in the future.

Computational Studies of Snake Venom Toxins

Most snake venom toxins are proteins, and participate to envenomation through a diverse array of bioactivities, such as bleeding, inflammation, and pain, cytotoxic, cardiotoxic or neurotoxic effects. The venom of a single snake species contains hundreds of toxins, and the venoms of the 725 species of venomous snakes represent a large pool of potentially bioactive proteins. Despite considerable discovery efforts, most of the snake venom toxins are still uncharacterized. Modern bioinformatics tools have been recently developed to mine snake venoms, helping focus experimental research on the most potentially interesting toxins. Some computational techniques predict toxin molecular targets, and the binding mode to these targets. This review gives an overview of current knowledge on the ~2200 sequences, and more than 400 three-dimensional structures of snake toxins deposited in public repositories, as well as of molecular modeling studies of the interaction between these toxins and their molecular targets. We also describe how modern bioinformatics have been used to study the snake venom protein phospholipase A2, the small basic myotoxin Crotamine, and the three-finger peptide Mambalgin.

Integrated Venomics and Venom Gland Transcriptome Analysis of Juvenile and Adult Mexican Rattlesnakes Crotalus simus, C. tzabcan, and C. culminatus Revealed miRNA-modulated Ontogenetic Shifts

Adult rattlesnakes within genus Crotalus express one of two distinct venom phenotypes, type I (hemorrhagic) and type II (neurotoxic). In Costa Rican Central American rattlesnake, ontogenetic changes in the concentration of miRNAs modulate venom type II to type I transition. Venomics and venom gland transcriptome analyses showed that adult C. simus and C. tzabcan expressed intermediate patterns between type II and type I venoms, whereas C. culminatus had a canonical type I venom. Neonate/juvenile and adult Mexican rattlesnakes showed notable inter- and intraspecific variability in the number, type, abundance and ontogenetic shifts of the transcriptional and translational venom gland activities. These results support a role for miRNAs in the ontogenetic venom compositional changes in the three congeneric Mexican rattlesnakes. It is worth noting the finding of dual-action miRNAs, which silence the translation of neurotoxic heterodimeric PLA₂ crotoxin and acidic PLA₂ mRNAs while simultaneously up-regulating SVMP-targeting mRNAs. Dual transcriptional regulation potentially explains the existence of mutually exclusive crotoxin-rich (type-II) and SVMP-rich (type-I) venom phenotypic dichotomy among rattlesnakes. Our results support the hypothesis that alterations of the distribution of miRNAs, modulating the translational activity of venom gland toxin-encoding mRNAs in response to an external cue, may contribute to the mechanism generating adaptive venom variability.

Antivenomics as a tool to improve the neutralizing capacity of the crotalic antivenom: a study with crotamine

Background

Snakebite treatment requires administration of an appropriate antivenom that should contain antibodies capable of neutralizing the venom. To achieve this goal, antivenom production must start from a suitable immunization protocol and proper venom mixtures. In Brazil, antivenom against South American rattlesnake (Crotalus durissus terrificus) bites is produced by public institutions based on the guidelines defined by the regulatory agency of the Brazilian Ministry of Health, ANVISA. However, each institution uses its own mixture of rattlesnake venom antigens. Previous works have shown that crotamine, a toxin found in Crolatus durissus venom, shows marked individual and populational variation. In addition, serum produced from crotamine-negative venoms fails to recognize this molecule.

Methods

In this work, we used an antivenomics approach to assess the cross-reactivity of crotalic antivenom manufactured by IVB towards crotamine-negative venom and a mixture of crotamine-negative/crotamine-positive venoms.

Results

We show that the venom mixture containing 20% crotamine and 57% crotoxin produced a strong immunogenic response in horses. Antivenom raised against this venom mixture reacted with most venom components including crotamine and crotoxin, in contrast to the antivenom raised against crotamine-negative venom.

Conclusions

These results indicate that venomic databases and antivenomics analysis provide a useful approach for choosing the better venom mixture for antibody production and for the subsequent screening of antivenom cross-reactivity with relevant snake venom components.

[Relationships between venomous function and innate immune function]

Venomous function is investigated in relation to innate immune function in two cases selected from scorpion venom and serpent venom. In the first case, structural analysis of scorpion toxins and defensins reveals a close interrelation between both functions (toxic and innate immune system function). In the second case, structural and functional studies of natural inhibitors of toxic snake venom phospholipases A2 reveal homology with components of the innate immune system, leading to a similar conclusion. Although there is a clear functional distinction between neurotoxins, which act by targeting membrane ion channels, and the circulating defensins which protect the organism from pathogens, the scorpion short toxins and defensins share a common protein folding scaffold with a conserved cysteine-stabilized alpha-beta motif of three disulfide bridges linking a short alpha helix and an antiparallel beta sheet. Genomic analysis suggests that these proteins share a common ancestor (long venom toxins were separated from an early gene family which gave rise to separate short toxin and defensin families). Furthermore, a scorpion toxin has been experimentally synthetized from an insect defensin, and an antibacterial scorpion peptide, androctonin (whose structure is similar to that of a cone snail venom toxin), was shown to have a similar high affinity for the postsynaptic acetylcholine receptor of Torpedo sp. Natural inhibitors of phospholipase A2 found in the blood of snakes are associated with the resistance of venomous snakes to their own highly neurotoxic venom proteins. Three classes of phospholipases A2 inhibitors (PLI-α, PLI-β, PLI-γ) have been identified. These inhibitors display diverse structural motifs related to innate immune proteins including carbohydrate recognition domains (CRD), leucine rich repeat domains (found in Toll-like receptors) and three finger domains, which clearly differentiate them from components of the adaptive immune system. Thus, in structure, function and phylogeny, venomous function in both vertebrates and invertebrates are clearly interrelated with innate immune function.

Identification and Characterization of the First Cathelicidin from Sea Snakes with Potent Antimicrobial and Anti-inflammatory Activity and Special Mechanism

Cathelicidins are a family of gene-encoded peptide effectors of innate immunity found exclusively in vertebrates. They play pivotal roles in host immune defense against microbial invasions. Dozens of cathelicidins have been identified from several vertebrate species. However, no cathelicidin from marine reptiles has been characterized previously. Here we report the identification and characterization of a novel cathelicidin (Hc-CATH) from the sea snake Hydrophis cyanocinctus. Hc-CATH is composed of 30 amino acids, and the sequence is KFFKRLLKSVRRAVKKFRKKPRLIGLSTLL. Circular dichroism spectroscopy and structure modeling analysis indicated that Hc-CATH mainly assumes an amphipathic α-helical conformation in bacterial membrane-mimetic solutions. It possesses potent broad-spectrum and rapid antimicrobial activity. Meanwhile, it is highly stable and shows low cytotoxicity toward mammalian cells. The microbial killing activity of Hc-CATH is executed through the disruption of cell membrane and lysis of bacterial cells. In addition, Hc-CATH exhibited potent anti-inflammatory activity by inhibiting the LPS-induced production of nitric oxide (NO) and pro-inflammatory cytokines such as TNF-α, IL-1β, and IL-6. Hc-CATH directly binds with LPS to neutralize its toxicity, and it also binds to Toll-like receptor 4 (TLR4/MD2 complex), which therefore inhibits the binding of LPS to TLR4/MD2 complex and the subsequent activation of LPS-induced inflammatory response pathways. Taken together, our study demonstrates that Hc-CATH, the first cathelicidin from sea snake discovered to have both antimicrobial and anti-inflammatory activity, is a potent candidate for the development of peptide antibiotics.

Privileged frameworks from snake venom

Venom as a form of chemical prey capture is a key innovation that has underpinned the explosive radiation of the advanced snakes (Caenophidia). Small venom proteins are often rich in disulfide bonds thus facilitating stable molecular scaffolds that present key functional residues on the protein surface. New toxin types are initially developed through the venom gland over-expression of normal body proteins, their subsequent gene duplication and diversification that leads to neofunctionalisation as random mutations modify their structure and function. This process has led to preferentially selected (privileged) cysteine-rich scaffolds that enable the snake to build arrays of toxins many of which may lead to therapeutic products and research tools. This review focuses on cysteine-rich small proteins and peptides found in snake venoms spanning natriuretic peptides to phospholipase enzymes, while highlighting their three-dimensional structures and biological functions as well as their potential as therapeutic agents or research tools.

Testing the Toxicofera: comparative transcriptomics casts doubt on the single, early evolution of the reptile venom system

The identification of apparently conserved gene complements in the venom and salivary glands of a diverse set of reptiles led to the development of the Toxicofera hypothesis - the single, early evolution of the venom system in reptiles. However, this hypothesis is based largely on relatively small scale EST-based studies of only venom or salivary glands and toxic effects have been assigned to only some putative Toxicoferan toxins in some species. We set out to examine the distribution of these proposed venom toxin transcripts in order to investigate to what extent conservation of gene complements may reflect a bias in previous sampling efforts. Our quantitative transcriptomic analyses of venom and salivary glands and other body tissues in five species of reptile, together with the use of available RNA-Seq datasets for additional species, shows that the majority of genes used to support the establishment and expansion of the Toxicofera are in fact expressed in multiple body tissues and most likely represent general maintenance or "housekeeping" genes. The apparent conservation of gene complements across the Toxicofera therefore reflects an artefact of incomplete tissue sampling. We therefore conclude that venom has evolved multiple times in reptiles.

Intrahippocampal infusion of crotamine isolated from Crotalus durissus terrificus alters plasma and brain biochemical parameters

Crotamine is one of the main constituents of the venom of the South American rattlesnake Crotalus durissus terrificus. Here we sought to investigate the inflammatory and toxicological effects induced by the intrahippocampal administration of crotamine isolated from Crotalus whole venom. Adult rats received an intrahippocampal infusion of crotamine or vehicle and were euthanized 24 h or 21 days after infusion. Plasma and brain tissue were collected for biochemical analysis. Complete blood count, creatinine, urea, glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), creatine-kinase (CK), creatine kinase-muscle B (CK-MB) and oxidative parameters (assessed by DNA damage and micronucleus frequency in leukocytes, lipid peroxidation and protein carbonyls in plasma and brain) were quantified. Unpaired and paired t-tests were used for comparisons between saline and crotamine groups, and within groups (24 h vs. 21 days), respectively. After 24 h crotamine infusion promoted an increase of urea, GOT, GPT, CK, and platelets values (p ≤ 0.01), while red blood cells, hematocrit and leukocytes values decreased (p ≤ 0.01). Additionally, 21 days after infusion crotamine group showed increased creatinine, leukocytes, TBARS (plasma and brain), carbonyl (plasma and brain) and micronucleus compared to the saline-group (p ≤ 0.01). Our findings show that crotamine infusion alter hematological parameters and cardiac markers, as well as oxidative parameters, not only in the brain, but also in the blood, indicating a systemic pro-inflammatory and toxicological activity. A further scientific attempt in terms of preserving the beneficial activity over toxicity is required.

Membrane-modifying properties of crotamine, a small peptide-toxin from Crotalus durissus terifficus venom

BACKGROUND

Crotamine is a small, highly basic myotoxin from the venom of the South American rattlesnake Crotalus durissus terifficus. It is structurally well defined and exhibits some similarities with the β-defensins of vertebrates. An amazing variety of functions and targets that range from analgesia and tumor-related activity to cell penetration have been associated with crotamine. Similar to defensins, it had been argued that crotamine has antimicrobial activity, and this supposition was recently proven.Moreover, it has been argued that the antimicrobial activity of crotamine is due to the membrane permeabilizing properties of the peptide. However, until now, the detailed mechanism of this postulated membrane permeabilization was still unclear.

METHODS

In this paper, we used gradient SDS-gels, mass spectroscopy (MALDI-TOF), and monolayer and planar lipid bilayer experiments to investigate the membrane modifying properties of crotamine.

RESULTS

We showed that crotamine itself forms stable monolayers because of its amphipathic structure, is easily incorporated into lipid monolayers and forms well-defined pores with low cationic selectivity in planar lipid bilayers; these properties might account for the antimicrobial activity of crotamine. The pores are probably oligomericaggregates of crotamine molecules, as suggested by the tendency of crotamine to form oligomers in aqueous solution and the fact that the structure of crotamine does not allow pore formation by monomers.

CONCLUSIONS

The membrane modifying and antimicrobial properties of crotamine are probably due to homo oligomeric pore formation in membranes.

GENERAL SIGNIFICANCE

The results should be highly interesting to researchers in the fields of biophysics, pharmacology,toxicology and antibiotics.

Quantitative high-throughput profiling of snake venom gland transcriptomes and proteomes (Ovophis okinavensis and Protobothrops flavoviridis)

Background

Advances in DNA sequencing and proteomics have facilitated quantitative comparisons of snake venom composition. Most studies have employed one approach or the other. Here, both Illumina cDNA sequencing and LC/MS were used to compare the transcriptomes and proteomes of two pit vipers, Protobothrops flavoviridis and Ovophis okinavensis, which differ greatly in their biology.

Results

Sequencing of venom gland cDNA produced 104,830 transcripts. The Protobothrops transcriptome contained transcripts for 103 venom-related proteins, while the Ovophis transcriptome contained 95. In both, transcript abundances spanned six orders of magnitude. Mass spectrometry identified peptides from 100% of transcripts that occurred at higher than contaminant (e.g. human keratin) levels, including a number of proteins never before sequenced from snakes. These transcriptomes reveal fundamentally different envenomation strategies. Adult Protobothrops venom promotes hemorrhage, hypotension, incoagulable blood, and prey digestion, consistent with mammalian predation. Ovophis venom composition is less readily interpreted, owing to insufficient pharmacological data for venom serine and metalloproteases, which comprise more than 97.3% of Ovophis transcripts, but only 38.0% of Protobothrops transcripts. Ovophis venom apparently represents a hybrid strategy optimized for frogs and small mammals.

Conclusions

This study illustrates the power of cDNA sequencing combined with MS profiling. The former quantifies transcript composition, allowing detection of novel proteins, but cannot indicate which proteins are actually secreted, as does MS. We show, for the first time, that transcript and peptide abundances are correlated. This means that MS can be used for quantitative, non-invasive venom profiling, which will be beneficial for studies of endangered species.

Neurotoxicity in snakebite--the limits of our knowledge

Snakebite is classified by the WHO as a neglected tropical disease. Envenoming is a significant public health problem in tropical and subtropical regions. Neurotoxicity is a key feature of some envenomings, and there are many unanswered questions regarding this manifestation. Acute neuromuscular weakness with respiratory involvement is the most clinically important neurotoxic effect. Data is limited on the many other acute neurotoxic manifestations, and especially delayed neurotoxicity. Symptom evolution and recovery, patterns of weakness, respiratory involvement, and response to antivenom and acetyl cholinesterase inhibitors are variable, and seem to depend on the snake species, type of neurotoxicity, and geographical variations. Recent data have challenged the traditional concepts of neurotoxicity in snake envenoming, and highlight the rich diversity of snake neurotoxins. A uniform system of classification of the pattern of neuromuscular weakness and models for predicting type of toxicity and development of respiratory weakness are still lacking, and would greatly aid clinical decision making and future research. This review attempts to update the reader on the current state of knowledge regarding this important issue.

Role of the inflammasome in defense against venoms

Venoms consist of a complex mixture of toxic components that are used by a variety of animal species for defense and predation. Envenomation of mammalian species leads to an acute inflammatory response and can lead to the development of IgE-dependent venom allergy. However, the mechanisms by which the innate immune system detects envenomation and initiates inflammatory and allergic responses to venoms remain largely unknown. Here we show that bee venom is detected by the NOD-like receptor family, pyrin domain-containing 3 inflammasome and can trigger activation of caspase-1 and the subsequent processing and unconventional secretion of the leaderless proinflammatory cytokine IL-1β in macrophages. Whereas activation of the inflammasome by bee venom induces a caspase-1-dependent inflammatory response, characterized by recruitment of neutrophils to the site or envenomation, the inflammasome is dispensable for the allergic response to bee venom. Finally, we find that caspase-1-deficient mice are more susceptible to the noxious effects of bee and snake venoms, suggesting that a caspase-1-dependent immune response can protect against the damaging effects of envenomation.

Purification, crystallization and preliminary X-ray diffraction analysis of crotamine, a myotoxic polypeptide from the Brazilian snake Crotalus durissus terrificus

Crotamine, a highly basic myotoxic polypeptide (molecular mass 4881 Da) isolated from the venom of the Brazilian rattlesnake Crotalus durissus terrificus, causes skeletal muscle contraction and spasms, affects the functioning of voltage-sensitive sodium channels by inducing sodium influx and possesses antitumour activity, suggesting potential pharmaceutical applications. Crotamine was purified from C. durissus terrificus venom; the crystals diffracted to 1.9 Å resolution and belonged to the orthorhombic space group I2(1)2(1)2(1) or I222, with unit-cell parameters a = 67.75, b = 74.4, c = 81.01 Å. The self-rotation function indicated that the asymmetric unit contained three molecules. However, structure determination by molecular replacement using NMR-determined coordinates was unsuccessful and a search for potential derivatives has been initiated.

Fatal Envenomations - Snakes and Other Creatures

Envenomations by toxic creatures is a global health problem with an annual mortality from snake envenomation of over 125,000 cases. While various snake species bites are the most commonly encountered fatal envenomation, scorpions, spiders and marine creatures can all cause fatalities. Although venomous creatures have specific geographical habitats, the keeping of exotic pets and modern transportation, along with venomous collections in zoos, means that fatal envenomations may be encountered in non-endemic areas. There are a variety of toxins that may be encountered including neurotoxins, proteases, and myotoxins that will result in a variable amount of tissue damage depending upon the species involved and the toxin they carry. The autopsy findings may be relatively nonspecific and a careful search of the skin may be required to identify the envenomation site, along with a consideration of the history and the scene. External and internal damage will vary with the specific toxin. This paper reviews fatal envenomations, the toxinology and likely autopsy findings.

The venom-gland transcriptome of the eastern diamondback rattlesnake (Crotalus adamanteus)

Background

Snake venoms have significant impacts on human populations through the morbidity and mortality associated with snakebites and as sources of drugs, drug leads, and physiological research tools. Genes expressed by venom-gland tissue, including those encoding toxic proteins, have therefore been sequenced but only with relatively sparse coverage resulting from the low-throughput sequencing approaches available. High-throughput approaches based on 454 pyrosequencing have recently been applied to the study of snake venoms to give the most complete characterizations to date of the genes expressed in active venom glands, but such approaches are costly and still provide a far-from-complete characterization of the genes expressed during venom production.

Results

We describe the de novo assembly and analysis of the venom-gland transcriptome of an eastern diamondback rattlesnake (Crotalus adamanteus) based on 95,643,958 pairs of quality-filtered, 100-base-pair Illumina reads. We identified 123 unique, full-length toxin-coding sequences, which cluster into 78 groups with less than 1% nucleotide divergence, and 2,879 unique, full-length nontoxin coding sequences. The toxin sequences accounted for 35.4% of the total reads, and the nontoxin sequences for an additional 27.5%. The most highly expressed toxin was a small myotoxin related to crotamine, which accounted for 5.9% of the total reads. Snake-venom metalloproteinases accounted for the highest percentage of reads mapping to a toxin class (24.4%), followed by C-type lectins (22.2%) and serine proteinases (20.0%). The most diverse toxin classes were the C-type lectins (21 clusters), the snake-venom metalloproteinases (16 clusters), and the serine proteinases (14 clusters). The high-abundance nontoxin transcripts were predominantly those involved in protein folding and translation, consistent with the protein-secretory function of the tissue.

Conclusions

We have provided the most complete characterization of the genes expressed in an active snake venom gland to date, producing insights into snakebite pathology and guidance for snakebite treatment for the largest rattlesnake species and arguably the most dangerous snake native to the United States of America, C. adamanteus. We have more than doubled the number of sequenced toxins for this species and created extensive genomic resources for snakes based entirely on de novo assembly of Illumina sequence data.

Venomics profiling of Thamnodynastes strigatus unveils matrix metalloproteinases and other novel proteins recruited to the toxin arsenal of rear-fanged snakes

Rear-fanged and aglyphous snakes are usually considered not dangerous to humans because of their limited capacity of injecting venom. Therefore, only a few studies have been dedicated to characterizing the venom of the largest parcel of snake fauna. Here, we investigated the venom proteome of the rear-fanged snake Thamnodynastes strigatus , in combination with a transcriptomic evaluation of the venom gland. About 60% of all transcripts code for putative venom components. A striking finding is that the most abundant type of transcript (∼47%) and also the major protein type in the venom correspond to a new kind of matrix metalloproteinase (MMP) that is unrelated to the classical snake venom metalloproteinases found in all snake families. These enzymes were recently suggested as possible venom components, and we show here that they are proteolytically active and probably recruited to venom from a MMP-9 ancestor. Other unusual proteins were suggested to be venom components: a protein related to lactadherin and an EGF repeat-containing transcript. Despite these unusual molecules, seven toxin classes commonly found in typical venomous snakes are also present in the venom. These results support the evidence that the arsenals of these snakes are very diverse and harbor new types of biologically important molecules.

In vitro antibacterial and hemolytic activities of crotamine, a small basic myotoxin from rattlesnake Crotalus durissus

Crotamine, a myotoxin from the venom of South American rattlesnake, is structurally related to β-defensins, antimicrobial peptides (AMPs) found in vertebrate animals. Here, we tested the antibacterial properties of crotamine and found that it killed several strains of Escherichia coli, with the MICs ranging from 25 to 100 μg ml⁻¹. Time-kill and bacterial membrane permeabilization assays revealed that killing of bacteria by crotamine occurred within 1 h and reached the maximum by 2 h. Additionally, the anti-E. coli activity of crotamine was completely abolished with 12.5 mM NaCl. Furthermore, the three intramolecular disulfide bonds of crotamine appeared dispensable for its antibacterial activity. The reduced form of crotamine was active against E. coli as well. However, crotamine showed no or weak activity up to 200 μg ml⁻¹ against other species of Gram-negative and Gram-positive bacteria. Crotamine showed no appreciable hemolytic activity to erythrocytes. Our studies revealed that crotamine is also an AMP that kills bacteria through membrane permeabilization. However, crotamine appears to have a narrow antibacterial spectrum, distinct from many classical β-defensins, reinforcing the notion that crotamine originated from the β-defensin gene lineage, but has undergone significant functional diversification.

On the venom system of centipedes (Chilopoda), a neglected group of venomous animals

Centipedes are among the oldest extant terrestrial arthropods and are an ecologically important group of soil and leaf litter predators. Despite their abundance and frequent, often painful, encounters with humans, little is known about the venom and venom apparatus of centipedes, although it is apparent that these are both quite different from other venomous lineages. The venom gland can be regarded as an invaginated cuticle and epidermis, consisting of numerous epithelial secretory units each with its own unique valve-like excretory system. The venom contains several different enzymes, but is strikingly different to most other arthropods in that metalloproteases appear to be important. Myotoxic, cardiotoxic, and neurotoxic activities have been described, most of which have been attributed to high molecular weight proteins. Neurotoxic activities are also unusual in that G-protein coupled receptors often seem to be involved, either directly as targets of neurotoxins or indirectly by activating endogenous agonists. These relatively slow responses may be complemented by the rapid effects caused by histamines present in the venom and from endogenous release of histamines induced by venom cytotoxins. The differences probably reflect the ancient and independent evolutionary history of the centipede venom system, although they may also be somewhat exaggerated by the paucity of information available on this largely neglected group.