Presence of peptide inhibitors in rattlesnake venoms and their effects on endogenous metalloproteases

Comparative Venom Proteomics of Iranian, Macrovipera lebetina cernovi, and Cypriot, Macrovipera lebetina lebetina, Giant Vipers

Envenoming by Macrovipera lebetina subspecies causes severe life-threatening difficulties for people living in North Africa and the Middle East. To better understand the pathophysiology of envenoming and improve patient management, knowledge about the venom components of the subspecies is essential. Here, the venom proteomes of Macrovipera lebetina lebetina from Cyprus and Macrovipera lebetina cernovi from Iran were characterized using RP-HPLC separation of the crude venom proteins, SDS-PAGE of fractionated proteins, and LC-MS/MS of peptides obtained from in-gel tryptic digestion of protein bands. Moreover, we also used high-resolution shot-gun proteomics to gain more reliable identification, where the whole venom proteomes were subjected directly to in-solution digestion before LC-HR-MS/MS. The data revealed that both venoms consisted of at least 18 protein families, of which snake venom Zn2+-dependent metalloprotease (SVMP), serine protease, disintegrin, phospholipase A2, C-type lectin-like, and L-amino acid oxidase, together accounted for more than 80% of the venoms’ protein contents. Although the two viper venoms shared mostly similar protein classes, the relative occurrences of these toxins were different in each snake subspecies. For instance, P-I class of SVMP toxins were found to be more abundant than P-III class in the venoms of M. l. cernovi compared to M. l. lebetina, which gives hints at a more potent myonecrotic effect and minor systemic hemorrhage following envenoming by M. l. cernovi than M. l. lebetina. Moreover, single-shot proteomics also revealed many proteins with low abundance (<1%) within the venoms, such as aminopeptidase, hyaluronidase, glutaminyl-peptide cyclotransferase, cystatin, phospholipase B, and vascular endothelial growth factor. Our study extends the in-depth understanding of the venom complexity of M. lebetina subspecies, particularly regarding toxin families associated with envenoming pathogenesis and those hard-detected protein classes expressed in trace amounts.

Convergent evolution of toxin resistance in animals

Convergence is the phenomenon whereby similar phenotypes evolve independently in different lineages. One example is resistance to toxins in animals. Toxins have evolved many times throughout the tree of life. They disrupt molecular and physiological pathways in target species, thereby incapacitating prey or deterring a predator. In response, molecular resistance has evolved in many species exposed to toxins to counteract their harmful effects. Here, we review current knowledge on the convergence of toxin resistance using examples from a wide range of toxin families. We explore the evolutionary processes and molecular adaptations driving toxin resistance. However, resistance adaptations may carry a fitness cost if they disrupt the normal physiology of the resistant animal. Therefore, there is a trade‐off between maintaining a functional molecular target and reducing toxin susceptibility. There are relatively few solutions that satisfy this trade‐off. As a result, we see a small set of molecular adaptations appearing repeatedly in diverse animal lineages, a phenomenon that is consistent with models of deterministic evolution. Convergence may also explain what has been called ‘autoresistance’. This is often thought to have evolved for self‐protection, but we argue instead that it may be a consequence of poisonous animals feeding on toxic prey. Toxin resistance provides a unique and compelling model system for studying the interplay between trophic interactions, selection pressures and the molecular mechanisms underlying evolutionary novelties.

Venom production and secretion in reptiles

The venom glands of reptiles, particularly those of front-fanged advanced snakes, must satisfy conflicting biological demands: rapid synthesis of potentially labile and highly toxic proteins, storage in the gland lumen for long periods, stabilization of the stored secretions, immediate activation of toxins upon deployment and protection of the animal from the toxic effects of its own venom. This dynamic system could serve as a model for the study of a variety of different phenomena involving exocrine gland activation, protein synthesis, stabilization of protein products and secretory mechanisms. However, these studies have been hampered by a lack of a long-term model that can be propagated in the lab (as opposed to whole-animal studies). Numerous attempts have been made to extend the lifetime of venom gland secretory cells, but only recently has an organoid model been shown to have the requisite qualities of recapitulation of the native system, self-propagation and long-term viability (>1 year). A tractable model is now available for myriad cell- and molecular-level studies of venom glands, protein synthesis and secretion. However, venom glands of reptiles are not identical, and many differ very extensively in overall architecture, microanatomy and protein products produced. This Review summarizes the similarities among and differences between venom glands of helodermatid lizards and of rear-fanged and front-fanged snakes, highlighting those areas that are well understood and identifying areas where future studies can fill in significant gaps in knowledge of these ancient, yet fascinating systems.

Venomics of the poorly studied hognosed pitvipers Porthidium arcosae and Porthidium volcanicum

We report the first proteomics analyses of the venoms of two poorly studied snakes, the Manabi hognosed pitviper Porthidium arcosae endemic to the western coastal province of Manabí (Ecuador), and the Costa Rican hognosed pitviper P. volcanicum with distribution restricted to South Pacific Costa Rica and western Panamá. These venom proteomes share a conserved compositional pattern reported in four other congeneric species within the clade of South American Porthidium species, P. nasutum, P. lansbergii, P. ophryomegas, and P. porrasi. The paraspecific immunorecognition profile of antivenoms produced in Costa Rica (ICP polyvalent), Perú (Instituto Nacional de Salud) and Brazil (soro antibotrópico pentavalente, SAB, from Instituto Butantan) against the venom of P. arcosae was investigated through a third-generation antivenomics approach. The maximal venom-binding capacities of the investigated antivenoms were 97.1 mg, 21.8 mg, and 25.7 mg of P. arcosae venom proteins per gram of SAB, ICP, and INS-PERU antibody molecules, respectively, which translate into 28.4 mg, 13.1 mg, and 15.2 mg of total venom proteins bound per vial of SAB, ICP, and INS-PERU AV. The antivenomics results suggest that 21.8%, 7.8% and 6.1% of the SAB, ICP, and INS-PERU antibody molecules recognized P. arcosae venom toxins. The SAB antivenom neutralized P. arcosae venom's lethality in mice with an ED₅₀ of 31.3 mgV/g SAB AV. This preclinical neutralization paraspecificity points to Brazilian SAB as a promising candidate for the treatment of envenomings by Ecuadorian P. arcosae. BIOLOGICAL SIGNIFICANCE: Assessing the preclinical efficacy profile of antivenoms against homologous and heterologous medically relevant snake venoms represents an important goal towards defining the biogeographic range of their clinical utility. This is particularly relevant in regions, such as Mesoamerica, where a small number of pharmaceutical companies produce antivenoms against the venoms of a small number of species of maximum medical relevance among the local rich herpetofauna, leaving a wide range of snakes of secondary medical relevance, but also causing life-threatening human envenomings without nominal clinical coverage. This work is part of a larger project aiming at mapping the immunological characteristics of antivenoms generated in Latin American countries towards venoms of such poorly studied snakes of the local and neighboring countries' herpetofauna. Here we report the proteomics characterization of the Manabi hognosed pitviper Porthidium arcosae endemic to the western coastal province of Manabí (Ecuador), and the Costa Rican hognosed pitviper P. volcanicum with distribution restricted to southwestern Costa Rica, the antivenomics assessment of three bothropoid commercial antivenoms produced in Costa Rica, Perú, and Brazil against the venom components of P. arcosae, and the in vivo capacity of the Brazilian soro antibotrópico pentavalente (SAB) from Instituto Butantan to neutralize the murine lethality of P. arcosae venom. The preclinical paraspecific ED₅₀ of 31.3 mg of P. arcosae venom per gram of antivenom points to Brazilian SAB as a promising candidate for the treatment of envenomings by the Manabi hognosed pitviper P. arcosae.

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.

Venom Gland Mass Spectrometry Imaging of Saw-Scaled Viper, Echis carinatus sochureki, at High Lateral Resolution

The snake venom gland is the place for the synthesis, storage, and secretion of a complex mixture of proteins and peptides, i.e., the venom. The morphology of the gland has been revealed by classical histology and microscopic studies. However, knowledge about the gland's cellular secretory and functional processes is still incomplete and has so far been neglected by the omics disciplines. We used autofocusing atmospheric-pressure matrix-assisted laser desorption/ionization (AP-SMALDI) mass spectrometry imaging (MSI) to investigate endogenous biomolecular distributions in the venom glands of the saw-scaled viper, Echis carinatus sochureki, employing different sample preparation methods. Fresh-freezing and formalin-fixation were tested for the gland to obtain intact tissue sections. Subsequently, MSI was conducted with 12 μm pixel resolution for both types of preparations, and the lateral distributions of the metabolites were identified. Experiments revealed that lipids belonging to the classes of PC, SM, PE, PS, PA, and TG are present in the venom gland. PC (32:0) and SM (36:1) were found to be specifically located in the areas where cells are present. The snake venom metalloprotease inhibitor pEKW (m/z 444.2233) was identified in the venom by top-down LC-MS/MS and localized by MALDI-MSI in the gland across secretory epithelial cells. The peptide can inhibit the venom's enzymatic activity during long-term storage within the venom gland. With a high degree of spectral similarities, we concluded that formalin-fixed tissue, in addition to its high ability to preserve tissue morphology, can be considered as an alternative method to fresh-frozen tissue in the case of lipid and peptide MS imaging in venom gland tissues.

Dagestan blunt-nosed viper, Macrovipera lebetina obtusa (Dwigubsky, 1832), venom. Venomics, antivenomics, and neutralization assays of the lethal and toxic venom activities by anti-Macrovipera lebetina turanica and anti-Vipera berus berus antivenoms

We have applied a combination of venomics, in vivo neutralization assays, and in vitro third-generation antivenomics analysis to assess the preclinical efficacy of the monospecific anti-Macrovipera lebetina turanica (anti-Mlt) antivenom manufactured by Uzbiopharm® (Uzbekistan) and the monospecific anti-Vipera berus berus antivenom from Microgen® (Russia) against the venom of Dagestan blunt-nosed viper, Macrovipera lebetina obtusa (Mlo). Despite their low content of homologous (anti-Mlt, 5–10%) or para-specific (anti-Vbb, 4–9%) F(ab')₂ antibody fragments against M. l. obtusa venom toxins, both antivenoms efficiently recognized most components of the complex venom proteome's arsenal, which is made up of toxins derived from 11 different gene families and neutralized, albeit at different doses, key toxic effects of M. l. obtusa venom, i.e., in vivo lethal and hemorrhagic effects in a murine model, and in vitro phospholipase A₂, proteolytic and coagulant activities. The calculated lethality neutralization potencies for Uzbiopharm® anti-Mlt and anti-Vbb Microgen® antivenoms were 1.46 and 1.77 mg/mL, indicating that 1 mL of Uzbiopharm® and Microgen® antivenoms may protect mice from 41 to 50 LD₅₀s of Mlo venom, respectively. The remarkable degree of conservation of immunogenic determinants between species of the clades of European and Oriental viper, which evolved geographically segregated since the early Miocene, suggests an eventual window of opportunity for the treatment of envenomings by Eurasian snakes. Clearly, the rational use of heterologous antivenoms requires establishing their para-specificity landscapes. This paper illustrates the analytical power of combining in vitro and in vivo preclinical quantitative assays toward this goal.

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Efficacy against M. l. obtusa venom by two antivenoms was investigated.

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Quantification of lethality neutralizing antibodies was assessed.

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Anti-Vipera berus antivenom showed paraspecificity against M. l. obtusa venom.

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This study provides hints as how to improve the potency of the antivenoms sampled.

Venomics and antivenomics of the poorly studied Brazil's lancehead, Bothrops brazili (Hoge, 1954), from the Brazilian State of Pará

Background:

The Brazil’s lancehead, Bothrops brazili, is a poorly studied pit viper distributed in lowlands of the equatorial rainforests of southern Colombia, northeastern Peru, eastern Ecuador, southern and southeastern Venezuela, Guyana, Suriname, French Guiana, Brazil, and northern Bolivia. Few studies have been reported on toxins isolated from venom of Ecuadorian and Brazilian B. brazili. The aim of the present study was to elucidate the qualitative and quantitative protein composition of B. brazili venom from Pará (Brazil), and to carry out a comparative antivenomics assessment of the immunoreactivity of the Brazilian antibothropic pentavalent antivenom [soro antibotrópico (SAB) in Portuguese] against the venoms of B. brazili and reference species, B. jararaca.

Methods:

We have applied a quantitative snake venomics approach, including reverse-phase and two-dimensional electrophoretic decomplexation of the venom toxin arsenal, LC-ESI-MS mass profiling and peptide-centric MS/MS proteomic analysis, to unveil the overall protein composition of B. brazili venom from Pará (Brazil). Using third-generation antivenomics, the specific and paraspecific immunoreactivity of the Brazilian SAB against homologous (B. jararaca) and heterologous (B. brazili) venoms was investigated.

Results:

The venom proteome of the Brazil’s lancehead (Pará) is predominantly composed of two major and three minor acidic (19%) and two major and five minor basic (14%) phospholipase A₂ molecules; 7-11 snake venom metalloproteinases of classes PI (21%) and PIII (6%); 10-12 serine proteinases (14%), and 1-2 L-amino acid oxidases (6%). Other toxins, including two cysteine-rich secretory proteins, one C-type lectin-like molecule, one nerve growth factor, one 5'-nucleotidase, one phosphodiesterase, one phospholipase B, and one glutaminyl cyclase molecule, represent together less than 2.7% of the venom proteome. Third generation antivenomics profile of the Brazilian pentabothropic antivenom showed paraspecific immunoreactivity against all the toxin classes of B. brazili venom, with maximal binding capacity of 132.2 mg venom/g antivenom. This figure indicates that 19% of antivenom's F(ab')₂ antibodies bind B. brazili venom toxins.

Conclusion:

The proteomics outcome contribute to a deeper insight into the spectrum of toxins present in the venom of the Brazil’s lancehead, and rationalize the pathophysiology underlying this snake bite envenomings. The comparative qualitative and quantitative immunorecognition profile of the Brazilian pentabothropic antivenom toward the venom toxins of B. brazili and B. jararaca (the reference venom for assessing the bothropic antivenom's potency in Brazil), provides clues about the proper use of the Brazilian antibothropic polyvalent antivenom in the treatment of bites by the Brazil’s lancehead.

Assessing the stability of historical and desiccated snake venoms from a medically important Ecuadorian collection

Bothrops asper and Bothrops atrox are important venomous snakes from Ecuador responsible for the most of ophidic accidents, which in the past were treated with a national polyvant antivenom. For years, the venom pools were collected and stored at room temperature in a laboratory. Taking into account the controversial ability of desiccated samples to retain their biological effects and enzymatic activities, we investigated the biochemical and toxicological properties of venoms after years of storage. The proteomic profiles of historical venoms analyzed by high-performance liquid chromatography and electrophoresis are very similar. The fresh batches of venom were more lethal than those stored for years, just as the initial and current LD₅₀ values of these samples changed. Significant differences were showed in the myotoxic and hemorrhagic activity of some venom pools, while no significant statistical differences were found for the edema activity. The enzymatic assays revealed a variation in proteolytic activity on azocasein and phospholipase A₂ activity, and low differences were reported for thrombin-like serine protease activity. The maintenance of the proteomic profile and certain toxicological activities convert this venom library in a valuable source for research purposes. Nonetheless, the significative reduction of toxicological activities, such as hemorrhagic activity not feasible using these samples for the antivenom production.

Natural Inhibitors of Snake Venom Metalloproteinases

Snakebites are a hazard in the tropical world. Although antivenom therapy is effective, it is beset with inherent drawbacks. A better understanding of the major components of snake venoms and their neutralisation will help in improving snakebite treatment. Snake venom metalloproteinases (SVMPs) are responsible for severe haemorrhage, the inhibition of coagulation and platelet aggregation, observed in the victims of snakebite envenoming. Inhibitors from various sources including medicinal plants, animal venoms, and sera are sought to block the pharmacological functions of SVMPs. In this review, we describe the interaction of natural inhibitors with SVMPs. To understand their inhibitory mechanisms, we focussed on the complex structures of these inhibitors and SVMPs. There are three distinct classes of inhibitors; namely, chelators, competitive inhibitors, and non-competitive inhibitors. A small number of inhibitors show their anti-hemorrhagic activity in invivo animal models in treatment mode, but most studies evaluate either invitro neutralisation of enzymatic activity or invivo effects in pre-incubation protocols. We propose the distinct strategies and limitations to design either broad-spectrum or highly selective SVMP inhibitors. The goal of designing broad-spectrum inhibitors against SVMPs capable of effective treatment of snakebites without toxicity has been elusive, probably because of the narrow molecular footprint of inhibitors against a large number of SVMPs with distinct molecular surfaces. Our ability to design highly selective inhibitors is limited by the lack of information of interactions between selective inhibitors and SVMPs. Comparisons of structures of hemorrhagic and non-hemorrhagic SVMPs revealed different distributions of electric charge on the surface of SVMPs, which may be exploited to design specific inhibitors. The specific inhibitors may also be useful to identify target molecules of the SVMPs and help to understand their mechanism of action.

Morphological alterations caused by manual venom extraction on the main venom gland of Bothrops asper and Crotalus simus snakes (Serpentes: Viperidae): Long-term implications for antivenom production

The only scientifically validated treatment for snakebite envenomation is the administration of antivenoms. For their production, small quantities of snake venom are injected in animals to elicit a specific antibody response. Snakes are kept in captivity, and their venom is regularly extracted to assure antivenom access. It has already been reported that the pressure exerted upon the venom gland during this extraction can cause tissue damage and fibrosis, leading to a decrease in the venom yield. We described the histopathology of venom glands for B. asper and C. simus snakes used for antivenom production. Based on these reported tissue abnormalities, we quantify the tissue injury by a generated damage-SCORE and fibrosis. A variety of histopathological damages were found such as fibrosis, edema, necrosis, hemorrhage, and formation of anomalous structures, especially in C. simus, which is more prone to suffer severe damage. The level and severity of the damage depend on the frequency and the number of venom extractions. Furthermore, we design an experimental intensive venom extraction scheme with which we could confirm the causality of these effects. In addition to the histopathological damages, the LD₅₀ and biochemical venom composition were also affected giving experimental evidence that the venom extraction not only causes tissue damage but also affects the composition stability and toxicity of the venom. In order to produce quality and effective antivenoms, an improvement of the management of snake collections could be established, such as rotation groups to assure the quality of the venom yielded.

Comprehensive Study of the Proteome and Transcriptome of the Venom of the Most Venomous European Viper: Discovery of a New Subclass of Ancestral Snake Venom Metalloproteinase Precursor-Derived Proteins

The nose-horned viper, its nominotypical subspecies Vipera ammodytes ammodytes (Vaa), in particular, is, medically, one of the most relevant snakes in Europe. The local and systemic clinical manifestations of poisoning by the venom of this snake are the result of the pathophysiological effects inflicted by enzymatic and nonenzymatic venom components acting, most prominently, on the blood, cardiovascular, and nerve systems. This venom is a very complex mixture of pharmacologically active proteins and peptides. To help improve the current antivenom therapy toward higher specificity and efficiency and to assist drug discovery, we have constructed, by combining transcriptomic and proteomic analyses, the most comprehensive library yet of the Vaa venom proteins and peptides. Sequence analysis of the venom gland cDNA library has revealed the presence of messages encoding 12 types of polypeptide precursors. The most abundant are those for metalloproteinase inhibitors (MPis), bradykinin-potentiating peptides (BPPs), and natriuretic peptides (NPs) (all three on a single precursor), snake C-type lectin-like proteins (snaclecs), serine proteases (SVSPs), P-II and P-III metalloproteinases (SVMPs), secreted phospholipases A₂ (sPLA₂s), and disintegrins (Dis). These constitute >88% of the venom transcriptome. At the protein level, 57 venom proteins belonging to 16 different protein families have been identified and, with SVSPs, sPLA₂s, snaclecs, and SVMPs, comprise ∼80% of all venom proteins. Peptides detected in the venom include NPs, BPPs, and inhibitors of SVSPs and SVMPs. Of particular interest, a transcript coding for a protein similar to P-III SVMPs but lacking the MP domain was also found at the protein level in the venom. The existence of such proteins, also supported by finding similar venom gland transcripts in related snake species, has been demonstrated for the first time, justifying the proposal of a new P-IIIe subclass of ancestral SVMP precursor-derived proteins.

Venom Composition in a Phenotypically Variable Pit Viper ( Trimeresurus insularis) across the Lesser Sunda Archipelago

The genus Trimeresurus comprises a group of venomous pitvipers endemic to Southeast Asia and the Pacific Islands. Of these, Trimeresurus insularis, the White-lipped Island Pitviper, is a nocturnal, arboreal species that occurs on nearly every major island of the Lesser Sunda archipelago. In the current study, venom phenotypic characteristics of T. insularis sampled from eight Lesser Sunda Islands (Flores, Lembata, Lombok, Pantar, Sumba, Sumbawa, Timor, and Wetar) were evaluated via SDS-PAGE, enzymatic activity assays, fibrinogenolytic assays, gelatin zymography, and RP-HPLC, and the Sumbawa sample was characterized by venomic analysis. For additional comparative analyses, venoms were also examined from several species in the Trimeresurus complex, including T. borneensis, T. gramineus, T. puniceus, T. purpureomaculatus, T. stejnegeri, and Protobothrops flavoviridis. Despite the geographical isolation, T. insularis venoms from all eight islands demonstrated remarkable similarities in gel electrophoretic profiles and RP-HPLC patterns, and all populations had protein bands in the mass ranges of phosphodiesterases (PDE), l-amino acid oxidases (LAAO), P-III snake venom metalloproteinases (SVMP), serine proteases, cysteine-rich secretory proteins (CRISP), phospholipases A₂ (PLA₂), and C-type lectins. An exception was observed in the Lombok sample, which lacked protein bands in the mass range of serine protease and CRISP. Venomic analysis of the Sumbawa venom also identified these protein families, in addition to several proteins of lesser abundance (<1%), including glutaminyl cyclase, aminopeptidase, PLA₂ inhibitor, phospholipase B, cobra venom factor, 5'-nucleotidase, vascular endothelial growth factor, and hyaluronidase. All T. insularis venoms exhibited similarities in thrombin-like and PDE activities, while significant differences were observed for LAAO, SVMP, and kallikrein-like activities, though these differences were only observed for a few islands. Slight but noticeable differences were also observed with fibrinogen and gelatin digestion activities. Trimeresurus insularis venoms exhibited overall similarity to the other Trimeresurus complex species examined, with the exception of P. flavoviridis venom, which showed the greatest overall differentiation. Western blot analysis revealed that all major T. insularis venom proteins were recognized by Green Pitviper ( T. albolabris) antivenom, and reactivity was also seen with most venom proteins of the other Trimeresurus species, but incomplete antivenom-venom recognition was observed against P. flavoviridis venom proteins. These results demonstrate significant conservation in the venom composition of T. insularis across the Lesser Sunda archipelago relative to the other Trimeresurus species examined.

Evidence for divergent patterns of local selection driving venom variation in Mojave Rattlesnakes (Crotalus scutulatus)

Snake venoms represent an enriched system for investigating the evolutionary processes that lead to complex and dynamic trophic adaptations. It has long been hypothesized that natural selection may drive geographic variation in venom composition, yet previous studies have lacked the population genetic context to examine these patterns. We leverage range-wide sampling of Mojave Rattlesnakes (Crotalus scutulatus) and use a combination of venom, morphological, phylogenetic, population genetic, and environmental data to characterize the striking dichotomy of neurotoxic (Type A) and hemorrhagic (Type B) venoms throughout the range of this species. We find that three of the four previously identified major lineages within C. scutulatus possess a combination of Type A, Type B, and a ‘mixed’ Type A + B venom phenotypes, and that fixation of the two main venom phenotypes occurs on a more fine geographic scale than previously appreciated. We also find that Type A + B individuals occur in regions of inferred introgression, and that this mixed phenotype is comparatively rare. Our results support strong directional local selection leading to fixation of alternative venom phenotypes on a fine geographic scale, and are inconsistent with balancing selection to maintain both phenotypes within a single population. Our comparisons to biotic and abiotic factors further indicate that venom phenotype correlates with fang morphology and climatic variables. We hypothesize that links to fang morphology may be indicative of co-evolution of venom and other trophic adaptations, and that climatic variables may be linked to prey distributions and/or physiology, which in turn impose selection pressures on snake venoms.

Organic and Peptidyl Constituents of Snake Venoms: The Picture Is Vastly More Complex Than We Imagined

Small metabolites and peptides in 17 snake venoms (Elapidae, Viperinae, and Crotalinae), were quantified using liquid chromatography-mass spectrometry. Each venom contains >900 metabolites and peptides. Many small organic compounds are present at levels that are probably significant in prey envenomation, given that their known pharmacologies are consistent with snake envenomation strategies. Metabolites included purine nucleosides and their bases, neurotransmitters, neuromodulators, guanidino compounds, carboxylic acids, amines, mono- and disaccharides, and amino acids. Peptides of 2⁻15 amino acids are also present in significant quantities, particularly in crotaline and viperine venoms. Some constituents are specific to individual taxa, while others are broadly distributed. Some of the latter appear to support high anabolic activity in the gland, rather than having toxic functions. Overall, the most abundant organic metabolite was citric acid, owing to its predominance in viperine and crotaline venoms, where it chelates divalent cations to prevent venom degradation by venom metalloproteases and damage to glandular tissue by phospholipases. However, in terms of their concentrations in individual venoms, adenosine, adenine, were most abundant, owing to their high titers in Dendroaspis polylepis venom, although hypoxanthine, guanosine, inosine, and guanine all numbered among the 50 most abundant organic constituents. A purine not previously reported in venoms, ethyl adenosine carboxylate, was discovered in D. polylepis venom, where it probably contributes to the profound hypotension caused by this venom. Acetylcholine was present in significant quantities only in this highly excitotoxic venom, while 4-guanidinobutyric acid and 5-guanidino-2-oxopentanoic acid were present in all venoms.

Venom Ontogeny in the Mexican Lance-Headed Rattlesnake (Crotalus polystictus)

As trophic adaptations, rattlesnake venoms can vary in composition depending on several intrinsic and extrinsic factors. Ontogenetic changes in venom composition have been documented for numerous species, but little is known of the potential age-related changes in many rattlesnake species found in México. In the current study, venom samples collected from adult and neonate Crotalus polystictus from Estado de México were subjected to enzymatic and electrophoretic analyses, toxicity assays (LD₅₀), and MALDI-TOF mass spectrometry, and a pooled sample of adult venom was analyzed by shotgun proteomics. Electrophoretic profiles of adult males and females were quite similar, and only minor sex-based variation was noted. However, distinct differences were observed between venoms from adult females and their neonate offspring. Several prominent bands, including P-I and P-III snake venom metalloproteinases (SVMPs) and disintegrins (confirmed by MS/MS) were present in adult venoms and absent/greatly reduced in neonate venoms. Age-dependent differences in SVMP, kallikrein-like, phospholipase A₂ (PLA₂), and L-amino acid oxidase (LAAO) activity levels were confirmed by enzymatic activity assays, and like many other rattlesnake species, venoms from adult snakes have higher SVMP activity than neonate venoms. Conversely, PLA₂ activity was approximately 2.5 × greater in venoms from neonates, likely contributing to the increased toxicity (neonate venom LD₅₀ = 4.5 μg/g) towards non-Swiss albino mice when compared to adult venoms (LD₅₀ = 5.5 μg/g). Thrombin-like (TLE) and phosphodiesterase activities did not vary significantly with age. A significant effect of sex (between adult male and adult female venoms) was also observed for SVMP, TLE, and LAAO activities. Analysis of pooled adult venom by LC-MS/MS identified 14 toxin protein families, dominated by bradykinin-inhibitory peptides, SVMPs (P-I, P-II and P-III), disintegrins, PLA₂s, C-type-lectins, CRiSPs, serine proteinases, and LAAOs (96% of total venom proteins). Neonate and adult C. polystictus in this population consume almost exclusively mammals, suggesting that age-based differences in composition are related to physical differences in prey (e.g., surface-to-volume ratio differences) rather than taxonomic differences between prey. Venoms from adult C. polystictus fit a Type I pattern (high SVMP activity, lower toxicity), which is characteristic of many larger-bodied rattlesnakes of North America.

Comparative Venomics of the Vipera ammodytes transcaucasiana and Vipera ammodytes montandoni from Turkey Provides Insights into Kinship

The Nose-horned Viper (Vipera ammodytes) is one of the most widespread and venomous snakes in Europe, which causes high frequent snakebite accidents. The first comprehensive venom characterization of the regional endemic Transcaucasian Nose-horned Viper (Vipera ammodytes transcaucasiana) and the Transdanubian Sand Viper (Vipera ammodytes montandoni) is reported employing a combination of intact mass profiling and bottom-up proteomics. The bottom-up analysis of both subspecies identified the major snake protein families of viper venoms. Furthermore, intact mass profiling revealed the presence of two tripeptidic metalloprotease inhibitors and their precursors. While previous reports applied multivariate analysis techniques to clarify the taxonomic status of the subspecies, an accurate classification of Vipera ammodytestranscaucasiana is still part of the ongoing research. The comparative analysis of the viper venoms on the proteome level reveals a close relationship between the Vipera ammodytes subspecies, which could be considered to clarify the classification of the Transcaucasian Nose-horned Viper. However, the slightly different ratio of some venom components could be indicating interspecific variations of the two studied subspecies or intraspecies alternations based on small sample size. Additionally, we performed a bioactivity screening with the crude venoms against several human cancerous and non-cancerous cell lines, which showed interesting results against a human breast adenocarcinoma epithelial cell line. Several fractions of Vipera a. transcaucasiana demonstrated a strong cytotoxic effect on triple negative MDA MB 231 breast cancer cells.

Biological and biochemical characterization of venom from the broad-banded copperhead (Agkistrodon contortrix laticinctus): isolation of two new dimeric disintegrins

Disintegrins represent a family of effective cell-cell and cell-matrix inhibitors by binding to integrin receptors. Integrins are heterodimeric, transmembrane receptors that are the bridges for these cell interactions. Disintegrins have been shown to have many therapeutic implications for the treatment of strokes, heart attacks, and cancer. Two novel heterodimeric disintegrins were isolated from the venom of the broad-banded copperhead (Agkistrodon contortrix laticinctus). Crude venom separated by cation-exchange chromatography resulted in several fractions possessing hemorrhagic, fibrinolytic, gelatinase, and platelet activities. Venom fractions 2-3 and 17-19 showed fibrinolytic activity. Fractions 2-6, 8-11, and 16-21 had hemorrhagic activity. Gelatinase activity was found in fractions 3, 11, and 19. The isolation of laticinstatins 1 and 2 was accomplished by fractionating crude venom using reverse phase chromatography. Data from both SDS-PAGE and N-terminal sequencing determined that laticinstatins 1 and 2 were heterodimeric disintegrins, and both were assayed for their ability to inhibit platelet aggregation in human whole blood. Future functional evaluation of snake venom disintegrins shows considerable promise for elucidating the biochemical mechanisms of integrin-ligand interactions that will allow the development of adequate medications for hemostatic pathologies such as thrombosis, stroke, and cerebral and cardiac accidents. In this study, we are presenting the first report of the purification, and partial characterization of two new dimeric disintegrins isolated from the venom of broad-banded copperhead snakes.

Snake Venom Metalloproteinases and Their Peptide Inhibitors from Myanmar Russell's Viper Venom

Russell's viper bites are potentially fatal from severe bleeding, renal failure and capillary leakage. Snake venom metalloproteinases (SVMPs) are attributed to these effects. In addition to specific antivenom therapy, endogenous inhibitors from snakes are of interest in studies of new treatment modalities for neutralization of the effect of toxins. Two major snake venom metalloproteinases (SVMPs): RVV-X and Daborhagin were purified from Myanmar Russell's viper venom using a new purification strategy. Using the Next Generation Sequencing (NGS) approach to explore the Myanmar RV venom gland transcriptome, mRNAs of novel tripeptide SVMP inhibitors (SVMPIs) were discovered. Two novel endogenous tripeptides, pERW and pEKW were identified and isolated from the crude venom. Both purified SVMPs showed caseinolytic activity. Additionally, RVV-X displayed specific proteolytic activity towards gelatin and Daborhagin showed potent fibrinogenolytic activity. These activities were inhibited by metal chelators. Notably, the synthetic peptide inhibitors, pERW and pEKW, completely inhibit the gelatinolytic and fibrinogenolytic activities of respective SVMPs at 5 mM concentration. These complete inhibitory effects suggest that these tripeptides deserve further study for development of a therapeutic candidate for Russell's viper envenomation.

Proteomic analysis of venom variability and ontogeny across the arboreal palm-pitvipers (genus Bothriechis)

Bothriechis is a genus of eleven currently recognized slender and arboreal venomous snakes, commonly called palm-pitvipers that range from southern Mexico to northern South America. Despite dietary studies suggesting that palm-pitvipers are generalists with an ontogenetic shift toward endothermic prey, venom proteomic analyses have revealed remarkable divergence between the venoms of the Costa Rican species, B. lateralis, B. schlegelii, B. supraciliaris, and B. nigroviridis. To achieve a more complete picture of the venomic landscape across Bothriechis, the venom proteomes of biodiversity of the northern Middle American highland palm-pitvipers, B. thalassinus, B. aurifer, and B. bicolor from Guatemala, B. marchi from Honduras, and neonate Costa Rican B. lateralis and B. schlegelii, were investigated. B. thalassinus and B. aurifer venoms are comprised by similar toxin arsenals dominated by SVMPs (33-39% of the venom proteome), CTLs (11-16%), BPP-like molecules (10-13%), and CRISPs (5-10%), and are characterized by the absence of PLA₂ proteins. Conversely, the predominant (35%) components of B. bicolor are D49-PLA₂ molecules. The venom proteome of B. marchi is similar to B. aurifer and B. thalassinus in that it is rich in SVMPs and BPPs, but also contains appreciable amounts (14.3%) of PLA₂s. The major toxin family found in the venoms of both neonate B. lateralis and B. schlegelii, is serine proteinase (SVSP), comprising about 20% of their toxin arsenals. The venom of neonate B. schlegelii is the only palm-pitviper venom where relative high amounts of Kunitz-type (6.3%) and γPLA₂ (5.2%) inhibitors have been identified. Despite notable differences between their proteomes, neonate venoms are more similar to each other than to adults of their respective species. However, the ontogenetic changes taking place in the venom of B. lateralis strongly differ from those that occur in the venom of B. schlegelii. Thus, the ontogenetic change in B. lateralis produces a SVMP-rich venom, whereas in B. schlegelii the age-dependent compositional shift generates a PLA₂-rich venom. Overall, genus-wide venomics illustrate the high evolvability of palm-pitviper venoms. The integration of the pattern of venom variation across Bothriechis into a phylogenetic and biogeographic framework may lay the foundation for assessing, in future studies, the evolutionary path that led to the present-day variability of the venoms of palm-pitvipers.

SIGNIFICANCE

Bothriechis represents a monophyletic basal genus of eleven arboreal palm-pitvipers that range from southern Mexico to northern South America. Despite palm-pitvipers' putative status as diet generalists, previous proteomic analyses have revealed remarkable divergence between the venoms of Costa Rican species, B. lateralis, B. schlegelii, B. supraciliaris, and B. nigroviridis. Our current proteomic study of Guatemalan species, B. thalassinus, B. aurifer, and B. bicolor, Honduran B. marchi, and neonate B. lateralis and B. schlegelii from Costa Rica was undertaken to deepen our understanding of the evolutionary pattern of venom proteome diversity across Bothriechis. Ancestral characters are often, but not always, preserved in an organism's development. Venoms of neonate B. lateralis and B. schlegelii are more similar to each other than to adults of their respective species, suggesting that the high evolvability of palm-pitviper venoms may represent an inherent feature of Bothriechis common ancestor. Our genus-wide data identified four nodes of venom phenotype differentiation across the phylogeny of Bothriechis. Integrated into a phylogenetic and biogeographic framework, the pattern of venom variation across Bothriechis may lay the groundwork to establish whether divergence was driven by selection for efficient resource exploitation in arboreal 'islands', thereby contributing to the ecological speciation of the genus.

Colubrid Venom Composition: An -Omics Perspective

Snake venoms have been subjected to increasingly sensitive analyses for well over 100 years, but most research has been restricted to front-fanged snakes, which actually represent a relatively small proportion of extant species of advanced snakes. Because rear-fanged snakes are a diverse and distinct radiation of the advanced snakes, understanding venom composition among "colubrids" is critical to understanding the evolution of venom among snakes. Here we review the state of knowledge concerning rear-fanged snake venom composition, emphasizing those toxins for which protein or transcript sequences are available. We have also added new transcriptome-based data on venoms of three species of rear-fanged snakes. Based on this compilation, it is apparent that several components, including cysteine-rich secretory proteins (CRiSPs), C-type lectins (CTLs), CTLs-like proteins and snake venom metalloproteinases (SVMPs), are broadly distributed among "colubrid" venoms, while others, notably three-finger toxins (3FTxs), appear nearly restricted to the Colubridae (sensu stricto). Some putative new toxins, such as snake venom matrix metalloproteinases, are in fact present in several colubrid venoms, while others are only transcribed, at lower levels. This work provides insights into the evolution of these toxin classes, but because only a small number of species have been explored, generalizations are still rather limited. It is likely that new venom protein families await discovery, particularly among those species with highly specialized diets.

Processing of Snake Venom Metalloproteinases: Generation of Toxin Diversity and Enzyme Inactivation

Snake venom metalloproteinases (SVMPs) are abundant in the venoms of vipers and rattlesnakes, playing important roles for the snake adaptation to different environments, and are related to most of the pathological effects of these venoms in human victims. The effectiveness of SVMPs is greatly due to their functional diversity, targeting important physiological proteins or receptors in different tissues and in the coagulation system. Functional diversity is often related to the genetic diversification of the snake venom. In this review, we discuss some published evidence that posit that processing and post-translational modifications are great contributors for the generation of functional diversity and for maintaining latency or inactivation of enzymes belonging to this relevant family of venom toxins.

Mass spectrometry guided venom profiling and bioactivity screening of the Anatolian Meadow Viper, Vipera anatolica

This contribution reports on the first characterization of the venom proteome and the bioactivity screening of Vipera anatolica, the Anatolian Meadow Viper. The crude venom as well as an isolated dimeric disintegrin showed remarkable cytotoxic activity against glioblastoma cells. Due to the rare occurrence and the small size of this species only little amount of venom was available, which was profiled by means of a combination of bottom-up and top-down mass spectrometry. From this analysis we identified snake venom metalloproteases, cysteine-rich secretory protein isoforms, a metalloprotease inhibitor, several type A2 phospholipases, disintegrins, a snake venom serine protease, a C-type lectin and a Kunitz-type protease inhibitor. Furthermore, we detected several isoforms of above mentioned proteins as well as previously unknown proteins, indicating an extensive complexity of the venom which would have remained undetected with conventional venomic approaches.

Crystal structure of a Trimeresurus mucrosquamatus venom metalloproteinase providing new insights into the inhibition by endogenous tripeptide inhibitors

The crystal structure of TM-1, a P-I class snake-venom metalloproteinase (SVMP) from the Trimeresurus mucrosquamatus venom, was determined at 1.8-Å resolution. The structure exhibits the typical feature of SVMPs and is stabilized by three disulfide linkages. The active site shows a deep S1' substrate-binding pocket limited by the non-conserved Pro174 at the bottom. Further comparisons with other SVMPs suggest that the deep S1' site of TM-1 correlates with its high inhibition sensitivity to the endogenous tripeptide inhibitors. Proteolytic specificity analysis revealed that TM-1 prefers substrates having a moderate-size and hydrophobic residue at the P1' position, consistent with our structural observation.

Profiling the venom gland transcriptomes of Costa Rican snakes by 454 pyrosequencing

BACKGROUND

A long term research goal of venomics, of applied importance for improving current antivenom therapy, but also for drug discovery, is to understand the pharmacological potential of venoms. Individually or combined, proteomic and transcriptomic studies have demonstrated their feasibility to explore in depth the molecular diversity of venoms. In the absence of genome sequence, transcriptomes represent also valuable searchable databases for proteomic projects.

RESULTS

The venom gland transcriptomes of 8 Costa Rican taxa from 5 genera (Crotalus, Bothrops, Atropoides, Cerrophidion, and Bothriechis) of pitvipers were investigated using high-throughput 454 pyrosequencing. 100,394 out of 330,010 masked reads produced significant hits in the available databases. 5.165,220 nucleotides (8.27%) were masked by RepeatMasker, the vast majority of which corresponding to class I (retroelements) and class II (DNA transposons) mobile elements. BLAST hits included 79,991 matches to entries of the taxonomic suborder Serpentes, of which 62,433 displayed similarity to documented venom proteins. Strong discrepancies between the transcriptome-computed and the proteome-gathered toxin compositions were obvious at first sight. Although the reasons underlaying this discrepancy are elusive, since no clear trend within or between species is apparent, the data indicate that individual mRNA species may be translationally controlled in a species-dependent manner. The minimum number of genes from each toxin family transcribed into the venom gland transcriptome of each species was calculated from multiple alignments of reads matched to a full-length reference sequence of each toxin family. Reads encoding ORF regions of Kazal-type inhibitor-like proteins were uniquely found in Bothriechis schlegelii and B. lateralis transcriptomes, suggesting a genus-specific recruitment event during the early-Middle Miocene. A transcriptome-based cladogram supports the large divergence between A. mexicanus and A. picadoi, and a closer kinship between A. mexicanus and C. godmani.

CONCLUSIONS

Our comparative next-generation sequencing (NGS) analysis reveals taxon-specific trends governing the formulation of the venom arsenal. Knowledge of the venom proteome provides hints on the translation efficiency of toxin-coding transcripts, contributing thereby to a more accurate interpretation of the transcriptome. The application of NGS to the analysis of snake venom transcriptomes, may represent the tool for opening the door to systems venomics.

Autolysis at the disintegrin domain of patagonfibrase, a metalloproteinase from Philodryas patagoniensis (Patagonia Green Racer; Dipsadidae) venom

Patagonfibrase is a 57.5-kDa hemorrhagic metalloproteinase isolated from the venom of Philodryas patagoniensis (Patagonia Green Racer), a South American rear-fanged snake. Herein we demonstrate that patagonfibrase undergoes autolysis at its pH optimum (7.5) and at 37 degrees C, primarily producing a approximately 32.6 kDa fragment composed of disintegrin-like and cysteine-rich domains, as identified by mass spectrometry and N-terminal sequencing. The autolysis site for production of this fragment is similar to that observed for metalloproteinases from front-fanged Viperidae snake venoms. In the presence of Ca(2+), patagonfibrase was only partially autolysed, giving rise mainly to one fragment of approximately 52.2 kDa. In addition, calcium markedly enhanced the azocaseinolytic activity of patagonfibrase. Our findings contribute to the understanding of the structural and mechanistic bases of this family of metalloenzymes that are widely distributed among snake venoms, demonstrating that important post-translational modifications such as proteolysis can also contribute to the diversity and complexity of proteins found in rear-fanged snake venoms.

Sensationalistic journalism and tales of snakebite: are rattlesnakes rapidly evolving more toxic venom?

Recent reports in the lay press have suggested that bites by rattlesnakes in the last several years have been more severe than those in the past. The explanation, often citing physicians, is that rattlesnakes are evolving more toxic venom, perhaps in response to anthropogenic causes. We suggest that other explanations are more parsimonious, including factors dependent on the snake and factors associated with the bite victim's response to envenomation. Although bites could become more severe from an increased proportion of bites from larger or more provoked snakes (ie, more venom injected), the venom itself evolves much too slowly to explain the severe symptoms occasionally seen. Increased snakebite severity could also result from a number of demographic changes in the victim profile, including age and body size, behavior toward the snake (provocation), anatomical site of bite, clothing, and general health including asthma prevalence and sensitivity to foreign antigens. Clinical management of bites also changes perpetually, rendering comparisons of snakebite severity over time tenuous. Clearly, careful study taking into consideration many factors will be essential to document temporal changes in snakebite severity or venom toxicity. Presently, no published evidence for these changes exists. The sensationalistic coverage of these atypical bites and accompanying speculation is highly misleading and can produce many detrimental results, such as inappropriate fear of the outdoors and snakes, and distraction from proven snakebite management needs, including a consistent supply of antivenom, adequate health care, and training. We urge healthcare providers to avoid propagating misinformation about snakes and snakebites.

Exploring the venom proteome of the western diamondback rattlesnake, Crotalus atrox, via snake venomics and combinatorial peptide ligand library approaches

We report the proteomic characterization of the venom of the medically important North American western diamondback rattlesnake, Crotalus atrox, using two complementary approaches: snake venomics (to gain an insight of the overall venom proteome), and two solid-phase combinatorial peptide ligand libraries (CPLL), followed by 2D electrophoresis and mass spectrometric characterization of in-gel digested protein bands (to capture and "amplify" low-abundance proteins). The venomics approach revealed approximately 24 distinct proteins belonging to 2 major protein families (snake venom metalloproteinases, SVMP, and serine proteinases), which represent 69.5% of the total venom proteins, 4 medium abundance families (medium-size disintegrin, PLA(2), cysteine-rich secretory protein, and l-amino acid oxidase) amounting to 25.8% of the venom proteins, and 3 minor protein families (vasoactive peptides, endogenous inhibitor of SVMP, and C-type lectin-like). This toxin profile potentially explains the cytotoxic, myotoxic, hemotoxic, and hemorrhagic effects evoked by C. atrox envenomation. Further, our results showing that C. atrox exhibits a similar level of venom variation as Sistrurus miliarius points to a "diversity gain" scenario in the lineage leading to the Sistrurus catenatus taxa. On the other hand, the two combinatorial hexapeptide libraries captured distinct sets of proteins. Although the CPLL-treated samples did not retain a representative venom proteome, protein spots barely, or not at all, detectable in the whole venom were enriched in the two CPLL-treated samples. The amplified low copy number C. atrox venom proteins comprised a C-type lectin-like protein, several PLA(2) molecules, PIII-SVMP isoforms, glutaminyl cyclase isoforms, and a 2-cys peroxiredoxin highly conserved across the animal kingdom. Peroxiredoxin and glutaminyl cyclase may participate, respectively, in redox processes leading to the structural/functional diversification of toxins, and in the N-terminal pyrrolidone carboxylic acid formation required in the maturation of bioactive peptides such as bradykinin-potentiating peptides and endogenous inhibitors of metalloproteases. Our findings underscore the usefulness of combinatorial peptide libraries as powerful tools for mining below the tip of the iceberg, complementing thereby the data gained using the snake venomics protocol toward a complete visualization of the venom proteome.

Self-proteolysis regulation in the Bothrops jararaca venom: the metallopeptidases and their intrinsic peptidic inhibitor

Snake venom proteome variation is a well-documented phenomenon, whereas peptidome variation is still relatively unknown. We used a biological approach to explore the inhibitory activities present in the whole venom of Bothrops jararaca that prevents the venom self-proteolysis and/or digestion of the glandular tissue. Although snake venom metallopeptidases have long been known from the biochemical up to the clinical point of view, the mechanisms by which these enzymes are regulated in the reptile's venom gland remain fairly unknown. We have successfully demonstrated that there are three synergistic weak inhibitory mechanisms that are present in the crude venom that are able to abolish the metallopeptidase activity in situ, namely: (i) citrate calcium chelation; (ii) acidic pH and; (iii) enzymatic competitive inhibition by the tripeptide Pyroglutamyl-lysyl-tryptophan. Taken together, these three factors become a strong set-up that inhibits the crude venom metallopeptidase activity as well as a purified metallopeptidase from this same venom. However, this inhibition can be totally reverted by dilution into an optimal pH solution, such as the blood.

Peptide fingerprinting of snake venoms by direct infusion nano-electrospray ionization mass spectrometry: potential use in venom identification and taxonomy

Fingerprinting by mass spectrometry has been increasingly used to study venom variations and for taxonomic analyses based on venom components. Most of these studies have concentrated on components heavier than 3 kDa, but Bothrops snake venoms contain many biologically active peptides, principally C-type natriuretic peptides and bradykinin-potentiating peptides (BPPs). In this work, we have examined the peptide profile of Bothrops venoms (B. alternatus, B. erythromelas, B. insularis, B. jararaca, B. jararacussu, B. leucurus and B. moojeni) using direct infusion nano-electrospray ionization mass spectrometry (nano-ESI-MS) subjecting the data further to principal components analysis (PCA) to assess whether the peptide distributions are reliable in distinguishing the venoms. ESI-MS of a low molar mass fraction obtained by ultrafiltration of each venom (5 kDa nominal cutoff filters) revealed that the venoms have a variety of peptides in common but that each venom also contains taxonomic marker peptides not shared with other venoms. One BPP peptide, QGGWPRPGPEIPP, was found to be common to the seven Bothrops species examined. This peptide may represent a specific marker for this genus since it was not found in the venom of the South American rattlesnake, Crotalus durissus terrificus. PCA on the ESI-MS data reveals a close relationship between B. jararaca, B. jararacussu and B. moojeni venoms, with B. leucurus and B. erythromelas being more distant from these three; B. alternatus and B. insularis were also located distant from these five species, as was C. d. terrificus. These results agree partially with established phylogenetic relationships among these species and suggest that ESI-MS peptide fingerprinting of snake venoms coupled with PCA is a useful tool for identifying venoms and for taxonomic analyses.

Microvesicles in the venom of Crotalus durissus terrificus (Serpentes, Viperidae)

Microvesicles with electron-dense content are consistently observed by transmission electron microscopy on the luminal face of secretory cells of venom glands of viperid snakes. In this work, we evaluated their presence in Crotalus durissus terrificus venom glands and also in freshly collected venom. Microvesicles were found in the venom glands mainly in regions of exocytosis. They ranged from 40 to 80 nm in diameter. Freeze-fracture replicas of the glands revealed particles on the cytoplasmic leaflet (P-face) of these vesicles, suggesting that they carry transmembrane proteins. Vesicles separated by ultracentrifugation from cell-free venom were similar in size and structure to the microvesicles observed in the glands. A fine fuzzy coat surrounded each microvesicle. The function of these venom vesicles is still unknown, but they may contribute to inactivation of stored venom components, or their activation after the venom is released.

Crystal structure of a non-hemorrhagic fibrin(ogen)olytic metalloproteinase complexed with a novel natural tri-peptide inhibitor from venom of Agkistrodon acutus

Thrombotic occlusive diseases pose a great threat to human health. Thrombolytic agents are in widespread use for the dissolution of arterial and venous pathologic thrombi in these kinds of diseases. Snake venom metalloproteinases (SVMPs) can act directly on fibrin/fibrinogen and are therefore potential candidates for therapeutic use against thrombotic occlusive diseases. In this study, we have determined the crystal structure of FII, a novel non-hemorrhagic SVMP isolated from Anhui Agkistrodon acutus snake venom by molecular replacement. The structure reveals that FII is a member of the P-I class SVMPs. The Zn2+ ion essential for hydrolytic activity is found in the active site and is tetrahedrally co-ordinated by three histidine residues and water molecule. Unambiguous electron density for a tri-peptide with sequence KNL is also found located near the active site. Biochemical evidences show that the tri-peptide KNL can inhibit the enzymatic activity of FII.