High-Voltage Toxin'Roll: Electrostatic Charge Repulsion as a Dynamic Venom Resistance Trait in Pythonid Snakes

The evolutionary interplay between predator and prey has significantly shaped the development of snake venom, a critical adaptation for subduing prey. This arms race has spurred the diversification of the components of venom and the corresponding emergence of resistance mechanisms in the prey and predators of venomous snakes. Our study investigates the molecular basis of venom resistance in pythons, focusing on electrostatic charge repulsion as a defense against α-neurotoxins binding to the alpha-1 subunit of the postsynaptic nicotinic acetylcholine receptor. Through phylogenetic and bioactivity analyses of orthosteric site sequences from various python species, we explore the prevalence and evolution of amino acid substitutions that confer resistance by electrostatic repulsion, which initially evolved in response to predatory pressure by Naja (cobra) species (which occurs across Africa and Asia). The small African species Python regius retains the two resistance-conferring lysines (positions 189 and 191) of the ancestral Python genus, conferring resistance to sympatric Naja venoms. This differed from the giant African species Python sebae, which has secondarily lost one of these lysines, potentially due to its rapid growth out of the prey size range of sympatric Naja species. In contrast, the two Asian species Python brongersmai (small) and Python bivittatus (giant) share an identical orthosteric site, which exhibits the highest degree of resistance, attributed to three lysine residues in the orthosteric sites. One of these lysines (at orthosteric position 195) evolved in the last common ancestor of these two species, which may reflect an adaptive response to increased predation pressures from the sympatric α-neurotoxic snake-eating genus Ophiophagus (King Cobras) in Asia. All these terrestrial Python species, however, were less neurotoxin-susceptible than pythons in other genera which have evolved under different predatory pressure as: the Asian species Malayopython reticulatus which is arboreal as neonates and juveniles before rapidly reaching sizes as terrestrial adults too large for sympatric Ophiophagus species to consider as prey; and the terrestrial Australian species Aspidites melanocephalus which occupies a niche, devoid of selection pressure from α-neurotoxic predatory snakes. Our findings underline the importance of positive selection in the evolution of venom resistance and suggest a complex evolutionary history involving both conserved traits and secondary evolution. This study enhances our understanding of the molecular adaptations that enable pythons to survive in environments laden with venomous threats and offers insights into the ongoing co-evolution between venomous snakes and their prey.

Distinct regulatory networks control toxin gene expression in elapid and viperid snakes

BACKGROUND

Venom systems are ideal models to study genetic regulatory mechanisms that underpin evolutionary novelty. Snake venom glands are thought to share a common origin, but there are major distinctions between venom toxins from the medically significant snake families Elapidae and Viperidae, and toxin gene regulatory investigations in elapid snakes have been limited. Here, we used high-throughput RNA-sequencing to profile gene expression and microRNAs between active (milked) and resting (unmilked) venom glands in an elapid (Eastern Brown Snake, Pseudonaja textilis), in addition to comparative genomics, to identify cis- and trans-acting regulation of venom production in an elapid in comparison to viperids (Crotalus viridis and C. tigris).

RESULTS

Although there is conservation in high-level mechanistic pathways regulating venom production (unfolded protein response, Notch signaling and cholesterol homeostasis), there are differences in the regulation of histone methylation enzymes, transcription factors, and microRNAs in venom glands from these two snake families. Histone methyltransferases and transcription factor (TF) specificity protein 1 (Sp1) were highly upregulated in the milked elapid venom gland in comparison to the viperids, whereas nuclear factor I (NFI) TFs were upregulated after viperid venom milking. Sp1 and NFI cis-regulatory elements were common to toxin gene promoter regions, but many unique elements were also present between elapid and viperid toxins. The presence of Sp1 binding sites across multiple elapid toxin gene promoter regions that have been experimentally determined to regulate expression, in addition to upregulation of Sp1 after venom milking, suggests this transcription factor is involved in elapid toxin expression. microRNA profiles were distinctive between milked and unmilked venom glands for both snake families, and microRNAs were predicted to target a diversity of toxin transcripts in the elapid P. textilis venom gland, but only snake venom metalloproteinase transcripts in the viperid C. viridis venom gland. These results suggest differences in toxin gene posttranscriptional regulation between the elapid P. textilis and viperid C. viridis.

CONCLUSIONS

Our comparative transcriptomic and genomic analyses between toxin genes and isoforms in elapid and viperid snakes suggests independent toxin regulation between these two snake families, demonstrating multiple different regulatory mechanisms underpin a venomous phenotype.

The roles of balancing selection and recombination in the evolution of rattlesnake venom

The origin of snake venom involved duplication and recruitment of non-venom genes into venom systems. Several studies have predicted that directional positive selection has governed this process. Venom composition varies substantially across snake species and venom phenotypes are locally adapted to prey, leading to coevolutionary interactions between predator and prey. Venom origins and contemporary snake venom evolution may therefore be driven by fundamentally different selection regimes, yet investigations of population-level patterns of selection have been limited. Here, we use whole-genome data from 68 rattlesnakes to test hypotheses about the factors that drive genomic diversity and differentiation in major venom gene regions. We show that selection has resulted in long-term maintenance of genetic diversity within and between species in multiple venom gene families. Our findings are inconsistent with a dominant role of directional positive selection and instead support a role of long-term balancing selection in shaping venom evolution. We also detect rapid decay of linkage disequilibrium due to high recombination rates in venom regions, suggesting that venom genes have reduced selective interference with nearby loci, including other venom paralogues. Our results provide an example of long-term balancing selection that drives trans-species polymorphism and help to explain how snake venom keeps pace with prey resistance.

Contextual Constraints: Dynamic Evolution of Snake Venom Phospholipase A2

Venom is a dynamic trait that has contributed to the success of numerous organismal lineages. Predominantly composed of proteins, these complex cocktails are deployed for predation and/or self-defence. Many non-toxic physiological proteins have been convergently and recurrently recruited by venomous animals into their toxin arsenal. Phospholipase A₂ (PLA₂) is one such protein and features in the venoms of many organisms across the animal kingdom, including snakes of the families Elapidae and Viperidae. Understanding the evolutionary history of this superfamily would therefore provide insight into the origin and diversification of venom toxins and the evolution of novelty more broadly. The literature is replete with studies that have identified diversifying selection as the sole influence on PLA₂ evolution. However, these studies have largely neglected the structural/functional constraints on PLA₂s, and the ecology and evolutionary histories of the diverse snake lineages that produce them. By considering these crucial factors and employing evolutionary analyses integrated with a schema for the classification of PLA₂s, we uncovered lineage-specific differences in selection regimes. Thus, our work provides novel insights into the evolution of this major snake venom toxin superfamily and underscores the importance of considering the influence of evolutionary and ecological contexts on molecular evolution.

Tracking the recruitment and evolution of snake toxins using the evolutionary context provided by the Bothrops jararaca genome

Venom is a key adaptive innovation in snakes, and how nonvenom genes were co-opted to become part of the toxin arsenal is a significant evolutionary question. While this process has been investigated through the phylogenetic reconstruction of toxin sequences, evidence provided by the genomic context of toxin genes remains less explored. To investigate the process of toxin recruitment, we sequenced the genome of Bothrops jararaca, a clinically relevant pitviper. In addition to producing a road map with canonical structures of genes encoding 12 toxin families, we inferred most of the ancestral genes for their loci. We found evidence that 1) snake venom metalloproteinases (SVMPs) and phospholipases A2 (PLA2) have expanded in genomic proximity to their nonvenomous ancestors; 2) serine proteinases arose by co-opting a local gene that also gave rise to lizard gilatoxins and then expanded; 3) the bradykinin-potentiating peptides originated from a C-type natriuretic peptide gene backbone; and 4) VEGF-F was co-opted from a PGF-like gene and not from VEGF-A. We evaluated two scenarios for the original recruitment of nontoxin genes for snake venom: 1) in locus ancestral gene duplication and 2) in locus ancestral gene direct co-option. The first explains the origins of two important toxins (SVMP and PLA2), while the second explains the emergence of a greater number of venom components. Overall, our results support the idea of a locally assembled venom arsenal in which the most clinically relevant toxin families expanded through posterior gene duplications, regardless of whether they originated by duplication or gene co-option.

Phylogenetically diverse diets favor more complex venoms in North American pitvipers

The role of natural selection in the evolution of trait complexity can be characterized by testing hypothesized links between complex forms and their functions across species. Predatory venoms are composed of multiple proteins that collectively function to incapacitate prey. Venom complexity fluctuates over evolutionary timescales, with apparent increases and decreases in complexity, and yet the causes of this variation are unclear. We tested alternative hypotheses linking venom complexity and ecological sources of selection from diet in the largest clade of front-fanged venomous snakes in North America: the rattlesnakes, copperheads, cantils, and cottonmouths. We generated independent transcriptomic and proteomic measures of venom complexity and collated several natural history studies to quantify dietary variation. We then constructed genome-scale phylogenies for these snakes for comparative analyses. Strikingly, prey phylogenetic diversity was more strongly correlated to venom complexity than was overall prey species diversity, specifically implicating prey species' divergence, rather than the number of lineages alone, in the evolution of complexity. Prey phylogenetic diversity further predicted transcriptomic complexity of three of the four largest gene families in viper venom, showing that complexity evolution is a concerted response among many independent gene families. We suggest that the phylogenetic diversity of prey measures functionally relevant divergence in the targets of venom, a claim supported by sequence diversity in the coagulation cascade targets of venom. Our results support the general concept that the diversity of species in an ecological community is more important than their overall number in determining evolutionary patterns in predator trait complexity.

ToxCodAn: a new toxin annotator and guide to venom gland transcriptomics

MOTIVATION

Next-generation sequencing has become exceedingly common and has transformed our ability to explore nonmodel systems. In particular, transcriptomics has facilitated the study of venom and evolution of toxins in venomous lineages; however, many challenges remain. Primarily, annotation of toxins in the transcriptome is a laborious and time-consuming task. Current annotation software often fails to predict the correct coding sequence and overestimates the number of toxins present in the transcriptome. Here, we present ToxCodAn, a python script designed to perform precise annotation of snake venom gland transcriptomes. We test ToxCodAn with a set of previously curated transcriptomes and compare the results to other annotators. In addition, we provide a guide for venom gland transcriptomics to facilitate future research and use Bothrops alternatus as a case study for ToxCodAn and our guide.

RESULTS

Our analysis reveals that ToxCodAn provides precise annotation of toxins present in the transcriptome of venom glands of snakes. Comparison with other annotators demonstrates that ToxCodAn has better performance with regard to run time ($>20x$ faster), coding sequence prediction ($>3x$ more accurate) and the number of toxins predicted (generating $>4x$ less false positives). In this sense, ToxCodAn is a valuable resource for toxin annotation. The ToxCodAn framework can be expanded in the future to work with other venomous lineages and detect novel toxins.

Antithrombotic and anticoagulant effects of a novel protein isolated from the venom of the Deinagkistrodon acutus snake

The venom of the Deinagkistrodon acutus snake is composed of numerous bioactive proteins and peptides. In this study, we report the antithrombotic and anticoagulant activities of one of such proteins, herein known as SLPC. This novel protein was isolated and purified via multi-gel chromatography. Its amino acid sequence, structure and function were then determined. This protein was found to exhibit defibration, anticoagulation and general antithrombotic effects based on the results of both in vitro and in vivo studies. Based on same studies, it was found to cleave the α, β, γ chains of fibrinogen and generally improved antiplatelet aggregation and blood rheology. A metabolomic insight of the antithrombotic effects of SLPC was found to be mainly linked to perturbations in the synthesis of unsaturated fatty acids, glycerophospholipid metabolism, arachidonic acid metabolism and other metabolic pathways. In summary, the novel protein SLPC, elicits its antithrombotic effects via degradation of fibrinogen and regulation of various thrombogenic factors in multiple metabolic pathways.

Replacement and Parallel Simplification of Nonhomologous Proteinases Maintain Venom Phenotypes in Rear-Fanged Snakes

Novel phenotypes are commonly associated with gene duplications and neofunctionalization, less documented are the cases of phenotypic maintenance through the recruitment of novel genes. Proteolysis is the primary toxic character of many snake venoms, and ADAM metalloproteinases, named snake venom metalloproteinases (SVMPs), are largely recognized as the major effectors of this phenotype. However, by investigating original transcriptomes from 58 species of advanced snakes (Caenophidia) across their phylogeny, we discovered that a different enzyme, matrix metalloproteinase (MMP), is actually the dominant venom component in three tribes (Tachymenini, Xenodontini, and Conophiini) of rear-fanged snakes (Dipsadidae). Proteomic and functional analyses of these venoms further indicate that MMPs are likely playing an "SVMP-like" function in the proteolytic phenotype. A detailed look into the venom-specific sequences revealed a new highly expressed MMP subtype, named snake venom MMP (svMMP), which originated independently on at least three occasions from an endogenous MMP-9. We further show that by losing ancillary noncatalytic domains present in its ancestors, svMMPs followed an evolutionary path toward a simplified structure during their expansion in the genomes, thus paralleling what has been proposed for the evolution of their Viperidae counterparts, the SVMPs. Moreover, we inferred an inverse relationship between the expression of svMMPs and SVMPs along the evolutionary history of Xenodontinae, pointing out that one type of enzyme may be substituting for the other, whereas the general (metallo)proteolytic phenotype is maintained. These results provide rare evidence on how relevant phenotypic traits can be optimized via natural selection on nonhomologous genes, yielding alternate biochemical components.

Cysteine-Rich Secretory Proteins (CRISPs) From Venomous Snakes: An Overview of the Functional Diversity in A Large and Underappreciated Superfamily

The CAP protein superfamily (Cysteine-rich secretory proteins (CRISPs), Antigen 5 (Ag5), and Pathogenesis-related 1 (PR-1) proteins) is widely distributed, but for toxinologists, snake venom CRISPs are the most familiar members. Although CRISPs are found in the majority of venoms, very few of these proteins have been functionally characterized, but those that have been exhibit diverse activities. Snake venom CRISPs (svCRISPs) inhibit ion channels and the growth of new blood vessels (angiogenesis). They also increase vascular permeability and promote inflammatory responses (leukocyte and neutrophil infiltration). Interestingly, CRISPs in lamprey buccal gland secretions also manifest some of these activities, suggesting an evolutionarily conserved function. As we strive to better understand the functions that CRISPs serve in venoms, it is worth considering the broad range of CRISP physiological activities throughout the animal kingdom. In this review, we summarize those activities, known crystal structures and sequence alignments, and we discuss predicted functional sites. CRISPs may not be lethal or major components of venoms, but given their almost ubiquitous occurrence in venoms and the accelerated evolution of svCRISP genes, these venom proteins are likely to have functions worth investigating.

Philodryas (Serpentes: Dipsadidae) Envenomation, a Neglected Issue in Chile

Snakebite envenomation is considered a neglected tropical disease, although it also occurs outside the tropics. In this work, we analyzed the literature on Philodryas species in Chile (Philodryaschamissonis, P.simonsii, and P.tachymenoides) from 1834 to 2019, searching for epidemiological, clinical, and molecular aspects of envenomation. Ninety-one percent of the studies found regarded taxonomy, ecology, and natural history, suggesting that snakebites and venom toxins are a neglected issue in Chile. All snakebite cases reported and toxicological studies concerned the species Philodryaschamissonis. Using 185 distributional records from the literature and museum collections for this species, we show for the first time that the reported snakebite cases correlate with human population density, occurring in the Valparaiso and Metropolitan regions in Central Chile. The reduced number of snakebite cases, which were previously considered as having a low incidence in Chile, may be a consequence of under-reported cases, probably due to the inadequate publication or scarce research on this issue. Absence of information about official pharmacological treatment, post-envenoming sequels, clinical management of particular patient groups (e.g., with non-communicable diseases, pregnant women, and the elderly) was also detected. In conclusion, despite having over 185 years of literature on Chilean snakes, knowledge on the envenomation of Philodryas genus remains scarce, seriously affecting adequate medical handling during an ophidic accident. This review highlights the need to develop deep research in this area and urgent improvements to the management of this disease in Chile.

Comparative compositional and functional analyses of Bothrops moojeni specimens reveal several individual variations

Snake venoms are complex protein mixtures with different biological activities that can act in both their preys and human victims. Many of these proteins play a role in prey capture and in the digestive process of these animals. It is known that some snakes are resistant to the toxicity of their own venom by mechanisms not yet fully elucidated. However, it was observed in the Laboratory of Herpetology of Instituto Butantan that some Bothrops moojeni individuals injured by the same snake species showed mortalities caused by envenoming effects. This study analyzed the biochemical composition of 13 venom and plasma samples from Bothrops moojeni specimens to assess differences in their protein composition. Application of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed distinct venom protein profiles, but very homogeneous plasma profiles. Western Blotting (WB) was performed with plasma samples, which were submitted to incubation with the respective venom. Some individuals showed an immunorecognized band zone around 25 kDa, indicating interaction between the same individual plasma and venom proteins. Crossed-WB assay using non-self-plasma and venom showed that this variability is due to venom protein composition instead of plasma composition. These venoms presented higher caseinolytic, collagenolytic and coagulant activities than the venoms without these regions recognized by WB. Mass spectrometry analyses performed on two individuals revealed that these individuals present, in addition to higher protein concentrations, other exclusive proteins in their composition. When these same two samples were tested in vivo, the results also showed higher lethality in these venoms, but lower hemorrhagic activity than in the venoms without these regions recognized by WB. In conclusion, some Bothrops moojeni specimens differ in venom composition, which may have implications in envenomation. Moreover, the high individual venom variability found in this species demonstrates the importance to work with individual analyses in studies involving intraspecific venom variability and venom evolution.

Rapid Identification of Phospholipase A₂ Transcripts from Snake Venoms

Phospholipase A₂ (PLA₂) is a major component in snake venoms and it is found in many different isoforms. To identify transcripts encoding different PLA₂ isoforms, we developed a simple, rapid procedure. Total RNA was extracted from the venoms of three cottonmouth snakes and two diamondback rattlesnakes, and further reverse-transcribed into complementary DNA (cDNA). Using one pair of cottonmouth PLA₂-specific primers and a Reverse Transcription Polymerase Chain Reaction (RT-PCR) technique, we identified 27 unique full-length PLA₂ transcripts, including nine sequences identical to the previously documented ones in the database and one novel GIII-like PLA₂. Two common transcripts respectively encoding Asp49 and Lys49 PLA₂ isoforms were identified in all three cottonmouth venoms, that contain more PLA₂ transcripts than the diamondback rattlesnake venoms. The placement of cloned PLA₂ transcripts in snake venom PLA₂s was further discussed by phylogenetic analysis. The procedure developed in this study paves the way for accelerated acquisition of transcriptome data on any other venom toxin families. The results obtained are crucial for insight into the structure and function of PLA₂ isoforms for scientific and potential therapeutic purposes.

Defining the role of post-synaptic α-neurotoxins in paralysis due to snake envenoming in humans

Snake venom α-neurotoxins potently inhibit rodent nicotinic acetylcholine receptors (nAChRs), but their activity on human receptors and their role in human paralysis from snakebite remain unclear. We demonstrate that two short-chain α-neurotoxins (SαNTx) functionally inhibit human muscle-type nAChR, but are markedly more reversible than against rat receptors. In contrast, two long-chain α-neurotoxins (LαNTx) show no species differences in potency or reversibility. Mutant studies identified two key residues accounting for this. Proteomic and clinical data suggest that paralysis in human snakebites is not associated with SαNTx, but with LαNTx, such as in cobras. Neuromuscular blockade produced by both subclasses of α-neurotoxins was reversed by antivenom in rat nerve-muscle preparations, supporting its effectiveness in human post-synaptic paralysis.

A Novel Venom-Derived Peptide for Brachytherapy of Glioblastoma: Preclinical Studies in Mice

We developed a bacterial expression system to produce a recombinant disintegrin, vicrostatin (VCN), whose structure is based on a natural disintegrin isolated from southern copperhead snake venom. Our goal is to develop VCN for potential clinical translation as an anti-cancer agent. VCN is a peptide of 69 amino acids with a single tyrosine residue. We have employed VCN as integrin-targeted radionuclide therapy (brachytherapy) for treatment of glioblastoma (GBM, glioma). GBM is a deadly brain cancer that doesn't discriminate between sexes and knows no age limit. We established that the tyrosine residue in VCN can be radioiodinated with full retention of bioactivity. ¹³¹I-VCN was utilized for integrin-targeted radionuclide therapy using mouse models of glioma. The combination of radioiodinated VCN plus temozolomide (a DNA alkylating agent) significantly prolonged survival of glioma-bearing mice. We also obtained similar results using an immunocompetent mouse model and a murine glioma cell line. In summary, as demonstrated in studies reported here we have shown that VCN as targeted radionuclide therapy for GBM has significant translational potential for therapy of this deadly disease.

Transcriptomics-guided bottom-up and top-down venomics of neonate and adult specimens of the arboreal rear-fanged Brown Treesnake, Boiga irregularis, from Guam

The Brown Treesnake (Boiga irregularis) is an arboreal, nocturnal, rear-fanged venomous snake native to northern and eastern regions of Australia, Papua New Guinea and the Solomon Islands. It was inadvertently introduced onto the island of Guam during the late 1940's to early 1950's, and it has caused massive declines and extirpations of the native bird, lizard, and mammal populations. In the current study, we report the characterization of the venom proteome of an adult and a neonate B. irregularis specimens from Guam by a combination of venom gland transcriptomic and venomic analyses. Venom gland transcriptomic analysis of an adult individual identified toxins belonging to 18 protein families, with three-finger toxin isoforms being the most abundantly expressed transcripts, comprising 94% of all venom protein transcript reads. Transcripts for PIII-metalloproteinases, C-type lectins, cysteine-rich secretory proteins, acetylcholinesterases, natriuretic peptides, ficolins, phospholipase A₂ (PLA₂) inhibitors, PLA₂s, vascular endothelial growth factors, Kunitz-type protease inhibitors, cystatins, phospholipase Bs, cobra venom factors, waprins, SVMP inhibitors, matrix metalloproteinases, and hyaluronidases were also identified, albeit, at very low abundances ranging from 0.05% to 1.7% of the transcriptome. The venom proteomes of neonate and adult B. irregularis were also both overwhelmingly (78 and 84%, respectively) dominated by monomeric and dimeric 3FTxs, followed by moderately abundant (21% (N) and 13% (A)) CRISPs, low abundance (1% (N), 3% (A)) PIII-SVMPs, and very low abundance (<0.01%) PLA₂ and SVMP inhibitors. The differences in relative toxin abundances identified between neonate and adult snakes likely correlates to shifts in prey preference between the two age classes, from nearly-exclusively lizards to lizards, birds and small mammals. Immunoaffinity antivenomics with experimentally designed rabbit anti-Brown Treesnake (anti-BTS) venom IgGs against homologous venom from adult snakes demonstrated that CRISPs, PIII-SVMPs, and 60-70% of 3FTxs were effectively immunocaptured. Western blot analysis showed that all venom proteins were recognized by anti-BTS IgGs, and cross-reactivity with other rear-fanged snake venoms was also observed. Incubation of anti-BTS venom IgGs with crude B. irregularis venom resulted in a significant decrease in proteolytic (SVMP) activity against azocasein. These results provide the first comparative venomic and anti-venomic analysis of neonate and adult B. irregularis from Guam, further highlighting evolutionary trends in venom composition among rear-fanged venomous snakes.

SIGNIFICANCE PARAGRAPH

The Brown Treesnake (Boiga irregularis) has caused extensive ecological and economic damage to the island of Guam where it has become a classic example of the negative impacts of invasive species. In the current study, we report the first combined transcriptomic and proteomic analysis of B. irregularis venom of Guam origin. The transcriptome of an adult snake contained toxin sequences belonging to 18 protein families, with three-finger toxin (3FTx) isoforms being the most abundant and representing 94% of all venom protein transcript reads. Our bottom-up and top-down venomic analyses confirmed that 3FTxs are the major components of B. irregularis venom, and a comparative analysis of neonate and adult venoms demonstrate a clear ontogenetic shift in toxin abundance, likely driven by dietary variation between the two age classes. Second-generation antivenomics and Western blot analysis using purified anti-Brown Treesnake rabbit serum IgGs (anti-BTS IgGs) showed strong immunoreactivity toward B. irregularis venom. Interestingly, our anti-BTS IgGs did not cross-react with 3FTxs found in several other rear-fanged snake venoms, or against 3FTxs in the venom of the elapid Ophiophagus hannah, indicating that epitopes in these 3FTx molecules are quite distinct.

Trends in the Evolution of Snake Toxins Underscored by an Integrative Omics Approach to Profile the Venom of the Colubrid Phalotris mertensi

Only few studies on snake venoms were dedicated to deeply characterize the toxin secretion of animals from the Colubridae family, despite the fact that they represent the majority of snake diversity. As a consequence, some evolutionary trends observed in venom proteins that underpinned the evolutionary histories of snake toxins were based on data from a minor parcel of the clade. Here, we investigated the proteins of the totally unknown venom from Phalotris mertensi (Dipsadinae subfamily), in order to obtain a detailed profile of its toxins and to appreciate evolutionary tendencies occurring in colubrid venoms. By means of integrated omics and functional approaches, including RNAseq, Sanger sequencing, high-resolution proteomics, recombinant protein production, and enzymatic tests, we verified an active toxic secretion containing up to 21 types of proteins. A high content of Kunitz-type proteins and C-type lectins were observed, although several enzymatic components such as metalloproteinases and an L-amino acid oxidase were also present in the venom. Interestingly, an arguable venom component of other species was demonstrated as a true venom protein and named svLIPA (snake venom acid lipase). This finding indicates the importance of checking the actual protein occurrence across species before rejecting genes suggested to code for toxins, which are relevant for the discussion about the early evolution of reptile venoms. Moreover, trends in the evolution of some toxin classes, such as simplification of metalloproteinases and rearrangements of Kunitz and Wap domains, parallel similar phenomena observed in other venomous snake families and provide a broader picture of toxin evolution.

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.

A Heterologous Multiepitope DNA Prime/Recombinant Protein Boost Immunisation Strategy for the Development of an Antiserum against Micrurus corallinus (Coral Snake) Venom

Background

Envenoming by coral snakes (Elapidae: Micrurus), although not abundant, represent a serious health threat in the Americas, especially because antivenoms are scarce. The development of adequate amounts of antielapidic serum for the treatment of accidents caused by snakes like Micrurus corallinus is a challenging task due to characteristics such as low venom yield, fossorial habit, relatively small sizes and ophiophagous diet. These features make it difficult to capture and keep these snakes in captivity for venom collection. Furthermore, there are reports of antivenom scarcity in USA, leading to an increase in morbidity and mortality, with patients needing to be intubated and ventilated while the toxin wears off. The development of an alternative method for the production of an antielapidic serum, with no need for snake collection and maintenance in captivity, would be a plausible solution for the antielapidic serum shortage.

Methods and Findings

In this work we describe the mapping, by the SPOT-synthesis technique, of potential B-cell epitopes from five putative toxins from M. corallinus, which were used to design two multiepitope DNA strings for the genetic immunisation of female BALB/c mice. Results demonstrate that sera obtained from animals that were genetically immunised with these multiepitope constructs, followed by booster doses of recombinant proteins lead to a 60% survival in a lethal dose neutralisation assay.

Conclusion

Here we describe that the genetic immunisation with a synthetic multiepitope gene followed by booster doses with recombinant protein is a promising approach to develop an alternative antielapidic serum against M. corallinus venom without the need of collection and the very challenging maintenance of these snakes in captivity.

Coral snakes are a group of deadly venomous snakes that exhibit a characteristic red, yellow/white, and black coloured banding pattern. Accidents involving these snakes tend to be very severe or even lethal, causing peripheral nervous system depression with muscle paralysis and vasomotor instability. The only acceptable medical treatment for snakebite accidents is the administration of an antivenom, generally produced by immunising horses with the snake venom. Nonetheless, for what concerns the antielapidic serum production in Brazil, the total amount of venom available for horse immunisations is insufficient. This is mainly due to the small size of coral snake glands, their underground life style, combined with its very low survival rates in captivity. Moreover, cases of patients being intubated and ventilated as a consequence of antivenom shortage in USA have also been registered. In this work, we present an alternative method for the development of antielapidic serum, which does not rely upon snake capture. This serum was produced by a heterologous DNA prime—with a multiepitope DNA string coding for the most reactive epitopes from the most abundant toxins of M. corallinus, a coral snake which occupy highly populated areas in Brazil—followed by recombinant multiepitope protein boost immunisation of mice.

Isolation, characterization and antigenic cross-reactivities of the major hemorrhagin from Cryptelytrops purpureomaculatus venom

The major hemorrhagin from C. purpureomaculatus (mangrove pit viper) venom was purified to homogeneity and termed Maculatoxin. Maculatoxin has a molecular weight of 38 kDa as determined by SDS-PAGE. It is an acidic protein (pI= 4.2) and exhibited proteolytic and hemorrhagic activities (MHD10 = 0.84 microg in mice) but was not lethal to mice at a dose of 1 microg/g. The hemorrhagic activity of Maculatoxin was completely inactivated by EDTA and partially inhibited by ATP and citrate. The N-terminal sequence of Maculatoxin (TPEQQRFPPTYIDLGIFVDHGMYAT) shares a significant degree of homology with the metalloprotease domain of other venom hemorrhagins. Indirect ELISA showed anti-Maculatoxin cross reacted with protein components of many snake venoms. In the double-sandwich ELISA, however, anti-Maculatoxin cross-reacted only with venoms of certain species of the Trimeresurus (Asia lance-head viper) complex, and the results support the recent proposed taxonomy changes concerning the Trimeresurus complex.

Molecular evolution of vertebrate neurotrophins: co-option of the highly conserved nerve growth factor gene into the advanced snake venom arsenalf

Neurotrophins are a diverse class of structurally related proteins, essential for neuronal development, survival, plasticity and regeneration. They are characterized by major family members, such as the nerve growth factors (NGF), brain-derived neurotrophic factors (BDNF) and neurotrophin-3 (NT-3), which have been demonstrated here to lack coding sequence variations and follow the regime of negative selection, highlighting their extremely important conserved role in vertebrate homeostasis. However, in stark contrast, venom NGF secreted as part of the chemical arsenal of the venomous advanced snake family Elapidae (and to a lesser extent Viperidae) have characteristics consistent with the typical accelerated molecular evolution of venom components. This includes a rapid rate of diversification under the significant influence of positive-selection, with the majority of positively-selected sites found in the secreted β-polypeptide chain (74%) and on the molecular surface of the protein (92%), while the core structural and functional residues remain highly constrained. Such focal mutagenesis generates active residues on the toxin molecular surface, which are capable of interacting with novel biological targets in prey to induce a myriad of pharmacological effects. We propose that caenophidian NGFs could participate in prey-envenoming by causing a massive release of chemical mediators from mast cells to mount inflammatory reactions and increase vascular permeability, thereby aiding the spread of other toxins and/or by acting as proapoptotic factors. Despite their presence in reptilian venom having been known for over 60 years, this is the first evidence that venom-secreted NGF follows the molecular evolutionary pattern of other venom components, and thus likely participates in prey-envenomation.

Unusual stability of messenger RNA in snake venom reveals gene expression dynamics of venom replenishment

Venom is a critical evolutionary innovation enabling venomous snakes to become successful limbless predators; it is therefore vital that venomous snakes possess a highly efficient venom production and delivery system to maintain their predatory arsenal. Here, we exploit the unusual stability of messenger RNA in venom to conduct, for the first time, quantitative PCR to characterise the dynamics of gene expression of newly synthesised venom proteins following venom depletion. Quantitative PCR directly from venom enables real-time dynamic studies of gene expression in the same animals because it circumvents the conventional requirement to sacrifice snakes to extract mRNA from dissected venom glands. Using qPCR and proteomic analysis, we show that gene expression and protein re-synthesis triggered by venom expulsion peaks between days 3-7 of the cycle of venom replenishment, with different protein families expressed in parallel. We demonstrate that venom re-synthesis occurs very rapidly following depletion of venom stores, presumably to ensure venomous snakes retain their ability to efficiently predate and remain defended from predators. The stability of mRNA in venom is biologically fascinating, and could significantly empower venom research by expanding opportunities to produce transcriptomes from historical venom stocks and rare or endangered venomous species, for new therapeutic, diagnostic and evolutionary studies.

Isolation, functional, and partial biochemical characterization of galatrox, an acidic lectin from Bothrops atrox snake venom

Snake venom lectins have been studied in regard to their chemical structure and biological functions. However, little is known about lectins isolated from Bothrops atrox snake venom. We report here the isolation and partial functional and biochemical characterization of an acidic glycan-binding protein called galatrox from this venom. This lectin was purified by affinity chromatography using a lactosyl-sepharose column, and its homogeneity and molecular mass were evaluated by high-performance liquid chromatography, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry. The purified galatrox was homogeneous and characterized as an acidic protein (pI 5.2) with a monomeric and dimeric molecular mass of 16.2 and 32.5 kDa, respectively. Alignment of N-terminal and internal amino acid sequences of galatrox indicated that this protein exhibits high homology to other C-type snake venom lectins. Galatrox showed optimal hemagglutinating activity at a concentration of 100 μg/ml and this effect was drastically inhibited by lactose, ethylenediaminetetraacetic acid, and heating, which confirmed galatrox's lectin activity. While galatrox failed to induce the same level of paw edema or mast cell degranulation as B. atrox crude venom, galatrox did alter cellular viability, which suggested that galatrox might contribute to venom toxicity by directly inducing cell death.

Biological and proteomic analysis of venom from the Puerto Rican Racer (Alsophis portoricensis: Dipsadidae)

The Puerto Rican Racer Alsophis portoricensis is known to use venom to subdue lizard prey, and extensive damage to specific lizard body tissues has been well documented. The toxicity and biochemistry of the venom, however, has not been explored extensively. We employed biological assays and proteomic techniques to characterize venom from A. portoricensis anegadae collected from Guana Island, British Virgin Islands. High metalloproteinase and gelatinase, as well as low acetylcholinesterase and phosphodiesterase activities were detected, and the venom hydrolyzed the alpha-subunit of human fibrinogen very rapidly. SDS-PAGE analysis of venoms revealed up to 22 protein bands, with masses of approximately 5-160 kDa; very little variation among individual snakes or within one snake between venom extractions was observed. Most bands were approximately 25-62 kD, but MALDI-TOF analysis of crude venom indicated considerable complexity in the 1.5-13 kD mass range, including low intensity peaks in the 6.2-8.8 kD mass range (potential three-finger toxins). MALDI-TOF/TOF MS analysis of tryptic peptides confirmed that a 25 kDa band was a venom cysteine-rich secretory protein (CRiSP) with sequence homology with tigrin, a CRiSP from the natricine colubrid Rhabdophis tigrinus. The venom was quite toxic to NSA mice (Mus musculus: LD(50)=2.1 microg/g), as well as to Anolis lizards (A. carolinensis: 3.8 microg/g). Histology of the venom gland showed distinctive differences from the supralabial salivary glands (serous vs. mucosecretory), and like the Brown Treesnake (Boiga irregularis), another rear-fanged snake, serous secretory cells are arranged in densely packed secretory tubules, with little venom present in tubule lumina. These results clearly demonstrate that venom from A. portoricensis shares components with venoms of front-fanged snakes as well as with other rear-fanged species. Venom from A. portoricensis, in particular the prominent metalloproteinase activity, likely serves an important trophic function by facilitating prey handling and predigestion of prey.

Purification and characterization of a cysteine-rich secretory protein from Philodryas patagoniensis snake venom

Cysteine-rich secretory proteins (CRiSPs) are widespread in reptile venoms, but most have functions that remain unknown. In the present study we describe the purification and characterization of a CRiSP (patagonin) from the venom of the rear-fanged snake Philodryas patagoniensis, and demonstrate its biological activity. Patagonin is a single-chain protein, exhibiting a molecular mass of 24,858.6 Da, whose NH(2)-terminal and MS/MS-derived sequences are nearly identical to other snake venom CRiSPs. The purified protein hydrolyzed neither azocasein nor fibrinogen, and it could induce no edema, hemorrhage or inhibition of platelet adhesion and aggregation. In addition, patagonin did not inhibit contractions of rat aortic smooth muscle induced by high K(+). However, it caused muscular damage to murine gastrocnemius muscle, an action that has not been previously described for any snake venom CRiSPs. Thus, patagonin will be important for studies of the structure-function and evolutionary relationships of this family of proteins that are widely distributed among snake venoms.

Crotalus durissus collilineatus venom gland transcriptome: analysis of gene expression profile

Crotalus durissus rattlesnakes are responsible for the most lethal cases of snakebites in Brazil. Crotalus durissus collilineatus subspecies is related to a great number of accidents in Southeast and Central West regions, but few studies on its venom composition have been carried out to date. In an attempt to describe the transcriptional profile of the C. durissus collilineatus venom gland, we generated a cDNA library and the sequences obtained could be identified by similarity searches on existing databases. Out of 673 expressed sequence tags (ESTs) 489 produced readable sequences comprising 201 singletons and 47 clusters of two or more ESTs. One hundred and fifty reads (60.5%) produced significant hits to known sequences. The results showed a predominance of toxin-coding ESTs instead of transcripts coding for proteins involved in all cellular functions. The most frequent toxin was crotoxin, comprising 88% of toxin-coding sequences. Crotoxin B, a basic phospholipase A(2) (PLA(2)) subunit of crotoxin, was represented in more variable forms comparing to the non-enzymatic subunit (crotoxin A), and most sequences coding this molecule were identified as CB1 isoform from Crotalus durissus terrificus venom. Four percent of toxin-related sequences in this study were identified as growth factors, comprising five sequences for vascular endothelial growth factor (VEGF) and one for nerve growth factor (NGF) that showed 100% of identity with C. durissus terrificus NGF. We also identified two clusters for metalloprotease from PII class comprising 3% of the toxins, and two for serine proteases, including gyroxin (2.5%). The remaining 2.5% of toxin-coding ESTs represent singletons identified as homologue sequences to cardiotoxin, convulxin, angiotensin-converting enzyme inhibitor and C-type natriuretic peptide, Ohanin, crotamin and PLA(2) inhibitor. These results allowed the identification of the most common classes of toxins in C. durissus collilineatus snake venom, also showing some unknown classes for this subspecies and even for C. durissus species, such as cardiotoxins and VEGF.

[Effects of snake venom cystatin gene on gene expression profiles in mouse melanoma cell line B16F1]

BACKGROUND & OBJECTIVE

Previously, we have demonstrated that snake venom cystatin (sv-cystatin) plays an important role in tumor invasion and metastasis. This study was to investigate the effects of sv-cystatin on the gene expression profile of mouse melanoma B16F1 cells.

METHODS

pcDNA3.1/sv-cystatin plasmid was constructed and transfected into B16F1 using lipofectamine. Differentially expressed genes between B16F1 transfected with pcDNA3.1/sv-cystatin and pcDNA3.1 were analysed by high throughput microarray technique. Five up-regulated genes and five down-regulated genes were confirmed by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Out of 1218 transcript species, 45 showed altered expressions: 21 were up-regulated and 24 were down-regulated. These altered genes are involved in cell adhesion and migration, cell immunomodulation, proliferation, differentiation, apoptosis, as well as gene transcription and intra-cellular signal transduction. RT-PCR results of 10 alerted genes were in accordance with the microarray data.

CONCLUSIONS

Sv-cystatin not only inhibits the extracellular matrix, but may also possess other diverse biological functions, including cell immunomodulation, proliferation and differentiation, apoptosis, gene transcription and intra-cellular signal transduction.

Evolution of an Arsenal

Venom is a key innovation underlying the evolution of advanced snakes (Caenophidia). Despite this, very little is known about venom system structural diversification, toxin recruitment event timings, or toxin molecular evolution. A multidisciplinary approach was used to examine the diversification of the venom system and associated toxins across the full range of the approximately 100 million-year-old advanced snake clade with a particular emphasis upon families that have not secondarily evolved a front-fanged venom system ( approximately 80% of the 2500 species). Analysis of cDNA libraries revealed complex venom transcriptomes containing multiple toxin types including three finger toxins, cobra venom factor, cysteine-rich secretory protein, hyaluronidase, kallikrein, kunitz, lectin, matrix metalloprotease, phospholipase A(2), snake venom metalloprotease/a disintegrin and metalloprotease, and waprin. High levels of sequence diversity were observed, including mutations in structural and functional residues, changes in cysteine spacing, and major deletions/truncations. Morphological analysis comprising gross dissection, histology, and magnetic resonance imaging also demonstrated extensive modification of the venom system architecture in non-front-fanged snakes in contrast to the conserved structure of the venom system within the independently evolved front-fanged elapid or viperid snakes. Further, a reduction in the size and complexity of the venom system was observed in species in which constriction has been secondarily evolved as the preferred method of prey capture or dietary preference has switched from live prey to eggs or to slugs/snails. Investigation of the timing of toxin recruitment events across the entire advanced snake radiation indicates that the evolution of advanced venom systems in three front-fanged lineages is associated with recruitment of new toxin types or explosive diversification of existing toxin types. These results support the role of venom as a key evolutionary innovation in the diversification of advanced snakes and identify a potential role for non-front-fanged venom toxins as a rich source for lead compounds for drug design and development.

Cloning, expression and characterization of two C-type lectins from the venom gland of Bungarus multicinctus

C-type lectins found in many animals are non-enzymatic proteins and able to bind with mono- and oligosaccharides in a Ca(2+)-dependent fashion. Here, we report the cloning of two C-type lectins named BML-1 and BML-2 from the venom gland of Bungarus multicinctus, and expression of their mature peptides with 135 and 137 amino acids as inclusion bodies. Recombinant BML-1 and BML-2 proteins with 135 amino acids formed monomers, and those with 137 amino acids formed homodimers and monomers and both of them displayed certain hemagglutinating activity to rabbit erythrocytes. The results of Western blotting and immuno-affinity chromatography demonstrated that C-type lectins in B. multicinctus formed dimers in physiological conditions, and their molecular weight is lower than previous predictions. This is the first report of the cloning of the BML-2 gene from the venom gland of B. multicinctus, as well as an investigation of its confirmation and biological functions.

Neurotropic effects of venoms and other factors that promote prey acquisition

Mammals envenomed by either the Eastern diamondback rattlesnake (Crotalus adamanteus) or the cottonmouth (Agkistrodon piscivorus piscivorus) exhibit an immediate but transitory pupillar contraction, a parasympathomimetic effect mediated through the ciliary ganglion that can be prevented by a retrobulbar injection of anesthetic. The venom of the cottonmouth injected into the lymph spaces of the frog (Rana pipiens) produces an immediate and total collapse of the lung sacs. Applied locally to the surface, it produces a constriction that eventually collapses the entire sac. Tests of venoms and toxins from both anterior and posterior parts of the venom apparatus indicate that the lung-collapsing moiety originates in the accessory, not the main portion of the venom gland. This is the first example of a functional specialization within the whole structure. It seems that this factor is elaborated primarily in snakes that prey upon frogs, although insufficient data are available from this study to confirm this. In both reptile species, the predatory strike is accompanied by an immediate effect, perhaps mediated by the parasympathetic nervous system, designed to incapacitate the prey and facilitate capture. These effects cannot now be attributed to neurotoxins because the effect of the former is transitory (and not lethal) and neither has been purified sufficiently to determine potency or structure. Both take part in securing, but not killing, the prey, and both directly oppose the sympathetic nervous system "fright-fight/flight" response. Evidence is presented to support the possibility that known epigenetic mechanisms are capable of effecting heritable changes in gene expression that could allow for the development of factors that facilitate prey acquisition and promote rapid adaptation to environmental change.

Molecular barcoding, DNA from snake venom, and toxinological research: Considerations and concerns

The problem of species identification in toxinological research and solutions such as molecular barcoding and DNA extraction from venom samples are addressed. Molecular barcoding is controversial with both perceived advantages and inherent problems. A method of species identification utilizing mitochondrial DNA from venom has been identified. This method could result in deemphasizing the importance of obtaining detailed information on the venom source prior to analysis. Additional concerns include; a cost prohibitive factor, intraspecific venom variation, and venom processing issues. As researchers demand more stringent records and verification, venom suppliers may be prompted to implement improved methods and controls.

Molecular and functional diversity of vascular endothelial growth factors

Members of the vascular endothelial growth factor (VEGF) family are crucial regulators of neovascularization and are classified as cystine knot growth factors that specifically bind cellular receptor tyrosine kinases VEGFR-1, VEGFR-2, and VEGFR-3 with high but variable affinity and selectivity. The VEGF family has recently been expanded and currently comprises seven members: VEGF-A, VEGF-B, placenta growth factor (PlGF), VEGF-C, VEGF-D, viral VEGF (also known as VEGF-E), and snake venom VEGF (also known as VEGF-F). Although all members are structurally homologous, there is molecular diversity among the subtypes, and several isoforms, such as VEGF-A, VEGF-B, and PlGF, are generated by alternative exon splicing. These splicing isoforms exhibit differing properties, particularly in binding to co-receptor neuropilins and heparin. VEGF family proteins play multiple physiological roles, such as angiogenesis and lymphangiogenesis, while exogenous members (viral and snake venom VEGFs) display activities that are unique in physiology and function. This review will highlight the molecular and functional diversity of VEGF family proteins.

Integrins in Drug Targeting-RGD Templates in Toxins

Integrins are a family of heterodimeric receptors, which modulate many cellular processes including: growth, death (apoptosis), adhesion, migration, and invasion by activating several signaling pathways. Integrin-binding RGD (arginine-glycine-aspartic acid) is found in several important extracellular matrix proteins which serve as adhesive integrin ligands. The RGD motif has also been found in many toxins from snake venom and other sources that specifically inhibit integrin binding function and serve as potent integrin antagonists, particularly of platelet aggregation and integrin-mediated cell adhesion. Many of these proteins have potential as therapeutic agents which can target integrins directly. Structural and functional studies of several RGD-containing toxins suggest that the inhibitory potency of these proteins lies in subtle positional requirements of the tripeptide RGD at the tip of a flexible loop, a structural feature for binding to integrins. In addition, amino acid residues in this loop in close vicinity to the RGD-motif determine the integrin-binding specificity and selectivity. This review will present a review of integrin structure and function, and of disintegrin structural features responsible for their activity as antagonists of integrin function. The use of integrins in drug targeting and integrins as targets for drug delivery by using the RGD as a template structure will also be discussed.

Some aspects of the venom proteome of the Colubridae snakePhilodryas olfersiirevealed from a Duvernoy's (venom) gland transcriptome

We investigated the putative toxins of Philodryas olfersii (Colubridae), a representative of a family of snakes neglected in venom studies despite their growing medical importance. Transcriptomic data of the venom gland complemented by proteomic analysis of the gland secretion revealed the presence of major toxin classes from the Viperidae family, including serine proteases, metalloproteases, C-type lectins, Crisps, and a C-type natriuretic peptide (CNP). Interestingly, the phylogenetic analysis of the CNP precursor showed it as a linker between two related precursors found in Viperidae and Elapidae snakes. We suggest that these precursors constitute a monophyletic group derived from the vertebrate CNPs.

Molecular Cloning of Disintegrin-like Transcript BA-5A from a Bitis arietans Venom Gland cDNA Library: A Putative Intermediate in the Evolution of the Long-Chain Disintegrin Bitistatin

We report the cloning and sequence analysis of BA-5A from a venom gland cDNA library of the puff adder, Bitis arietans, that encodes a novel ECD-disintegrin-like domain. BA-5A is a unique PII disintegrin. It contains the 16 cysteine residues that are conserved in all known disintegrin-like domains of ADAM proteins and snake venom metalloproteinases but lacks the cysteine-rich domain. These features suggest that BA-5A may represent an intermediate in the evolutionary pathway of the long disintegrin bitistatin and that removal of the cysteine-rich domain and loss of the PIII-specific disulfide bond were separate events along the structural diversification pathway of disintegrins, the former predating the latter. The protein family composition of the Bitis arietans venom, as determined by combination of reversed-phase HPLC and proteomic analysis, was as follows: Zn(2+)-metalloproteinase (38.5%), serine proteinase (19.5%), disintegrin (17.8%), C-type lectin-like (13.2%), PLA(2) (4.3%), Kunitz-type inhibitor (4.1%), cystatin (1.7%), and unknown (0.9%). BA-5A could not be detected in the venom proteome of Bitis arietans. The occurrence of this very low-abundance (< 0.05%) or nonexpressed disintegrin transcript indicates a hitherto unrecognized structural diversity of this protein family. Whether BA-5A plays a physiological role or represents an orphan protein which could eventually evolve a role in the adaptation of snakes to changing ecological niches and prey habits deserves further investigation.

A general method for the synthesis of 2'-O-cyanoethylated oligoribonucleotides having promising hybridization affinity for DNA and RNA and enhanced nuclease resistance

[reaction: see text] An effective method for the synthesis of 2'-O-cyanoethylated oligoribonucleotides as a new class of 2'-O-modified RNAs was developed. The reaction of appropriately protected ribonucleoside derivatives with acrylonitrile in t-BuOH in the presence of Cs2CO3 gave 2'-O-cyanoethylated ribonucleoside derivatives in excellent yields, which were converted by a successive selective deprotection/protection strategy to 2'-O-cyanoethylated 5'-O-dimethoxytritylribonucleoside 3'-phosphoramidite derivatives in high yields. Fully 2'-O-cyanoethylated oligoribonucleotides, (Uce)12 and (GceAceCceUce)3, were successfully synthesized in the phosphoramidite approach by use of the phosphoramidite building blocks. It was also found that oligoribonucleotides having a 2'-O-cyanoethylated ribonucleoside (Uce, Cce, Ace, or Gce) could be obtained by the selective removal of the TBDMS group from fully protected oligoribonucleotide intermediates without loss of the cyanoethyl group by use of NEt3 x 3HF as a desilylating reagent. The detailed T(m) experiments revealed that oligoribonucleotides containing 2'-O-cyanoethylated ribonucleosides have higher hybridization affinity for both DNA and RNA than the corresponding unmodified and 2'-O-methylated oligoribonucleotides. In addition, introduction of a cyanoethyl group into the 2'-position of RNA resulted in significant increase of nuclease resistance toward snake venom and bovine spleen phosphodiesterases compared with that of the methyl group.

Mitochondrial DNA sequences from dried snake venom: a DNA barcoding approach to the identification of venom samples

Outdated nomenclature and incorrect taxonomic characterisation of snake venoms in the current toxinological literature have serious implications for the replicability of results from snake venom toxin research. The situation has not improved, despite attempts to supply toxinologists with regular updates on snake systematics. Here, we demonstrate the successful extraction of DNA, and subsequent sequencing of the mitochondrial 12S gene, from dried snake venoms. This approach offers a new and potentially straightforward method for accurate species identification. Mitochondrial DNA (mtDNA) sequences isolated from snake venom can be used to clarify or validate snake species identification through comparison against existing sequences in the GenBank database, and through phylogenetic analyses with other sequences. Pooled venoms can also be screened a priori for the presence of multiple species, and the species names on the labels of commercial venoms verified. Moreover, if the species from which the venom sample has been taken is known, and the specimen is available as a voucher, the mtDNA sequence of the haplotype isolated from that species venom sample could serve as a sequence standard (or 'DNA barcode') for that species. Our new method of DNA barcoding venoms ensures the identification of venoms even after future taxonomic changes.

Glial inflammation and neurodegeneration induced by candoxin, a novel neurotoxin from Bungarus candidus venom: global gene expression analysis using microarray

Candoxin (PDB #1JGK), a three-finger neurotoxin from Bungarus candidus venom, inhibits post-synaptic neuromuscular and neuronal alpha7nACh-receptors, and induces delayed cell-death throughout the glial population. When applied to cultured human glial cell lines, candoxin (CDX) induced cell death in a concentration (EC(50) approximately 1muM) and time dependent manner. Results of TUNEL-histochemistry further confirm CDX-induced brain (hippocampus, frontal cortex, and temporal regions) damage when administered intracerebroventricularly (i.c.v) in adult mice. In this study, we explored differential gene expression profiles following exposure of human glial (Hs 683) cell lines to CDX at various time intervals using Affymetrix-GeneChips. By means of MAS and GeneSpring analyses, 105 genes whose expression was significantly (P<0.01) altered by at least 3-fold were selected. Results of the genome analysis reveal that the potential role of CDX at molecular level involves the regulation of genes in signal transduction, ubiquitin-inflammation, mitochondrial-dysfunction, and damage-response pathways. In addition, using QRT-PCR and rationally designed specific CDX-binding peptide (P-NT.II), we identified the genes-IL7R, IL13RA2, IL-1beta, TNFRSF12A, GADD45A, CD44 and IFI44-that might play an important role in CDX-induced glial inflammation, DNA-damage and degeneration. These findings reveal new insight into the molecular mechanisms of glial-driven neurodegeneration after exposure to neurotoxins.

Identification and analysis of venom gland-specific genes from the coastal taipan (Oxyuranus scutellatus) and related species

Australian terrestrial elapid snakes contain amongst the most potently toxic venoms known. However, despite the well-documented clinical effects of snake bite, little research has focussed on individual venom components at the molecular level. To further characterise the components of Australian elapid venoms, a complementary (cDNA) microarray was produced from the venom gland of the coastal taipan (Oxyuranus scutellatus) and subsequently screened for venom gland-specific transcripts. A number of putative toxin genes were identified, including neurotoxins, phospholipases, a pseudechetoxin-like gene, a venom natriuretic peptide and a nerve growth factor together with other genes involved in cellular maintenance. Venom gland-specific components also included a calglandulin-like protein implicated in the secretion of toxins from the gland into the venom. These toxin transcripts were subsequently identified in seven other related snake species, producing a detailed comparative analysis at the cDNA and protein levels. This study represents the most detailed description to date of the cloning and characterisation of different genes associated with envenomation from Australian snakes.

Structural considerations of the snake venom metalloproteinases, key members of the M12 reprolysin family of metalloproteinases

The importance of proteinases in the pathologies associated with Viperid envenoming has long been appreciated. Over the past 40 years substantial research has clearly implicated metalloproteinases in the venom (snake venom metalloproteinases; SVMPs) as playing key roles in the development of such symptoms as hemorrhage, edema, hypotension, hypovolemia, inflammation and necrosis. In spite of this wealth of information there are still many unresolved questions pertaining to the structural basis for the various SVMPS giving rise to the diversity of activities. In this short review we will not attempt to provide an exhaustive collation of structural studies on the SVMPs; however, we will give a brief outline of the structural classification of the SVMPs; as well as relate them to the other members of the reprolysin family of metalloproteinases, the ADAMs. The information put forth in the text does not allow specific conclusions to be drawn on the structural basis for SVMP functional diversity, but it is our goal that it will allow for the development of testable hypotheses that can be experimentally pursued. What the reader will observe is that there are very interesting structural features displayed by the various SVMP classes and subclasses that provide insight into their functional characteristics.

From genome to "venome": molecular origin and evolution of the snake venom proteome inferred from phylogenetic analysis of toxin sequences and related body proteins

This study analyzed the origin and evolution of snake venom proteome by means of phylogenetic analysis of the amino acid sequences of the toxins and related nonvenom proteins. The snake toxins were shown to have arisen from recruitment events of genes from within the following protein families: acetylcholinesterase, ADAM (disintegrin/metalloproteinase), AVIT, complement C3, crotasin/beta defensin, cystatin, endothelin, factor V, factor X, kallikrein, kunitz-type proteinase inhibitor, LYNX/SLUR, L-amino oxidase, lectin, natriuretic peptide, betanerve growth factor, phospholipase A(2), SPla/Ryanodine, vascular endothelial growth factor, and whey acidic protein/secretory leukoproteinase inhibitor. Toxin recruitment events were found to have occurred at least 24 times in the evolution of snake venom. Two of these toxin derivations (CRISP and kallikrein toxins) appear to have been actually the result of modifications of existing salivary proteins rather than gene recruitment events. One snake toxin type, the waglerin peptides from Tropidolaemus wagleri (Wagler's Viper), did not have a match with known proteins and may be derived from a uniquely reptilian peptide. All of the snake toxin types still possess the bioactivity of the ancestral proteins in at least some of the toxin isoforms. However, this study revealed that the toxin types, where the ancestral protein was extensively cysteine cross-linked, were the ones that flourished into functionally diverse, novel toxin multigene families.

Molecular diversity and accelerated evolution of C-type lectin-like proteins from snake venom

A number of C-type lectin-like proteins that affect thrombosis and hemostasis by inhibiting or activating specific platelet membrane receptors or blood coagulation factors have been isolated from the venom of various snake species and characterized and more than 80 have been sequenced. Recent data on the primary sequences and 3D structures of C-type lectins and C-type lectin-like proteins from snake venoms have enabled us to analyze their molecular evolution. Statistical analysis of their cDNA sequences shows that C-type lectin-like proteins, with some exceptions, have evolved in an accelerated manner to acquire their diverse functions. Phylogenetic analysis shows that the A and B chains of C-type lectin-like proteins are clearly separated from C-type lectins and that the A and B chains are further divided into a group of platelet receptor-binding proteins and a group of coagulation factor-binding proteins. Elucidation of the tertiary structures of several C-type lectin-like proteins led to the discovery of a unique domain-swapping interaction between heterodimeric subunits, which creates a concave surface for ligand binding.

Identification and cloning of snake venom vascular endothelial growth factor (svVEGF) from Bothrops erythromelas pitviper

Vascular endothelial growth factors (VEGFs) are among the most important angiogenic proteins found on vertebrates. In the last years, some reports of the occurrence of such proteins in snake venoms are rising the importance of this family of proteins as toxins, since they appear to be involved in many features of Viperidae envenoming, such as hypotension and venom spread through increase in vascular permeability. Here we describe the occurrence of snake venom VEGF in Bothrops erythromelas, a clinical important snake from Northeast of Brazil, through immunodetection and cloning of its cDNA and briefly provide an overview comparison of all recent described svVEGF sequences.

Structure and function of snake venom cysteine-rich secretory proteins

Cysteine-rich secretory proteins (CRISPs) are primarily found in the epididymis of mammals and are expressed in diverse organisms. However, the functions of most CRISPs remain unknown. Recent studies reveal that CRISPs are widely distributed in snake venoms and that they inhibit smooth muscle contraction and cyclic nucleotide-gated ion channels. In this review, we discuss recent findings on several snake venom-derived CRISPs.

Bitis gabonica (Gaboon viper) snake venom gland: toward a catalog for the full-length transcripts (cDNA) and proteins

The venom gland of the snake Bitis gabonica (Gaboon viper) was used for the first time to construct a unidirectional cDNA phage library followed by high-throughput sequencing and bioinformatic analysis. Hundreds of cDNAs were obtained and clustered into contigs. We found mostly novel full-length cDNA coding for metalloproteases (P-II and P-III classes), Lys49-phospholipase A2, serine proteases with essential mutations in the active site, Kunitz protease inhibitors, several C-type lectins, bradykinin-potentiating peptide, vascular endothelial growth factor, nucleotidases and nucleases, nerve growth factor, and L-amino acid oxidases. Two new members of the recently described short coding region family of disintegrin, displaying RGD and MLD motifs are reported. In addition, we have identified for the first time a cytokine-like molecule and a multi-Kunitz protease inhibitor in snake venoms. The CLUSTAL alignment and the unrooted cladograms for selected families of B. gabonica venom proteins are also presented. A significant number of sequences were devoid of database matches, suggesting that their biologic function remains to be identified. This paper also reports the N-terminus of the 15 most abundant venom proteins and the sequences matching their corresponding transcripts. The electronic version of this manuscript, available on request, contains spreadsheets with hyperlinks to FASTA-formatted files for each contig and the best match to the GenBank and Conserved Domain Databases, in addition to CLUSTAL alignments of each contig. We have thus generated a comprehensive catalog of the B. gabonica venom gland, containing for each secreted protein: (i) the predicted molecular weight, (ii) the predicted isoelectric point, (iii) the accession number, and (iv) the putative function. The role of these molecules is discussed in the context of the envenomation caused by the Gaboon viper.

Biochemical characterization of phospholipase A2 (trimorphin) from the venom of the Sonoran Lyre Snake Trimorphodon biscutatus lambda (family Colubridae)

Phospholipases A(2) (PLA(2)), common venom components and bioregulatory enzymes, have been isolated and sequenced from many snake venoms, but never from the venom (Duvernoy's gland secretion) of colubrid snakes. We report for the first time the purification, biochemical characterization and partial sequence of a PLA(2) (trimorphin) from the venom of a colubrid snake, Trimorphodon biscutatus lambda (Sonoran Lyre Snake). Specific phospholipase activity of the purified PLA(2) was confirmed by enzyme assays. The molecular weight of the enzyme has been determined by SDS-PAGE and mass spectrometry to be 13,996 kDa. The sequence of 50 amino acid residues from the N-terminal has been identified and shows a high degree of sequence homology to the type IA PLA(2)s, especially the Asp-49 enzymes. The Cys-11 residue, characteristic of the group IA PLA(2)s, and the Ca(2+) binding loop residues (Tyr-28, Gly-30, Gly-32, and Asp-49) are conserved. In addition, the His-48 residue, a key component of the active site, is also conserved in trimorphin. The results of phylogenetic analysis on the basis of amino acid sequence homology demonstrate that trimorphin belongs to the type IA family, and it appears to share a close evolutionary relationship with the PLA(2)s from hydrophiine elapid snakes (sea snakes and Australian venomous snakes).

Snake postsynaptic neurotoxins: gene structure, phylogeny and applications in research and therapy

Snake venoms are complex mixtures of biologically active polypeptides that target a variety of vital physiological functions in mammals. alpha-Neurotoxins, toxins that cause paralysis by binding to the nicotinic receptors at the postsynaptic region of the neuromuscular junction have been widely studied in terms of their structure-function relationships as well as gene structure, organization and expression. In this review, we describe the structure of alpha-neurotoxin genes and discuss their evolutionary relationships. Almost all members of neurotoxins have been found to exhibit a common evolutionary origin. The importance of alpha-neurotoxins in therapy and research has also been discussed to highlight their potential applications especially in the area of drug discovery.

Molecular cloning of phospholipases A(2) from venom glands of Echis carpet vipers

Venom toxin-specific antibodies offer a more rational treatment of snake envenoming than conventional antivenom. Here, we describe novel cDNAs encoding phospholipase A(2) (PLA(2)) isoforms from venom gland RNA of Echis pyramidum leakeyi (Epl), Echis sochureki (Es) and Echis ocellatus (Eo). The deduced amino acid sequences of these cDNAs encoded proteins with high overall sequence identity to the viper group II PLA(2) protein family, including the 14 cysteine residues capable of forming seven disulphide bonds that characterize this group of PLA(2) enzymes. Comparison of the PLA(2) sequences from Echis with those from related vipers failed to make significant geographic, taxonomic or PLA(2)-function distinctions between these Echis PLA(2) isoforms. However, their deduced hydrophilicity profiles revealed a conserved tertiary structure that we will exploit, by epidermal DNA immunization, to generate PLA(2)-neutralizing antibodies with polyspecific potential.

Modulation of Integrin-binding Selectivity by Mutation within the RGDLoop of Snake Venom Proteins: A Novel Drug Development Approach

Integrins are a family of heterodimeric class I transmembrane receptors, many of which bind to the RGD sequence in adhesive proteins and mediate the adhesive interactions of a variety of cells. The RGD motif has also been found in snake venom proteins that specifically inhibit integrin binding function and serve as potent integrin antagonists. The majority of these proteins interact with beta1 and beta3 associated integrins and their potency is at least 500-2000 times higher than short RGD peptides. Structural and functional studies suggest that the inhibitory potency of these proteins lies in subtle positional requirements of the tripeptide RGD that is harboured in a defined flexible loop. The integrin-binding specificity and selectivity of each of the proteins is controlled by amino acid residues in this loop in close vicinity to the RGD-motif. The review includes an overview of the structure and function of snake-venom integrin antagonists. The ability of these proteins to control platelet aggregation, cell adhesion and ligand binding is compared to that of short linear, cyclic RGD-peptides and RGD-containing proteins and the influence of modulation of amino acid residues flanking the RGD motif is also considered. The review is intended to provide insight into the development of novel inhibitors as drugs.