Alsophinase, a new P-III metalloproteinase with α-fibrinogenolytic and hemorrhagic activity from the venom of the rear-fanged Puerto Rican Racer Alsophis portoricensis (Serpentes: Dipsadidae)

Proteomic insight into the venom composition of the largest European rear-fanged snake, Malpolon monspessulanus monspessulanus

Snake envenomations constitute a worldwide neglected tropical disease, with the vast majority of lethal bites inflicted by front-fanged snakes from the viperid and elapid groups. Rear-fanged snakes (colubrids) were often considered harmless and as a result, are much less studied, but several documented deaths have suggested potent venom in this group as well. The largest European snake (Malpolon monspessulanus monspessulanus), known as the “Montpellier snake”, is such a rear-fanged snake that belongs to the Lamprophiidae family. Its venom remains largely unknown but cases of envenomation with neurological symptoms have been reported. Here, we provide the first insights into the composition of its venom using mass spectrometry methods. First, liquid chromatography coupled mass spectrometry analysis of the manually collected venom samples reveals a complex profile, with the majority of masses encompassing the range 500–3000 Da, 4000–8000 Da, and 10 000–30 000 Da. Next, shotgun proteomics allowed the identification of a total of 42 different known families of proteins, including snake venom metalloproteinases, peptidase M1, and cysteine-rich secretory proteins, as the most prominent. Interestingly, three-finger toxins were not detected, suggesting that neurotoxicity may occur via other, yet to be determined, toxin types. Overall, our results provide the basis for a better understanding of the effects of a peculiar snake venom on human symptomatology, but also on the main prey consumed by this species.

•

We investigate the venom composition of the largest European venomous snake.

•

LC-MS analysis of the crude manually collected venom revealed a complex profile.

•

Shotgun proteomic analysis identified 42 different protein families.

•

Major components include SVMPs, consistent with the clinical features.

Protease Activity Profiling of Snake Venoms Using High-Throughput Peptide Screening

Snake venom metalloproteinases (SVMPs) and snake venom serine proteinases (SVSPs) are among the most abundant enzymes in many snake venoms, particularly among viperids. These proteinases are responsible for some of the clinical manifestations classically seen in viperid envenomings, including hemorrhage, necrosis, and coagulopathies. The objective of this study was to investigate the enzymatic activities of these proteins using a high-throughput peptide library to screen for the proteinase targets of the venoms of five viperid (Echis carinatus, Bothrops asper, Daboia russelii, Bitis arietans, Bitis gabonica) and one elapid (Naja nigricollis) species of high medical importance. The proteinase activities of these venoms were each tested against 360 peptide substrates, yielding 2160 activity profiles. A nonlinear regression model that accurately described the observed enzymatic activities was fitted to the experimental data, allowing for the comparison of cleavage rates across species. In this study, previously unknown protein targets of snake venom proteinases were identified, potentially implicating novel human and animal proteins that may be involved in the pathophysiology of viper envenomings. The functional relevance of these targets was further evaluated and discussed. These new findings may contribute to our understanding of the clinical manifestations and underlying biochemical mechanisms of snakebite envenoming by viperid species.

Biochemical characterization of venom from Pseudoboa neuwiedii (Neuwied's false boa; Xenodontinae; Pseudoboini)

In this work, we examined the proteolytic and phospholipase A₂ (PLA₂) activities of venom from the opisthoglyphous colubrid Pseudoboa neuwiedii. Proteolytic activity (3 and 10 μg of venom) was comparable to that of Bothrops neuwiedii venom but less than Bothrops atrox. This activity was inhibited by EDTA and 1,10-phenanthroline but only slightly affected (≤30% inhibition) by PMSF and AEBSF, indicating it was mediated by snake venom metalloproteinases (SVMPs). The pH and temperature optima for proteolytic activity were 8.0 and 37 °C, respectively. The venom had no esterase activity, whereas PLA₂ activity was similar to B. atrox, greater than B. neuwiedii but less than B. jararacussu. SDS-PAGE revealed venom proteins >100 kDa, 45-70 kDa, 21-24 kDa and ~15 kDa, and mass spectrometry of protein bands revealed SVMPs, cysteine-rich secretory proteins (CRISPs) and PLA₂, but no serine proteinases. In gelatin zymography, the most active bands occurred at 65-68 kDa (seen with 0.05-0.25 μg of venom). Caseinolytic activity occurred at 50-66 kDa and was generally weaker than gelatinolytic activity. RP-HPLC of venom yielded 15 peaks, five of which showed gelatinolytic activity; peak 7 was the most active and apparently contained a P-III class SVMP. The venom showed α-fibrinogenase activity, without affecting the β and γ chains; this activity was inhibited by EDTA and 1,10-phenanthroline. The venom did not clot rat citrated plasma but reduced the rate and extent of coagulation after plasma recalcification. In conclusion, P. neuwiedii venom is highly proteolytic and could potentially affect coagulation in vivo by degrading fibrinogen via SVMPs.

Transcriptome-facilitated proteomic characterization of rear-fanged snake venoms reveal abundant metalloproteinases with enhanced activity

High-throughput technologies were used to identify venom gland toxin expression and to characterize the venom proteomes of two rear-fanged snakes, Ahaetulla prasina (Asian Green Vine Snake) and Borikenophis portoricensis (Puerto Rican Racer). Sixty-nine complete toxin-coding transcripts from 12 venom protein superfamilies (A. prasina) and 50 complete coding transcripts from 11 venom protein superfamilies (B. portoricensis) were identified in the venom glands. However, only 18% (A. prasina) and 32% (B. portoricensis) of the translated protein isoforms were detected in the proteome of these venoms. Both venom gland transcriptomes and venom proteomes were dominated by P-III metalloproteinases. Three-finger toxins, cysteine-rich secretory proteins, and C-type lectins were present in moderate amounts, but other protein superfamilies showed very low abundances. Venoms contained metalloproteinase activity comparable to viperid snake venom levels, but other common venom enzymes were absent or present at negligible levels. Western blot analysis showed metalloproteinase and cysteine-rich secretory protein epitopes shared with the highly venomous Boomslang (Dispholidus typus). The abundance of metalloproteinases emphasizes the important trophic role of these toxins. Comprehensive, transcriptome-informed definition of proteomes and functional characterization of venom proteins in rear-fanged snake families help to elucidate toxin evolution and provide models for protein structure-function analyses.

Targeting Metastasis with Snake Toxins: Molecular Mechanisms

Metastasis involves the migration of cancer cells from a primary tumor to invade and establish secondary tumors in distant organs, and it is the main cause for cancer-related deaths. Currently, the conventional cytostatic drugs target the proliferation of malignant cells, being ineffective in metastatic disease. This highlights the need to find new anti-metastatic drugs. Toxins isolated from snake venoms are a natural source of potentially useful molecular scaffolds to obtain agents with anti-migratory and anti-invasive effects in cancer cells. While there is greater evidence concerning the mechanisms of cell death induction of several snake toxin classes on cancer cells; only a reduced number of toxin classes have been reported on (i.e., disintegrins/disintegrin-like proteins, C-type lectin-like proteins, C-type lectins, serinproteases, cardiotoxins, snake venom cystatins) as inhibitors of adhesion, migration, and invasion of cancer cells. Here, we discuss the anti-metastatic mechanisms of snake toxins, distinguishing three targets, which involve (1) inhibition of extracellular matrix components-dependent adhesion and migration, (2) inhibition of epithelial-mesenchymal transition, and (3) inhibition of migration by alterations in the actin/cytoskeleton network.

Edema and Nociception Induced by Philodryas patagoniensis Venom in Mice: A Pharmacological Evaluation with Implications for the Accident Treatment

We have investigated the mechanisms involved in the genesis of edema and nociception induced by Philodryas patagoniensis venom (PpV) injected into the footpad of mice. PpV induced dose-related edema and nociceptive effects. Pretreatment of mice with cyclooxygenase inhibitor (indomethacin), but not with cyclooxygenase 2 inhibitor (celecoxib) markedly inhibited both effects. Pretreatments with H₁ receptor antagonist (promethazine) or with dual histamine-serotonin inhibitor (cyproheptadine) failed in inhibiting both effects. In groups pretreated with captopril (angiotensin-converting enzyme inhibitor) the edema was unaltered, but nociception was clearly increased, suggesting the participation of kinins in the pathophysiology of the nociception but not of the edema-forming effect of PpV. When PpV was treated with EDTA, the nociception was similar to the one induced by untreated venom, but edema was markedly reduced. We concluded that PpV-induced edema and nociception have cyclooxygenase eicosanoids as the main mediators and no participation of vasoactive amines. Kinins seem to participate in nociception but not in edema induced by PpV. The results also suggest that metalloproteinases are the main compounds responsible for the edema, but not for the nociception induced by this venom.

Understanding Biological Roles of Venoms Among the Caenophidia: The Importance of Rear-Fanged Snakes

Snake venoms represent an adaptive trophic response to the challenges confronting a limbless predator for overcoming combative prey, and this chemical means of subduing prey shows several dominant phenotypes. Many front-fanged snakes, particularly vipers, feed on various vertebrate and invertebrate prey species, and some of their venom components (e.g., metalloproteinases, cobratoxin) appear to have been selected for "broad-brush" incapacitation of different prey taxa. Using proteomic and genomic techniques, the compositional diversity of front-fanged snakes is becoming well characterized; however, this is not the case for most rear-fanged colubroid snakes. Because these species consume a high diversity of prey, and because venoms are primarily a trophic adaptation, important clues for understanding specific selective pressures favoring venom component composition will be found among rear-fanged snake venoms. Rear-fanged snakes typically (but not always) produce venoms with lower complexity than front-fanged snakes, and there are even fewer dominant (and, arguably, biologically most relevant) venom protein families. We have demonstrated taxon-specific toxic effects, where lizards and birds show high susceptibility while mammals are largely unaffected, for both Old World and New World rear-fanged snakes, strongly indicating a causal link between toxin evolution and prey preference. New data are presented on myotoxin a, showing that the extremely rapid paralysis induced by this rattlesnake toxin is specific for rodents, and that myotoxin a is ineffectual against lizards. Relatively few rear-fanged snake venoms have been characterized, and basic natural history data are largely lacking, but directed sampling of specialized species indicates that novel compounds are likely among these specialists, particularly among those species feeding on invertebrate prey such as scorpions and centipedes. Because many of the more than 2200 species of colubroid snakes are rear-fanged, and many possess a Duvernoy's venom gland, understanding the nature of their venoms is foundational to understanding venom evolution in advanced snakes.

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.

Full-Length Venom Protein cDNA Sequences from Venom-Derived mRNA: Exploring Compositional Variation and Adaptive Multigene Evolution

Envenomation of humans by snakes is a complex and continuously evolving medical emergency, and treatment is made that much more difficult by the diverse biochemical composition of many venoms. Venomous snakes and their venoms also provide models for the study of molecular evolutionary processes leading to adaptation and genotype-phenotype relationships. To compare venom complexity and protein sequences, venom gland transcriptomes are assembled, which usually requires the sacrifice of snakes for tissue. However, toxin transcripts are also present in venoms, offering the possibility of obtaining cDNA sequences directly from venom. This study provides evidence that unknown full-length venom protein transcripts can be obtained from the venoms of multiple species from all major venomous snake families. These unknown venom protein cDNAs are obtained by the use of primers designed from conserved signal peptide sequences within each venom protein superfamily. This technique was used to assemble a partial venom gland transcriptome for the Middle American Rattlesnake (Crotalus simus tzabcan) by amplifying sequences for phospholipases A₂, serine proteases, C-lectins, and metalloproteinases from within venom. Phospholipase A₂ sequences were also recovered from the venoms of several rattlesnakes and an elapid snake (Pseudechis porphyriacus), and three-finger toxin sequences were recovered from multiple rear-fanged snake species, demonstrating that the three major clades of advanced snakes (Elapidae, Viperidae, Colubridae) have stable mRNA present in their venoms. These cDNA sequences from venom were then used to explore potential activities derived from protein sequence similarities and evolutionary histories within these large multigene superfamilies. Venom-derived sequences can also be used to aid in characterizing venoms that lack proteomic profiles and identify sequence characteristics indicating specific envenomation profiles. This approach, requiring only venom, provides access to cDNA sequences in the absence of living specimens, even from commercial venom sources, to evaluate important regional differences in venom composition and to study snake venom protein evolution.

This work demonstrates that full-length venom protein messenger RNAs are present in secreted venoms and can be used to acquire full-length protein sequences of toxins from both front-fanged (Elapidae, Viperidae) and rear-fanged (Colubridae) snake venoms, eliminating the need to use venom glands. Full-length transcripts were obtained from venom samples that were fresh, newly lyophilized, old, field desiccated or commercially prepared, representing a significant advance over previous attempts which produced only partial sequence transcripts. Transcripts for all major venom protein families (metalloproteinases, serine proteases, C-type lectins, phospholipases A₂ and three-finger toxins) responsible for clinically significant snakebite symptoms were obtained from venoms. These sequences aid in the identification and characterization of venom proteome profiles, allowing for the identification of peptide sequences, specific isoforms, and novel venom proteins. The application of this technique will help to provide venom protein sequences for many snake species, including understudied rear-fanged snakes. Venom protein transcripts offer important insights into potential snakebite envenomation profiles and the molecular evolution of venom protein multigene families. By requiring only venom to obtain venom protein cDNAs, the approach detailed here will provide access to cDNA-based protein sequences from commercial and other venom sources, facilitating study of snake venom protein composition and evolution.

Ixodes scapularis Tick Saliva Proteins Sequentially Secreted Every 24 h during Blood Feeding

Ixodes scapularis is the most medically important tick species and transmits five of the 14 reportable human tick borne disease (TBD) agents in the USA. This study describes LC-MS/MS identification of 582 tick- and 83 rabbit proteins in saliva of I. scapularis ticks that fed for 24, 48, 72, 96, and 120 h, as well as engorged but not detached (BD), and spontaneously detached (SD). The 582 tick proteins include proteases (5.7%), protease inhibitors (7.4%), unknown function proteins (22%), immunity/antimicrobial (2.6%), lipocalin (3.1%), heme/iron binding (2.6%), extracellular matrix/ cell adhesion (2.2%), oxidant metabolism/ detoxification (6%), transporter/ receptor related (3.2%), cytoskeletal (5.5%), and housekeeping-like (39.7%). Notable observations include: (i) tick saliva proteins of unknown function accounting for >33% of total protein content, (ii) 79% of proteases are metalloproteases, (iii) 13% (76/582) of proteins in this study were found in saliva of other tick species and, (iv) ticks apparently selectively inject functionally similar but unique proteins every 24 h, which we speculate is the tick's antigenic variation equivalent strategy to protect important tick feeding functions from host immune system. The host immune responses to proteins present in 24 h I. scapularis saliva will not be effective at later feeding stages. Rabbit proteins identified in our study suggest the tick's strategic use of host proteins to modulate the feeding site. Notably fibrinogen, which is central to blood clotting and wound healing, was detected in high abundance in BD and SD saliva, when the tick is preparing to terminate feeding and detach from the host. A remarkable tick adaptation is that the feeding lesion is completely healed when the tick detaches from the host. Does the tick concentrate fibrinogen at the feeding site to aide in promoting healing of the feeding lesion? Overall, these data provide broad insight into molecular mechanisms regulating different tick feeding phases. These data set the foundation for in depth I. scapularis tick feeding physiology and TBD transmission studies.

Discovery of toxin-encoding genes from the false viper Macropisthodon rudis, a rear-fanged snake, by transcriptome analysis of venom gland

Although rear-fanged snakes are often considered as non-threatening to humans, some species are lethal or medically hazardous. The toxin components and bioactivities of front-fanged snakes have been extensively studied; however, only limited research has explored the venoms of rear-fanged snakes. The false viper, Macropisthodon rudis, is widespread in southern China, but little is known about the toxins that this snake produces. Here, we analyzed the transcriptome of the venom gland of M. rudis using high-throughput sequencing with an illumina HiSeq 2000. The raw data were assembled and annotated using public databases. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways and gene ontology (GO) were analyzed. Using sequence comparisons, snake venom metalloproteinases (SVMPs) and a phosphodiesterase (PDE) were discovered in the venom gland of M. rudis.

The pro-coagulant fibrinogenolytic serine protease isoenzymes purified from Daboia russelii russelii venom coagulate the blood through factor V activation: role of glycosylation on enzymatic activity

Proteases from Russell's viper venom (RVV) induce a variety of toxic effects in victim. Therefore, four new RVV protease isoenzymes of molecular mass 32901.044 Da, 333631.179 Da, 333571.472 Da, and 34594.776 Da, were characterized in this study. The first 10 N-terminal residues of these serine protease isoenzymes showed significant sequence homology with N-terminal sequences of snake venom thrombin-like and factor V-activating serine proteases, which was reconfirmed by peptide mass fingerprinting analysis. These proteases were found to be different from previously reported factor V activators isolated from snake venoms. These proteases showed significantly different fibrinogenolytic, BAEE-esterase and plasma clotting activities but no fibrinolytic, TAME-esterase or amidolytic activity against the chromogenic substrate for trypsin, thrombin, plasmin and factor Xa. Their Km and Vmax values towards fibrinogen were determined in the range of 6.6 to 10.5 µM and 111.0 to 125.5 units/mg protein, respectively. On the basis of fibrinogen degradation pattern, they may be classified as A/B serine proteases isolated from snake venom. These proteases contain ∼ 42% to 44% of N-linked carbohydrates by mass whereas partially deglycosylated enzymes showed significantly less catalytic activity as compared to native enzymes. In vitro these protease isoenzymes induce blood coagulation through factor V activation, whereas in vivo they provoke dose-dependent defibrinogenation and anticoagulant activity in the mouse model. At a dose of 5 mg/kg, none of these protease isoenzymes were found to be lethal in mice or house geckos, suggesting therapeutic application of these anticoagulant peptides for the prevention of thrombosis.

Hemorrhagin VaH4, a covalent heterodimeric P-III metalloproteinase from Vipera ammodytes ammodytes with a potential antitumour activity

In the envenomation caused by a bite of Vipera ammodytes ammodytes, the most venomous snake in Europe, hemorrhage is usually the most severe consequence in man. Identifying and understanding the hemorrhagic components of its venom is therefore particularly important in optimizing medical treatment of patients. We describe a novel high molecular mass hemorrhagin, VaH4. The isolated molecule is a covalent dimer of two homologous subunits, VaH4-A and VaH4-B. Complete structural characterization of A and partial characterization of B revealed that both belong to the P-III class of snake venom metalloproteinases (SVMPs), comprising a metalloproteinase, a disintegrin-like domain and a cysteine-rich domain. However, neither VaH4-A nor VaH4-B possess the Cys174 involved in the inter-subunit disulphide bond of P-III SVMPs. A three-dimensional model of the VaH4 dimer suggests that Cys132 serves this function. This implies that dimers in the P-III class of SVMPs can be formed either between their Cys132 or Cys174 residues. The proteolytic activity and stability of VaH4 depend on Zn²⁺ and Ca²⁺ ions and the presence of glycosaminoglycans, which indicates physiological interaction of VaH4 with the latter element of the extracellular matrix (ECM). The molecular mass of VaH4, determined by MALDI/TOF mass spectrometry, is 110.2 kDa. N-deglycosylation reduced the mass of each monomer by 8.7 kDa. The two possible N-glycosylation sites in VaH4-A are located at completely different positions from those in homodimeric P-IIIc VaH3 from the same venom, however, without any evident functional implications. The hemorrhagic activity of this slightly acidic SVMP is ascribed to its hydrolysis of components of the ECM, particularly fibronectin and nidogen, and of some blood coagulation proteins, in particular the α-chain of fibrinogen. VaH4 is also significant medically as we found it cytotoxic against cancer cells and due to its substantial sequence similarity to ADAM/ADAMTS family of physiologically very important human proteins of therapeutic potential.

Biochemical and biological analysis of Philodryas baroni (Baron’s Green Racer; Dipsadidae) venom

Philodryas baroni—an attractively colored snake—has become readily available through the exotic pet trade. Most people consider this species harmless; however, it has already caused human envenomation. As little is known about the venom from this South American opisthoglyphous “colubrid” snake, herein, we studied its protein composition by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE), as well as its effects on the hemostatic system. Both reducing and nonreducing SDS-PAGE analysis demonstrated that the venom exhibits greatest complexity in the range of 50–80 kDa. The venom displayed proteolytic activity toward azocollagen, with a specific activity of 75.5 U mg−1, and rapidly hydrolyzed the Aα-chain of fibrinogen, exhibiting lower activity toward the Bβ- and γ-chains. The venom from P. baroni showed no platelet proaggregating activity per se, but it inhibited collagen- and thrombin-induced platelet aggregation. Prominent hemorrhage developed in mouse skin after intradermal injection of the crude venom, and its minimum hemorrhagic dose was 13.9 μg. When injected intramuscularly into the gastrocnemius of mice, the venom induced local effects such as hemorrhage, myonecrosis, edema, and leucocyte infiltration. Due to its venom toxicity shown herein, P. baroni should be considered dangerous to humans and any medically significant bite should be promptly reviewed by a qualified health professional.

Biochemical and pharmacological properties of a new thrombin-like serine protease (Russelobin) from the venom of Russell's Viper (Daboia russelii russelii) and assessment of its therapeutic potential

BACKGROUND

Snake venoms are rich sources of bioactive molecules, and several venom-derived proteins have entered clinical trials for use in ischemic disorders; however, late-stage failure of a recent drug candidate due to low in vivo efficacy demonstrated the need for new sources of fibrinogenolytic drug candidates.

METHODS

A 51.3kDa thrombin-like serine protease (Russelobin) purified from the venom of Russell's Viper (Daboia russelii russelii) was subjected to extensive biochemical characterization, including N-terminal sequencing, substrate specificity, kinetic and inhibitor assays, glycosylation analysis and stability assays. Toxicity and pathology analyses were conducted in NSA mice.

RESULTS

Russelobin has extensive N-terminus identity with a beta-fibrinogenase-like serine proteinase precursor from Daboia russelii siamensis venom, a mass of 51.3kDa and contains extensive N-linked oligosaccharides. Serine protease inhibitors and heparin significantly decreased activity, with much lower inhibition by DTT, antithrombin-III and α2-macroglobulin. Russelobin preferentially released FPA and slowly released FPB from human fibrinogen, forming a labile fibrin clot readily hydrolyzed by plasmin. The partially deglycosylated enzyme showed significantly lower activity toward fibrinogen and less resistance against neutralization by plasma α2MG and antithrombin-III. Russelobin was non-cytotoxic, non-lethal and produced no histopathologies in mice, and it demonstrated in vivo dose-dependent defibrinogenating activity.

CONCLUSIONS

Russelobin is an A/B fibrinogenase with high specificity toward fibrinogen, both in vitro and in vivo. Extensive glycosylation appears to protect the molecule against endogenous protease inhibitors, prolonging its in vivo efficacy.

GENERAL SIGNIFICANCE

Due to its low toxicity, stability and activity as a defibrinogenating agent, Russelobin shows high potential for cardiovascular drug development.

Molecular basis for prey relocation in viperid snakes

BACKGROUND

Vertebrate predators use a broad arsenal of behaviors and weaponry for overcoming fractious and potentially dangerous prey. A unique array of predatory strategies occur among snakes, ranging from mechanical modes of constriction and jaw-holding in non-venomous snakes, to a chemical means, venom, for quickly dispatching prey. However, even among venomous snakes, different prey handling strategies are utilized, varying from the strike-and-hold behaviors exhibited by highly toxic elapid snakes to the rapid strike-and-release envenomation seen in viperid snakes. For vipers, this mode of envenomation represents a minimal risk predatory strategy by permitting little contact with or retaliation from prey, but it adds the additional task of relocating envenomated prey which has wandered from the attack site. This task is further confounded by trails of other unstruck conspecific or heterospecific prey. Despite decades of behavioral study, researchers still do not know the molecular mechanism which allows for prey relocation.

RESULTS

During behavioral discrimination trials (vomeronasal responsiveness) to euthanized mice injected with size-fractionated venom, Crotalus atrox responded significantly to only one protein peak. Assays for enzymes common in rattlesnake venoms, such as exonuclease, L-amino acid oxidase, metalloproteinase, thrombin-like and kallikrein-like serine proteases and phospholipase A(2), showed that vomeronasal responsiveness was not dependent on enzymatic activity. Using mass spectrometry and N-terminal sequencing, we identified the proteins responsible for envenomated prey discrimination as the non-enzymatic disintegrins crotatroxin 1 and 2. Our results demonstrate a novel and critical biological role for venom disintegrins far beyond their well-established role in disruption of cell-cell and cell-extracellular matrix interactions.

CONCLUSIONS

These findings reveal the evolutionary significance of free disintegrins in venoms as the molecular mechanism in vipers allowing for effective relocation of envenomated prey. The presence of free disintegrins in turn has led to evolution of a major behavioral adaptation (strike-and-release), characteristic of only rattlesnakes and other vipers, which exploits and refines the efficiency of a pre-existing chemical means of predation and a highly sensitive olfaction system. This system of a predator chemically tagging prey represents a novel trend in the coevolution of predator-prey relationships.

Non-front-fanged colubroid snakes: a current evidence-based analysis of medical significance

Non-front-fanged colubroid snakes (NFFC; formerly and artificially taxonomically assembled as "colubrids") comprise about 70% of extant snake species and include several taxa now known to cause lethal or life threatening envenoming in humans. Although the medical risks of bites by only a handful of species have been documented, a growing number of NFFC are implicated in medically significant bites. The majority of these snakes have oral products (Duvernoy's secretions, or venoms) with unknown biomedical properties and their potential for causing harm in humans is unknown. Increasingly, multiple NFFC species are entering the commercial snake trade posing an uncertain risk. Published case reports describing NFFC bites were assessed for evidence-based value, clinical detail and verified species identification. These data were subjected to meta-analysis and a hazard index was generated for select taxa. Cases on which we consulted or personally treated were included and subjected to the same assessment criteria. Cases involving approximately 120 species met the selection criteria, and a small subset designated Hazard Level 1 (most hazardous), contained 5 species with lethal potential. Recommended management of these cases included antivenom for 3 species, Dispholidus typus, Rhabdophis tiginis, Rhabdophis subminiatus, whereas others in this subset without commercially available antivenoms (Thelotornis spp.) were treated with plasma/erythrocyte replacement therapy and supportive care. Heparin, antifibrinolytics and/or plasmapheresis/exchange transfusion have been used in the management of some Hazard Level 1 envenomings, but evidence-based analysis positively contraindicates the use of any of these interventions. Hazard Level 2/3 species were involved in cases containing mixed quality data that implicated these taxa (e.g. Boiga irregularis, Philodryas olfersii, Malpolon monspessulanus) with bites that caused rare systemic effects. Recommended management may include use of acetylcholinesterase inhibitors (e.g. neostigmine) and wound care on a case-by-case basis. Hazard level 3 species comprised a larger group capable of producing significant local effects only, often associated with a protracted bite (eg Heterodon nasicus, Borikenophis (Alsophis) portoricensis, Platyceps (Coluber) rhodorachis). Management is restricted to wound care. Bites by Hazard level 4 species comprised the majority of surveyed taxa and these showed only minor effects of no clinical importance. This study has produced a comprehensive evidence-based listing of NFFC snakes tabulated against medical significance of bites, together with best-practice management recommendations. This analysis assumes increasing importance, as there is growing exposure to lesser-known NFFC snakes, particularly in captive collections that may uncover further species of significance in the future. Careful and accurate documentation of bites by verified species of NFFC snakes is required to increase the evidence base and establish the best medical management approach for each species.

Differential evolution and neofunctionalization of snake venom metalloprotease domains

Snake venom metalloproteases (SVMP) are composed of five domains: signal peptide, propeptide, metalloprotease, disintegrin, and cysteine-rich. Secreted toxins are typically combinatorial variations of the latter three domains. The SVMP-encoding genes of Psammophis mossambicus venom are unique in containing only the signal and propeptide domains. We show that the Psammophis SVMP propeptide evolves rapidly and is subject to a high degree of positive selection. Unlike Psammophis, some species of Echis express both the typical multidomain and the unusual monodomain (propeptide only) SVMP, with the result that a lower level of variation is exerted upon the latter. We showed that most mutations in the multidomain Echis SVMP occurred in the protease domain responsible for proteolytic and hemorrhagic activities. The cysteine-rich and disintegrin-like domains, which are putatively responsible for making the P-III SVMPs more potent than the P-I and P-II forms, accumulate the remaining variation. Thus, the binding sites on the molecule's surface are evolving rapidly whereas the core remains relatively conserved. Bioassays conducted on two post-translationally cleaved novel proline-rich peptides from the P. mossambicus propeptide domain showed them to have been neofunctionalized for specific inhibition of mammalian a7 neuronal nicotinic acetylcholine receptors. We show that the proline rich postsynaptic specific neurotoxic peptides from Azemiops feae are the result of convergent evolution within the precursor region of the C-type natriuretic peptide instead of the SVMP. The results of this study reinforce the value of studying obscure venoms for biodiscovery of novel investigational ligands.

Venom proteomes of South and North American opisthoglyphous (Colubridae and Dipsadidae) snake species: a preliminary approach to understanding their biological roles

Opisthoglyphous snake venoms remain under-explored despite being promising sources for ecological, evolutionary and biomedical/biotechnological research. Herein, we compared the protein composition and enzymatic properties of the venoms of Philodryas baroni (PbV), Philodryas olfersii olfersii (PooV) and Philodryas patagoniensis (PpV) from South America, and Hypsiglena torquata texana (HttV) and Trimorphodon biscutatus lambda (TblV) from North America. All venoms degraded azocasein, and this metalloproteinase activity was significantly inhibited by EDTA. PooV exhibited the highest level of catalytic activity towards synthetic substrates for serine proteinases. All venoms hydrolyzed acetylthiocholine at low levels, and only TblV showed phospholipase A(2) activity. 1D and 2D SDS-PAGE profile comparisons demonstrated species-specific components as well as several shared components. Size exclusion chromatograms from the three Philodryas venoms and HttV were similar, but TblV showed a notably different pattern. MALDI-TOF MS of crude venoms revealed as many as 49 distinct protein masses, assigned to six protein families. MALDI-TOF/TOF MS analysis of tryptic peptides confirmed the presence of cysteine-rich secretory proteins in all venoms, as well as a phospholipase A(2) and a three-finger toxin in TblV. Broad patterns of protein composition appear to follow phylogenetic lines, with finer scale variation likely influenced by ecological factors such as diet and habitat.