Characterization and molecular cloning of neurotoxic phospholipases A2 from Taiwan viper (Vipera russelli formosensis)

Proteome analysis of Daboia russelii venom, a medically important snake from the Indian sub-continent

Daboia russelii is a category-I medically important snake throughout the Indian sub-continent contributing to majority of snakebite incidences in this part of the world. As such, extensive studies on its venom composition and search of efficient and appropriate interventions for its treatment become crucial. In this study, the proteome of Daboia russelii venom from Tanore, Rajshahi, Bangladesh was profiled using a combination of chromatographic and mass spectrometric techniques. A total of 37 different proteins belonging to 11 different snake venom protein families were detected. Proteomics analysis revealed the presence of major phospholipase A2 toxins. Daboiatoxin (both A and B subunits), the main lethal PLA2 toxin in the venom of Daboia siamensis (Myanmar viper) which is neurotoxic, myotoxic and cytotoxic was detected. Presence of Daboxin P, which is a major protein in the venom of Indian Daboia russelii with strong anticoagulant activity, was also observed. Inconsistent distribution of such lethal toxins in the venom of same species calls for more investigations of snake venoms from lesser explored regions and formulation of better alternatives to the current antivenom therapy for efficient treatment.

In Vitro Efficacy of Antivenom and Varespladib in Neutralising Chinese Russell's Viper (Daboia siamensis) Venom Toxicity

The venom of the Russell's viper (Daboia siamensis) contains neurotoxic and myotoxic phospholipase A₂ toxins which can cause irreversible damage to motor nerve terminals. Due to the time delay between envenoming and antivenom administration, antivenoms may have limited efficacy against some of these venom components. Hence, there is a need for adjunct treatments to circumvent these limitations. In this study, we examined the efficacy of Chinese D. siamensis antivenom alone, and in combination with a PLA₂ inhibitor, Varespladib, in reversing the in vitro neuromuscular blockade in the chick biventer cervicis nerve-muscle preparation. Pre-synaptic neurotoxicity and myotoxicity were not reversed by the addition of Chinese D. siamensis antivenom 30 or 60 min after venom (10 µg/mL). The prior addition of Varespladib prevented the neurotoxic and myotoxic activity of venom (10 µg/mL) and was also able to prevent further reductions in neuromuscular block and muscle twitches when added 60 min after venom. The addition of the combination of Varespladib and antivenom 60 min after venom failed to produce further improvements than Varespladib alone. This demonstrates that the window of time in which antivenom remains effective is relatively short compared to Varespladib and small-molecule inhibitors may be effective in abrogating some activities of Chinese D. siamensis venom.

In Vitro Toxicity of Chinese Russell’s Viper (Daboia siamensis) Venom and Neutralisation by Antivenoms

Daboia siamensis (Russell’s viper) is a highly venomous and medically important snake in China, as well as much of Asia. There is minimal information on the pharmacological activity of the venom of the Chinese species, and currently no commercially available specific antivenom in China. This has led to the use of non-specific antivenoms to treat D. siamensis envenomation. In this study, the in vitro neurotoxicity and myotoxicity of D. siamensis venom was examined and the efficacy of four antivenoms was investigated, including the recently developed Chinese D. siamensis monovalent antivenom (C-DsMAV) and three commercially available antivenoms (Thai D. siamensis (Thai-DsMAV) monovalent antivenom, Deinagkistrodon acutus monovalent antivenom (DaAV), and Gloydius brevicaudus monovalent antivenom (GbAV). D. siamensis venom (10–30 µg/mL) caused the concentration-dependent inhibition of indirect twitches in the chick biventer cervicis nerve muscle preparation, without abolishing contractile responses to exogenous agonists ACh or CCh, indicating pre-synaptic neurotoxicity. Myotoxicity was also evident at these concentrations with inhibition of direct twitches, an increase in baseline tension, and the partial inhibition of ACh, CCh, and KCl responses. The prior addition of C-DsMAV or Thai-DsMAV prevented the neurotoxic and myotoxic activity of D. siamensis venom (10 µg/mL). The addition of non-specific antivenoms (GbAV and DaAV) partially prevented the neurotoxic activity of venom (10 µg/mL) but failed to neutralize the myotoxic effects. We have shown that D. siamensis venom exhibits in vitro weak presynaptic neurotoxicity and myotoxicity, which can be prevented by the pre-addition of the Chinese and Thai Russell’s viper antivenoms. Non-specific antivenoms were poorly efficacious. There should be further development of a monospecific antivenom against D. siamensis envenomation in China.

Proteomics and antivenom immunoprofiling of Russell's viper (Daboia siamensis) venoms from Thailand and Indonesia

The Eastern Russell’s viper, Daboia siamensis, is a WHO Category 1 medically important venomous snake. It has a wide but disjunct distribution in Southeast Asia. The specific antivenom, D. siamensis Monovalent Antivenom (DsMAV-Thailand) is produced in Thailand but not available in Indonesia, where a heterologous trivalent antivenom, Serum Anti Bisa Ular (SABU), is used instead. This study aimed to investigate the geographical venom variation of D. siamensis from Thailand (Ds-Thailand) and Indonesia (Ds-Indonesia), and the immunorecognition of the venom proteins by antivenoms.

Complementary DNA library of Myanmar Russell's viper (Daboia russelii siamensis) venom gland

Geographical variations of snake venoms of the same species are well-known. Exploring the components of venom from each region will give insights in its distinctive toxicities. Venom gland cDNA library of Russell's viper (RV) from Myanmar (Daboia russelii siamensis) was constructed to create a catalog of expressed sequences tags (ESTs) and to compare with sequences from RV of other countries. The cDNA library of venom gland was generated by using CloneMiner™ II cDNA Library Construction Kit. Clones were subjected to Sanger sequencing and analyses by bioinformatics tools. From 251 isolated clones, 38 ESTs were assembled into 6 clusters and 21 singlets. Toxin sequences contributed to 57.9% of all transcripts and Kunitz-type serine protease inhibitors are most abundant (45.5% of toxin transcripts). The Myanmar RV phospholipase A2 (PLA2) showed 98% and 74% identity to D. r. russelii PLA2 from India (DrK-bI) and PLA2 of D. r. siamensis from Thailand as well as Taiwan, respectively. The cysteine-rich secretory protein (CRISP) homologs from Myanmar RV were first identified here showing homology to CRISP from Taiwan RV and European vipers with 98% and 90% identity, respectively. The RV 5' nucleotidase was also first cloned. In summary, Myanmar RV showed a unique gene expression pattern and sequences. Large scale analysis by next-generation sequencing is warranted.

Twelve month prospective study of snakebite in a major teaching hospital in Mandalay, Myanmar; Myanmar Snakebite Project (MSP)

The Myanmar Snakebite Project is an Australian government (Department of Foreign Affairs and Trade) supported foreign aid project in collaboration with the Myanmar government with the aim of improving outcomes for snakebite patients in Myanmar. As part of the project a case record database was established to document prospective cases of snakebite presenting to Mandalay General Hospital, in Upper Myanmar. The study period was 12 months (1-2-2016 to 31-1-2017). Snake identity was based on a mixture of identified dead snakes brought with patients, doctor's clinical opinion and patient identification. 965 patients were enrolled during the 12 month period, of whom 948 were included for analysis. The male: female ratio was 1.58:1. Most cases involved bites to the lower limbs (82.5%) and adults involved in farm work, confirming snakebite as an occupational disease in this community. Motorised transport was by far the most common form of transport to health care and most patients sought care from the health system (87.7%), not traditional healers (11.5%) as their first point of contact. The officially promoted application of a pressure pad, bandage and immobilisation as first aid for snakebite was almost never used, while most patients used some form of tourniquet (92.0%). 85.4% of cases where a snake ID was listed were bitten by Russell's vipers. Russell's viper bites were responsible for all fatalities (9.8% of cases) and all cases of Acute Kidney Injury (AKI). For all cases, clinical features included local swelling (76.5%), local pain (62.6%), AKI (59.8%), incoagulable blood (57.9%), regional lymphadenopathy (39.8%), nausea/vomiting (40.4%), thrombocytopenia (53.6%), abdominal pain (28.8%), shock (11.8%), secondary infection (8.6%), panhypopituitarism (2.1%). AKI required renal replacement therapy (RRT) in 23.9% of cases, all ascribed to Russell's viper bite. Green pit viper bites were the next most common cause of bites (7.6%) and were associated with incoagulable blood (29%) and occasionally shock (5%) and local necrosis (3%), and in one case AKI not requiring RRT. In contrast to Russell's viper bites, green pit viper bite was most likely to occur in the home (49%). Some green pit viper patients were treated with Russell's viper antivenom (15%), presumably because they had incoagulable blood, although this antivenom is not effective against green pit viper envenoming. For the entire patient group, antivenom was given in 80.5% of cases. The most common indications were presence of coagulopathy/non-clotting blood (59.8%), local swelling (47.4%), oliguria/anuria (19.8%), heavy proteinuria (19.4%). A febrile reaction to antivenom was reported in 47.9% of cases, while anaphylaxis, occurred in 7.9% of cases.

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Reports 12 month prospective observational study of snakebite patients at Mandalay General Hosp.

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Snakebite was an occupational disease of farm workers, tourniquets the most common first aid.

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Russell's viper (RV) responsible for most bites, causing coagulopathy, thrombocytopenia, AKI.

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Green pit viper bites were the next most common, potentially causing diagnostic confusion with RV.

Translational Venomics: Third-Generation Antivenomics of Anti-Siamese Russell's Viper, Daboia siamensis, Antivenom Manufactured in Taiwan CDC's Vaccine Center

The venom proteome of Siamese Russell’s viper from Taiwan, alongside complementary in vivo lethality neutralization assay and in vitro third-generation antivenomics assessment of the preclinical efficacy of the homologous antivenom manufactured in Taiwan CDC’s Vaccine Center, are here reported. Taiwanese Russell’s viper venom proteome comprised 25 distinct gene products, with the heterodimeric PLA₂ viperotoxin-F representing the most abundant toxin (47.5% of total venom proteome). Coagulation FV-activating serine proteinase (RVV-V, 14%), the PIV-SVMP activator of FX (RVV-FX, 8.5%), and less abundant toxins from nine protein families, make up its venom proteome. Venom composition-pathology correlations of D. siamensis envenomings in Taiwan are discussed. The lethal effect of Taiwanese D. siamensis venom was 0.47 mg/g mouse. Antivenomics-guided assessment of the toxin recognition landscape of the Taiwanese Russell’s viper antivenom, in conjunction with complementary in vivo neutralization analysis, informed the antivenom’s maximal toxin immunorecognition ability (14 mg total venom proteins/vial), neutralization capacity (6.5 mg venom/vial), and relative content of lethality neutralizing antibodies (46.5% of the toxin-binding F(ab’)₂ antibodies). The antivenomics analysis also revealed suboptimal aspects of the CDC-Taiwan antivenom. Strategies to improve them are suggested.

Venom proteomics and antivenom neutralization for the Chinese eastern Russell's viper, Daboia siamensis from Guangxi and Taiwan

The eastern Russell's viper (Daboia siamensis) causes primarily hemotoxic envenomation. Applying shotgun proteomic approach, the present study unveiled the protein complexity and geographical variation of eastern D. siamensis venoms originated from Guangxi and Taiwan. The snake venoms from the two geographical locales shared comparable expression of major proteins notwithstanding variability in their toxin proteoforms. More than 90% of total venom proteins belong to the toxin families of Kunitz-type serine protease inhibitor, phospholipase A2, C-type lectin/lectin-like protein, serine protease and metalloproteinase. Daboia siamensis Monovalent Antivenom produced in Taiwan (DsMAV-Taiwan) was immunoreactive toward the Guangxi D. siamensis venom, and effectively neutralized the venom lethality at a potency of 1.41 mg venom per ml antivenom. This was corroborated by the antivenom effective neutralization against the venom procoagulant (ED = 0.044 ± 0.002 µl, 2.03 ± 0.12 mg/ml) and hemorrhagic (ED50 = 0.871 ± 0.159 µl, 7.85 ± 3.70 mg/ml) effects. The hetero-specific Chinese pit viper antivenoms i.e. Deinagkistrodon acutus Monovalent Antivenom and Gloydius brevicaudus Monovalent Antivenom showed negligible immunoreactivity and poor neutralization against the Guangxi D. siamensis venom. The findings suggest the need for improving treatment of D. siamensis envenomation in the region through the production and the use of appropriate antivenom.

Synergistic strategies of predominant toxins in snake venoms

Synergism is a significant phenomenon present in snake venoms that may be an evolving strategy to potentiate toxicities. Synergism exists between different toxins or toxin complexes in various snake venoms, with phospholipaseA₂s (PLA₂s) (toxins or subunits) the main enablers. The predominant toxins, snake venom PLA₂s, metalloproteases (SVMPs), serine proteases (SVSPs) and three-finger toxins (3FTxs), play essential roles in synergistic processes. The hypothetical mechanisms of synergistic effect can be generalized under the effects of amplification and chaperoning. The Toxicity Score is among the few quantitative methods to assess synergism. Selection of toxins involved in synergistically enhanced toxicity as the targets are important for development of novel antivenoms or inhibitors.

Single Chain Antibody Fragment against Venom from the Snake Daboia russelii formosensis

Russell's vipers containing hemotoxic and neurotoxic venom commonly cause snake envenomation. Horse-derived antivenom is a specific antidote, but its production is expensive and has side effects. Developing a cost-effective and more tolerable therapeutic strategy is favorable. In this study, using glutaraldehyde-attenuated Daboia russelii formosensis (DRF) venom proteins to immunize chickens, polyclonal yolk-immunoglobulin (IgY) antibodies were generated and showed a specific binding affinity. Phage display technology was used to generate two antibody libraries of single-chain variable fragments (scFvs) containing 3.4 × 10⁷ and 5.5 × 10⁷ transformants, respectively. Phage-based ELISA indicated that specific clones were enriched after bio-panning. The nucleotide sequences of scFv-expressing clones were analyzed and classified into six groups in the short linker and four groups in the long linker. These scFv antibodies specifically bound to DRF proteins, but not other venom proteins. Mass spectrometric data suggested that these scFv antibodies may recognize phospholipase A2 RV-4 or RV-7. In vivo studies showed that anti-DRF IgY exhibited complete protective effects and mixed scFv antibodies increased the survival rate and time of mice challenged with a lethal dose of DRF proteins. These antibodies can be potentially applied in a rapid diagnostic method or for treatment in the future.

Unraveling the Proteome Composition and Immuno-profiling of Western India Russell's Viper Venom for In-Depth Understanding of Its Pharmacological Properties, Clinical Manifestations, and Effective Antivenom Treatment

The proteome composition of western India (WI) Russell's viper venom (RVV) was correlated with pharmacological properties and pathological manifestations of RV envenomation. Proteins in the 5-19 and 100-110 kDa mass ranges were the most predominate (∼35.1%) and least abundant (∼3.4%) components, respectively, of WI RVV. Non-reduced SDS-PAGE indicated the occurrence of multiple subunits, non-covalent oligomers, self-aggregation, and/or interactions among the RVV proteins. A total of 55 proteins belonging to 13 distinct snake venom families were unambiguously identified by ESI-LC-MS/MS analysis. Phospholipase A2 (32.5%) and Kunitz-type serine protease inhibitors (12.5%) represented the most abundant enzymatic and non-enzymatic proteins, respectively. However, ATPase, ADPase, and hyaluronidase, detected by enzyme assays, were not identified by proteomic analysis owing to limitations in protein database deposition. Several biochemical and pharmacological properties of WI RVV were also investigated. Neurological symptoms exhibited by some RV-bite patients in WI may be correlated to the presence of neurotoxic phospholipase A2 enzymes and Kunitz-type serine protease inhibitor complex in this venom. Monovalent antivenom was found to be better than polyvalent antivenom in immuno-recognition and neutralization of the tested pharmacological properties and enzyme activities of WI RVV; nevertheless, both antivenoms demonstrated poor cross-reactivity and neutralization of pharmacological activities shown by low-molecular-mass proteins (<18 kDa) of this venom.

Neurotoxicity in snakebite--the limits of our knowledge

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

Refolding by high pressure of a toxin containing seven disulfide bonds: bothropstoxin-1 from Bothrops jararacussu

Aggregation is a serious obstacle for recovery of biologically active heterologous proteins from inclusion bodies (IBs) produced by recombinant bacteria. E. coli transformed with a vector containing the cDNA for Bothropstoxin-1 (BthTx-1) expressed the recombinant product as IBs. In order to obtain the native toxin, insoluble and aggregated protein was refolded using high hydrostatic pressure (HHP). IBs were dissolved and refolded (2 kbar, 16 h), and the effects of protein concentration, as well as changes in ratio and concentration of oxido-shuffling reagents, guanidine hydrochloride (GdnHCl), and pH in the refolding buffer, were assayed. A 32% yield (7.6 mg per liter of bacterial culture) in refolding of the native BthTx-1 was obtained using optimal conditions of the refolding buffer (Tris-HCl buffer, pH 7.5, containing 3 mM of a 2:3 ratio of GSH/GSSG, and 1 M GdnHCl). Scanning electron microscopy (SEM) showed that that disaggregation of part of IBs particles occurred upon compression and that the morphology of the remaining IBs, spherical particles, was not substantially altered. Dose-dependent cytotoxic activity of high-pressure refolded BthTx-1 was shown in C2C12 muscle cells.

Enzymatic toxins from snake venom: structural characterization and mechanism of catalysis

Snake venoms are cocktails of enzymes and non-enzymatic proteins used for both the immobilization and digestion of prey. The most common snake venom enzymes include acetylcholinesterases, l-amino acid oxidases, serine proteinases, metalloproteinases and phospholipases A(2) . Higher catalytic efficiency, thermal stability and resistance to proteolysis make these enzymes attractive models for biochemists, enzymologists and structural biologists. Here, we review the structures of these enzymes and describe their structure-based mechanisms of catalysis and inhibition. Some of the enzymes exist as protein complexes in the venom. Thus we also discuss the functional role of non-enzymatic subunits and the pharmacological effects of such protein complexes. The structures of inhibitor-enzyme complexes provide ideal platforms for the design of potent inhibitors which are useful in the development of prototypes and lead compounds with potential therapeutic applications.

Protein complexes in snake venom

Snake venom contains mixture of bioactive proteins and polypeptides. Most of these proteins and polypeptides exist as monomers, but some of them form complexes in the venom. These complexes exhibit much higher levels of pharmacological activity compared to individual components and play an important role in pathophysiological effects during envenomation. They are formed through covalent and/or non-covalent interactions. The subunits of the complexes are either identical (homodimers) or dissimilar (heterodimers; in some cases subunits belong to different families of proteins). The formation of complexes, at times, eliminates the non-specific binding and enhances the binding to the target molecule. On several occasions, it also leads to recognition of new targets as protein-protein interaction in complexes exposes the critical amino acid residues buried in the monomers. Here, we describe the structure and function of various protein complexes of snake venoms and their role in snake venom toxicity.

Snake venomics of the Siamese Russell's viper (Daboia russelli siamensis) -- relation to pharmacological activities

The venom proteome of Daboia russelli siamensis, a snake of medical importance in several Asian countries, was analysed by 2-D electrophoresis, subsequent MS/MS and enzymatic assays. The proteome comprises toxins from six protein families: serine proteinases, metalloproteinases, phospholipases A(2), L-amino acid oxidases, vascular endothelial growth factors and C-type lectin-like proteins. The venom toxin composition correlates with the clinical manifestation of the Russell's viper bite and explains pathological effects of the venom such as coagulopathy, oedema, hypotensive, necrotic and tissue damaging effects. The vast majority of toxins are potentially involved in coagulopathy and neurotoxic effects. The predominant venom components are proteinases capable of activating blood coagulation factors and promoting a rapid clotting of the blood, and neurotoxic phospholipase A(2)s. The analysis of the venom protein composition provides a catalogue of secreted toxins. The proteome of D. r. siamensis exhibits a lower level of toxin diversity than the proteomes of other viperid snakes. In comparison to the venoms of Vipera ammodytes ammodytes and Vipera ammodytes meridionalis, the venom from D. r. siamensis showed quantitative differences in the proteolytic, phospholipase A(2), L-amino acid oxidase and alkaline phosphatase activities.

Phospholipase A2 genes and their expressions in Thai Russell's viper venom glands

Phospholipase A2 (PLA2) is a multi-functional enzyme found in many snake venoms and exists in several isoforms. PLA2 causes a variety of pathological effects including anticoagulant, edema, and platelet aggregation inhibition. Here, we reported the cDNA and gene sequences of PLA2 and their expressions in Thai Russell's viper (RV) Daboia russellii siamensis venom glands. We identified 3 PLA2 genes in the RV genome, 2 of which are actively transcribed in the venom gland. The deduced amino acids of these 2 PLA2 isoforms share 80% identity and are the same as PLA2s from Taiwan Russell's viper, Daboia russellii formosensis. A third PLA2 gene has no corresponding mRNA transcript from the venom gland suggesting a very low level of expression in the venom glands.

New insights into the functions and N-glycan structures of factor X activator from Russell's viper venom

The coagulation factor X activator from Russell's viper venom (RVV-X) is a heterotrimeric glycoprotein. In this study, its three subunits were cloned and sequenced from the venom gland cDNAs of Daboia siamensis. The deduced heavy chain sequence contained a C-terminal extension with four additional residues to that published previously. Both light chains showed 77-81% identity to those of a homologous factor X activator from Vipera lebetina venom. Far-western analyses revealed that RVV-X could strongly bind protein S, in addition to factors X and IX. This might inactivate protein S and potentiate the disseminated intravascular coagulation syndrome elicited by Russell's viper envenomation. The N-glycans released from each subunit were profiled and sequenced by MALDI-MS and MS/MS analyses of the permethyl derivatives. All the glycans, one on each light chain and four on the heavy chain, showed a heterogeneous pattern, with a combination of variable terminal fucosylation and sialylation on multiantennary complex-type sugars. Amongst the notable features were the presence of terminal Lewis and sialyl-Lewis epitopes, as confirmed by western blotting analyses. As these glyco-epitopes have specific receptors in the vascular system, they possibly contribute to the rapid homing of RVV-X to the vascular system, as supported by the observation that slower and fewer fibrinogen degradation products are released by desialylated RVV-X than by native RVV-X.

Phospholipase A2 diversity and polymorphism in European viper venoms: Paradoxical molecular evolution in Viperinae

We report the diversity and polymorphism of phospholipase A(2) (PLA(2)) transcripts from snakes belonging to nine European viper subspecies. This diversity results in the expression of a combination of six PLA(2) species--ammodytin I1, ammodytin I2, ammodytin L, ammodytoxin, vaspin A and vaspin B--with 19 known isoforms of the first five of these species. Most of the European viper venoms studied contained either a myotoxin or a neurotoxin, and all contained ammodytin I1 and ammodytin I2. There is no evidence that a given pattern of PLA(2) species constitutes a taxonomic criterion, and isoform analysis would be required for such discrimination. Analysis of the phylogenetic relationships between PLA(2) species from European vipers and those of other members of the Viperinae revealed a strong correlation between the geographical source of the viper and the clustering seen for the different isoforms, for each PLA(2) species. The K(a)/K(s) values calculated for the mature protein-coding region of paralogous genes showed that ratios for pairs including vaspin B or one ammodytoxin isoform were greater than 1.09, whereas those for most of the remaining pairs were less than 1. Different patterns of mutation were observed in comparisons of the different PLA(2) isoforms. The mechanisms directing a mutation toward a precise exon remain unresolved.

Venom phospholipases of Russell's vipers from Myanmar and eastern India--cloning, characterization and phylogeographic analysis

Venoms of Russell's vipers (genus Daboia) are known for their deadly coagulopathic and other effects. We herein studied various isoforms of venom phospholipases A(2) (PLAs) from two Daboia species at their geographic boundary. From Myanmar Daboia siamensis venom (designated as DsM), four PLAs (designated DsM-aI, aI', aII' and bI') were purified, and the cDNAs encoding two acidic (DsM-aI and aII) and two basic PLAs (DsM-bI and S1) were also cloned from its venom-glands. DsM-S1 is identical to the major venom PLA of southern India Daboia russelii, but the protein is absent from the venom. Additionally, four PLAs (designated DrK-aI, aII, bI and bII) were cloned from cDNA obtained from venom glands of a Kolkata D. russelii, and the PLAs were purified from the pooled venom (designated as DrK). The acidic DrK-aI is the most neurotoxic and lethal among these PLAs; DsM-aI which differs from DrK-aI by only the Phe2 substitution shows greatly reduced enzymatic activity and lethality. Both acidic PLAs do not form dimeric complex with basic PLAs in the same venoms. DsM-bI' is neurotoxic and lethal but its orthologous DrK-bI (97% identical to DsM-bI') is a much weaker toxin. Given the fact that most of the orthologous PLAs of DrK and DsM share 97-100% sequence identity, Daboia vipers of Myanmar and Kolkata must be closely related. Molecular phylogenetic analyses on 30 venom PLAs of Eurasian vipers' revealed co-evolution of five subtypes of venom PLAs in both Daboia and Vipera genera. Our results shed light on the intra- and inter-species variations and structure-function relationships of viperid venom PLAs.

Influence of phospholipases A2 from snake venoms on survival and neurite outgrowth in pheochromocytoma cell line PC12

To determine whether the ability to induce neurite outgrowth in rat pheochromocytoma cell line PC12 is characteristic of phospholipases of different types, we have studied the influence of phospholipase A(2) (PLA2) from cobra Naja kaouthia venom and two PLA2s from viper Vipera nikolskii venom on PC12 cells. Phospholipases from the viper venom are heterodimers in which only one of the subunits is enzymatically active, while PLA2 from the cobra venom is a monomer. It was found that all three PLA2s induce neurite outgrowth in PC12. The PLA2 from cobra venom exhibits this effect at higher concentrations as compared to the viper enzymes. We have not observed such an activity for isolated subunits of viper PLA2s, since the enzymatically active subunits have very high cytotoxicity, while the other subunits are not active at all. However, co-incubation of active and inactive subunits before addition to the cells leads to a marked decrease in cytotoxicity and to restoration of the neurite-inducing activity. It has also been shown that all enzymatically active PLA2s are cytotoxic, the PLA2 from cobra venom being the least active. Thus, for the first time we have shown that PLA2s from snake venoms can induce neurite outgrowth in PC12 cells.

Antivenom treatment and renal dysfunction in Russell's viper snakebite in Taiwan: a case series

Formosan Russell's viper (Daboia russelli siamensis) is the sixth most frequent cause of snakebites in Taiwan. Its bite induces greater kidney injury than other Russell's vipers in Southeast Asia. Poor availability of antivenom might be the major reason. To enhance treatment, we supplied the antivenom to the teaching hospitals that are near the areas where D. r. siamensis is found. We also used an ELISA in diagnosis. From June 1999 to December 2001, a total of 13 cases of D. r. siamensis snakebite were diagnosed with serum venom level of 10-98 ng/ml, 1-6 hours after being envenomed. Abnormal coagulation function and acute renal failure occurred early and were the two most important clinical features. Early specific antivenom treatment, 3-6 hours after systemic envenoming, restored the coagulation function in 1-2 days and seemed to be statistically effective in reducing the severity of renal damage compared with the historical and delayed group by the Wilcoxon rank-sum test. Two to four vials of antivenom were needed to block the systemic toxicity and produced few side effects. The antivenom should be administered as early as possible to prevent systemic dysfunction.

Time-course of lipid peroxidation in different organs of mice treated with Echis pyramidum snake venom

This study examined the effect of Echis pyramidum (EP) venom on time-course of lipid peroxidation in different vital organs of mice. Adult male Swiss albino mice were injected with EP venom (2 mg/kg, i.p.); control mice received vehicle alone (normal saline). Mice were killed at 1, 3, 6, 12, and 24 h post-envenomation. The liver, lung, kidney, heart, and brain (cerebrum and cerebellum) were collected for the estimation of malondialdehyde (MDA), an index of lipid peroxidation. The results of this study showed that a single injection of EP venom caused a significant lipid peroxidation in all the organs studied. The onset of lipid peroxidation was as early as 1 h and persisted for several hours, suggesting an important role of oxidative stress in the cytotoxicity of EP venom.

Basic amino acid residues in the β-structure region contribute, but not critically, to presynaptic neurotoxicity of ammodytoxin A

The molecular mechanism of action of presynaptically toxic secreted phospholipases A2 (sPLA2s) isolated from snake venoms is not completely understood. It has been proposed that the positive charge in the beta-structure region is important for their toxic activity. To test this hypothesis, we characterised several mutants of ammodytoxin A (AtxA) possessing substitution of all five basic residues in this region. The mutations had relatively little influence on the catalytic activity of AtxA, either on charge-neutral or anionic phospholipid vesicles. An exception was R72 when replaced by a hydrophobic (higher activity) or an acidic (lower activity) residue. Lethal potencies of the eight single site mutants were up to four times lower than that of the wild-type, whereas the triple mutant (K74S/H76S/R77L) was 13-fold less toxic. The substitutions also lowered the affinity of the toxin, slightly to moderately, for the neuronal receptors R25 and R180. Interaction with calmodulin was only slightly affected by substitutions of K86, more by those of the K74/H76/R77 cluster and most by those of R72 (up to 11-fold lower binding affinity). The results clearly indicate that the basic amino acid residues in the beta-region of AtxA contribute to, but are not necessary for, its neurotoxic effect.

The X-ray structure of a snake venom Gln48 phospholipase A2 at 1.9Å resolution reveals anion-binding sites

Phospholipase A2 is an "interfacial" enzyme and its binding to negatively charged surfaces is an important step during catalysis. The Gln48 phospholipase A2 from the venom of Vipera ammodytes meridionalis plays the role of chaperone and directs a toxic His48 PLA2 onto its acceptor. In the venom the two phospholipases A2 exist as a postsynaptic neurotoxic complex, Vipoxin. The X-ray structure of Gln48 PLA2, complexed to sulphate ions, which mimic the negatively charged groups of anionic membranes, has been determined by the molecular replacement method and refined to 1.9A resolution. The protein forms a homodimer stabilized by ionic, hydrophobic, and hydrogen-bond interactions. The structure reveals two anion-binding sites per subunit. These sites are probably involved in interactions with the negatively charged membrane surface and, in this way, in the "targeting" of the toxic component to the receptors of the postsynaptic membranes. In the absence of the chaperone subunit the toxin changes the target of the physiological attack. A comparison of the homodimeric Gln48 PLA2 structure with that of the heterodimeric Vipoxin reveals differences in regions involved in the pharmacological activity of the toxin. This fact, except the active site histidine substitution, can explain the absence of toxicity in the Gln48 protein in comparison to the His48 phospholipase A2.

Crystallization and preliminary X-ray diffraction studies of a toxic phospholipase A2 from the venom of Vipera ammodytes meridionalis complexed to a synthetic inhibitor

A toxic phospholipase A(2) (PLA(2)) is isolated from the neurotoxic complex Vipoxin, the major lethal component of the venom of Vipera ammodytes meridionalis. The enzyme is complexed to the synthetic inhibitor elaidoylamide and crystallized. The crystals belong to the space group P2(1)2(1)2(1), with unit cell dimensions a=46.57 A, b=82.68 A, c=119.47 A and beta=90 degrees. Initial diffraction data to 3.3 A resolution are collected.

Sequences and structural organization of phospholipase A2 genes from Vipera aspis aspis, V. aspis zinnikeri and Vipera berus berus venom. Identification of the origin of a new viper population based on ammodytin I1 heterogeneity

We used a PCR-based method to determine the genomic DNA sequences encoding phospholipases A2 (PLA2s) from the venoms of Vipera aspis aspis (V. a. aspis), Vipera aspis zinnikeri (V. a. zinnikeri), Vipera berus berus (V. b. berus) and a neurotoxic V. a. aspis snake (neurotoxic V. a. aspis) from a population responsible for unusual neurotoxic envenomations in south-east France. We sequenced five groups of genes, each corresponding to a different PLA2. The genes encoding the A and B chains of vaspin from the neurotoxic V. a. aspis, PLA2-I from V. a. zinnikeri, and the anticoagulant PLA2 from V. b. berus are described here. Single nucleotide differences leading to amino-acid substitutions were observed both between genes encoding the same PLA2 and between genes encoding different PLA2s. These differences were clustered in exons 3 and 5, potentially altering the biological activities of PLA2. The distribution and characteristics of the PLA2 genes differed according to the species or subspecies. We characterized for the first time genes encoding neurotoxins from the V. a. aspis and V. b. berus snakes of central France. Genes encoding ammodytins I1 and I2, described previously in Vipera ammodytes ammodytes (V. am. ammodytes), were also present in V. a. aspis and V. b. berus. Three different ammodytin I1 gene sequences were characterized: one from V. b. berus, the second from V. a. aspis, V. a. zinnikeri and the neurotoxic V. a. aspis, and the third from the neurotoxic V. a. aspis. This third sequence was identical with the reported sequence of the V. am. ammodytes ammodytin I1 gene. Genes encoding monomeric neurotoxins of V. am. ammodytes venom, ammodytoxins A, B and C, and the Bov-B LINE retroposon, a phylogenetic marker found in V. am. ammodytes genome, were identified in the genome of the neurotoxic V. a. aspis. These results suggest that the population of neurotoxic V. a. aspis snakes from south-east France may have resulted from interbreeding between V. a. aspis and V. am. ammodytes.

Toxicity evolution of Vipera aspis aspis venom: identification and molecular modeling of a novel phospholipase A(2) heterodimer neurotoxin

We report the simultaneous presence of two phospholipase A(2) (PLA(2)) neurotoxins in the venom of Vipera aspis aspis, the first such observation. One is monomeric and identical to ammodytoxin B of Vipera ammodytes ammodytes. Its presence may result from gene flux after interbreeding between V. aspis aspis and V. ammodytes ammodytes. The second, a novel heterodimer named vaspin, is very similar to vipoxin of Vipera ammodytes meridionalis and to PLA(2)-I of Vipera aspis zinnikeri. It may result from expression of preexisting genes, the acidic subunit evolving from an ancestor common to ammodytin I2 from V. ammodytes ammodytes, which we also found in V. aspis aspis.

Russell's viper snakebite in Taiwan: differences from other Asian countries

Formosan Russell's viper (Daboia russelli siamensis) is the sixth most frequent cause of snakebite in Taiwan. Its venom has been thought to have both neurotoxic and hematoxic properties. This viper's snakebite is rare and thus scarcely subjected to systemic studies. In this paper, we retrospectively analyzed and described 18 cases of viper snakebite from 1987 to 1999. Like that of the Russell's viper snakebite in other South East Asian areas, varied degrees of acute renal failure, incoagulable blood with bleeding diathesis and hemolysis were the major symptoms found in the systemic envenoming patients. Systemic thrombosis seems to be the distinguishing feature in Formosan Russell's viper snakebite. Neither symptoms nor signs of neuromuscular junction blocking effects were observed, which is another difference from symptoms observed after bites of some other Russell's viper subspecies, suggesting a significant geographic variation. These findings confirmed the clinical importance of Russell's viper snakebite in Taiwan.

Purification and characterization of a potent hemolytic toxin with phospholipase A2 activity from the venom of Indian Russell's viper

A potent toxin with phospholipase A2 (PLA2) and hemolytic activity in vitro was purified from the Russell's viper venom of eastern India (RVV-EI). The purified protein (RVV-PFIIc') of 15.3 kDa molecular weight, and a lethal toxicity dose (LD50i.p.) of 0.1 mg/kg body weight, was the most toxic PLA2 so far reported from the Indian subcontinent. The material also possessed anticoagulant activity as it enhanced the prothrombin induced plasma clotting time in vitro. The PLA2 toxin (RVV-PFIIc') was shown to be different from other PLA2s of RVV in respect to one or more of these parameters e.g. molecular weight, isoelectric pH, in vivo toxicity, specific activity of the enzyme and certain other biological activities. The first 19 amino terminal sequence (NLFQFAEMIVKMTGKEAVH) of RVV-PFIIc' showed variable degree of homology (42.1-94.7%) with those of other RVV-PLA2s described in the literature. Antisera raised against RVV-EI or RVV-PFIIc', though completely neutralized the in vivo lethal toxicity of RVV-EI or RVV-PFIIc', failed to inhibit their PLA2 activity in vitro thereby suggesting that in vivo toxicity and in vitro activity of the enzyme may not be directly related. Apart from RVV-PFIIc', at least two other PLA2 isozymes were found to be present in RVV-EI that were distinct from RVV-PFIIc' in respect to their molecular, biological as well as serological properties. The significance of these and related data in antivenom therapy is discussed.

Phenylalanine-24 in the N-terminal region of ammodytoxins is important for both enzymic activity and presynaptic toxicity

Ammodytoxins (Atxs) are group II phospholipases A(2) (PLA(2)s) with presynaptic toxicity from venom of the snake Vipera ammodytes ammodytes. The molecular basis of their neurotoxicity, and that of similar PLA(2) toxins, is still to be explained. To address this problem, a surface-exposed aromatic residue, Phe(24), in the N-terminal region of the most potent Atx, AtxA, was replaced by other aromatic (tyrosine, tryptophan), hydrophobic (alanine) and polar uncharged (serine, asparagine) residues. The mutants were produced in the bacterial expression system, refolded in vitro and purified to homogeneity. All but the Trp(24) mutant, whose activity was similar to that of the wild type, showed a considerable decrease (40-80%) in enzymic activity on a micellar phosphatidylcholine substrate. This result indicates an important role for the aromatic side chains of phenylalanine or tryptophan, but not tyrosine, in PLA(2) activity, very likely at a stage of interfacial adsorption of the enzyme to zwitterionic aggregated substrates. The substitutions of Phe(24) also significantly decreased toxicity in mice, with the most prominent decrease, of 130-fold, observed in the case of the Asn(24) mutant. The results with the mutants show that there is no correlation between enzymic activity, lethality and binding affinity for three AtxA neuronal receptors (R180, R25 and calmodulin). Our results suggest a critical involvement of Phe(24) in the neurotoxicity of AtxA, apparently at a stage which does not involve the interaction with the known Atx-binding neuronal proteins and catalytic activity.

Structure and phylogeny of the venom group I phospholipase A(2) gene

Phospholipases A(2) (PLA(2)s) catalyzing the hydrolysis of phospholipids form a family of proteins with diverse physiological and pharmacological properties. While there have been several reports on the cloning of PLA(2) cDNAs, very few studies have been carried out on the PLA(2) genes and, most importantly, no information has been available on the gene structure and function of group I venom PLA(2). This study, on the PLA(2) gene from a spitting cobra, besides being the very first report on any venom group I PLA(2) gene, constitutes the missing link in the biology and evolution of phospholipases. The 4-kb gene consists of four exons and three introns and resembles the human pancreatic PLA(2) gene. However, the size of intron 3 in particular is much smaller than that in the pancreatic gene. Interestingly, the information for the toxic and most of the pharmacological properties of the venom PLA(2) can be attributed to the end of exon 3 and the whole of exon 4 of the gene. This functional delineation fits in well with the theory of adaptive evolution exhibited by the venom PLA(2)s. We also show that the mammalian pancreatic and elapid PLA(2)s have similar paths of evolution (probably following gene duplication) from a common ancestral gene. Venom group II phospholipases, although evolved from the same ancestor, diverged early in evolution from the group I PLA(2) genes. Intriguingly, CAT reporter gene assays and DNase 1 footprinting studies on the promoter and its deletion constructs using CHO and HepG2 cell lines identified the possible involvement of cis elements such as Sp1, AP2, gamma-IRE, and (TG)(12) repeats in the expression of the gene in a tissue-specific manner.

Phospholipase A(2) with platelet aggregation inhibitor activity from Austrelaps superbus venom: protein purification and cDNA cloning

Four phospholipase A(2) (PLA(2)) enzymes (Superbins a, b, c, and d) with varying platelet aggregation inhibitor activities have been purified from Austrelaps superbus by a combination of gel filtration, ion-exchange, and reversed-phase high-pressure liquid chromatography. Purity and homogeneity of the superbins have been confirmed by high-performance capillary zone electrophoresis and mass spectrometry. The electron spray ionization mass spectrometry data showed that their molecular masses range from 13,140 to 13,236 Da. Each of the proteins has been found to be basic and exhibit varying degrees of PLA(2) activity. They also displayed different platelet aggregation inhibitory activities. Superbin a was found to possess the most potent inhibitory activity with an IC(50) of 9.0 nM, whereas Superbin d was found to be least effective with an IC(50) of 3.0 microM. Superbins b and c were moderately effective with IC(50) values of 0.05 and 0.5 microM, respectively. The amino-terminal sequencing confirmed the identity of these superbins. cDNA cloning resulted in the identification of 17 more PLA(2) isoforms in A. superbus venom. It has also provided complete information on the precursor PLA(2). The precursor PLA(2) contained a 27-amino-acid signal peptide and 117- to 125-amino-acid PLA(2) (molecular mass ranging from 13,000 to 14,000 Da). Two of these PLA(2) enzymes resembled more closely (87%) Superbin a in structure. Two unique PLA(2) enzymes containing an extra pancreatic loop also have been identified among the isoforms.

Molecular evolution of snake toxins: is the functional diversity of snake toxins associated with a mechanism of accelerated evolution?

Recent studies revealed that animal toxins with unrelated biological functions often possess a similar architecture. To tentatively understand the evolutionary mechanisms that may govern this principle of functional prodigality associated with a structural economy, two complementary approaches were considered. One of them consisted of investigating the rates of mutations that occur in cDNAs and/or genes that encode a variety of toxins with the same fold. This approach was largely adopted with phospholipases A2 from Viperidae and to a lesser extent with three-fingered toxins from Elapidae and Hydrophiidae. Another approach consisted of investigating how a given fold can accommodate distinct functional topographies. Thus, a number of topologies by which three-fingered toxins exert distinct functions were investigated either by making chemical modifications and/or mutational analyses or by studying the three-dimensional structure of toxin-target complexes. This review shows that, although the two approaches are different, they commonly indicate that most if not all the surface of a snake toxin fold undergoes natural engineering, which may be associated with an accelerated rate of evolution. The biochemical process by which this phenomenon occurs remains unknown.

X-ray structure at 1.76 A resolution of a polypeptide phospholipase A2 inhibitor

The high resolution crystal structure of a natural PLA2 inhibitor has been determined by Patterson search methods. In the heterodimeric, neurotoxic complex, vipoxin, isolated from the venom of Bulgarian viper, PLA2 inhibitor represents the non-toxic subunit. The model was refined to a crystallographic R-factor of 15.5% for data between 6 and 1.76 A resolution. The packing of the inhibitor in the crystal reveals close contacts between the molecules, which are symmetry-related by the 2-fold axes of the lattice. These pairs associate as a crystallographic dimer, stabilized by a set of interactions, including van der Waals contacts between residues from symmetry-related pairs, denoted as the recognition site and the recognition surface. Residues Ph3, Trp31 and Tyr119 represent the recognition site of inhibitor which possibly fits to the hydrophobic wall of the target PLA2. The topology of the inhibitor represents the PLA2 type of folding: three long helices and a beta-hairpin. Superposition of the structure of the inhibitor shows an almost complete overlap with different mammalian and viper PLA2 in the backbone and in the position of the sidechains of the residues that belong to the active centre and the hydrophobic wall. A "lock and key" mechanism of recognition of its native PLA2 in gland cells and other toxic PLA2 in vitro has been suggested. The mechanism includes complementary "head to tail" interactions between the recognition site of the inhibitor and a recognition surface located on the hydrophobic wall of the target PLA2. Having a high spatial homology with the PLA2 family of enzymes but opposing their action, the inhibitor from vipoxin presents an example of a divergent evolution of an ancient PLA2. The presence of a space for binding calcium in the inhibitor is believed to be a rudiment and proof of a common origin with PLA2.

Molecular cloning and deduced primary structures of acidic and basic phospholipases A2 from the venom of Deinagkistrodon acutus

This paper presents the nucleotide sequences of the cDNAs encoding three acidic phospholipases A2 and one basic phospholipase A2 from Deinagkistrodon acutus venom. The deduced primary structure of the basic enzyme is closest to that of the basic neurotoxic enzyme from Trimeresurus mucrosquamatus venom, while the acidic phospholipases from D. acutus have highest sequence similarity to that from Agkistrodon halys pallas. The phylogeny of this monotypic species is discussed.

LYS-49 phospholipase A2 homologs from venoms of Deinagkistrodon acutus and Trimeresurus mucrosquamatus have identical protein sequence

The complete amino acid sequences of the Lys-49 PLA2s from the venom of Deinagkistrodon acutus (from Taiwan and China) and Trimeresurus mucrosquamatus (Taiwan habu) were solved by a facile cDNA cloning and sequencing method. The deduced amino acid sequences of the Lys-49 PLA2s of both venoms are identical, suggesting close phylogenic relationship between this two snake species of different genera. In addition, by cloning and cDNA sequencing, the mRNA coding for a Arg-49 PLA2 homolog of low expression level was also found in the venom gland of T. mucrosquamatus.

Synaptosomal binding of 125I-labelled daboiatoxin, a new PLA2 neurotoxin from the venom of Daboia russelli siamensis

Daboiatoxin (DbTx), the PLA2 neurotoxin from Daboia russelli siamensis venom, was shown to bind specifically and saturably to rat cerebrocortical synaptosomes and synaptic membrane fragments. Two families of binding sites were detected by equilibrium binding analysis in the presence and absence of Ca2+. Scatchard analysis of biphasic plateaus revealed Kdl 5 nM and Bmax1, 6 pmoles/mg protein, and Kd2 80 nM and Bmax2 20 pmoles/mg protein, respectively, for the high- and low-affinity binding sites. The binding of 125I-DbTx to synaptosomes did not show marked dependence on Ca2+, Mg2+, Co2+ and Sr2+. Native DbTx was the only strong competitor to 125I-DbTx synaptosomal binding (IC50 12.5 nM, KI 5.5 nM). Two other crotalid PLA2 neurotoxins, crotoxin CB and mojave toxin basic subunit, and nontoxic C. Atrox PLA2 enzyme, were relatively weaker inhibitors, while two viperid PLA2 neurotoxins, ammodytoxin A and VRV PL V, were very weak inhibitors. Crotoxin CA was a poor inhibitor even at microM concentrations, whereas no inhibitory effect at all was observed with crotoxin CACB, ammodytoxin C, VRV PL VIIIa, taipoxin, beta-bungarotoxin, or with PLA2 enzymes from N. naja venom, E. schistosa venom, bee venom and porcine pancreas. All other pharmacologically active ligands examined (epinephrine, norepinephrine, histamine, choline, dopamine, serotonin, GABA, naloxone, WB-4101, atropine, hexamethonium and alpha-bun-garotoxin) also failed to interfere with 125I-DbTx binding. As those competitors that showed partial inhibition were effective only at microM concentration range compared to the Kd (5 nM) of 125I-DbTx synaptosomal binding, DbTx could well recognize a different neuronal binding site. Rabbit anti-DbTx polyclonal antisera completely blocked the specific binding. When a range of Ca2+ and K+ channels modulators were examined, Ca2+ channel blockers (omega-conotoxins GVIA and MVIIC, taicatoxin, calciseptine and nitrendiprene) did not affect the binding even at high concentrations, while charybdotoxin was the only K+ channel effector that could partially displace 125I-DbTx synaptosomal binding amongst the K+ channel blockers tested (apamin, dendrotoxin-I, iberiotoxin, MCD-peptide, 4-aminopyridine and tetraethylammonium), suggesting that neither K+ nor Ca2+ channels are associated with DbTx binding sites.

Two types of Russell's viper revealed by variation in phospholipases A2 from venom of the subspecies

This study compared the phospholipases A2 (PLA2S) present in four commercially available venoms of Russell's viper subspecies by HPLC fractionation and partial sequence analysis. A potent heterodimeric PLA2 neurotoxin (designated a Russtoxin) was found in the venoms of all Russell's vipers except Daboia russelli (Sri Lanka and South India). The venom PLA2S of D. r. russelli (southern India) used in a previous study appear to be the same as those of D. r. pulchella (Sri Lanka), while the venom PLA2S of D. r. russelli (Pakistan) and D. r. siamensis (Burma and Thailand) resemble those of D. r. formosensis (Taiwan). This study provides evidence for the presence of two types of Russell's viper. Daboia russelli formosensis (Taiwan). D. r. siamensis (Thailand and Burma) and D. r. russelli (Pakistan) represent one type whose venom contains PLA2S having an Asn residue at the N-terminus, while D. r. pulchella (South India and Sri Lanka) represents the other type, whose venom contains PLA2S with a N-terminal residue Ser.