Biochemical characterization of the venom of the coral snake Micrurus tener and comparative biological activities in the mouse and a reptile model

Red-on-Yellow Queen: Bio-Layer Interferometry Reveals Functional Diversity Within Micrurus Venoms and Toxin Resistance in Prey Species

Snakes in the family Elapidae largely produce venoms rich in three-finger toxins (3FTx) that bind to the α 1 subunit of nicotinic acetylcholine receptors (nAChRs), impeding ion channel activity. These neurotoxins immobilize the prey by disrupting muscle contraction. Coral snakes of the genus Micrurus are specialist predators who produce many 3FTx, making them an interesting system for examining the coevolution of these toxins and their targets in prey animals. We used a bio-layer interferometry technique to measure the binding interaction between 15 Micrurus venoms and 12 taxon-specific mimotopes designed to resemble the orthosteric binding region of the muscular nAChR subunit. We found that Micrurus venoms vary greatly in their potency on this assay and that this variation follows phylogenetic patterns rather than previously reported patterns of venom composition. The long-tailed Micrurus tend to have greater binding to nAChR orthosteric sites than their short-tailed relatives and we conclude this is the likely ancestral state. The repeated loss of this activity may be due to the evolution of 3FTx that bind to other regions of the nAChR. We also observed variations in the potency of the venoms depending on the taxon of the target mimotope. Rather than a pattern of prey-specificity, we found that mimotopes modeled after snake nAChRs are less susceptible to Micrurus venoms and that this resistance is partly due to a characteristic tryptophan → serine mutation within the orthosteric site in all snake mimotopes. This resistance may be part of a Red Queen arms race between coral snakes and their prey.

In vivo neutralization of coral snake venoms with an oligoclonal nanobody mixture in a murine challenge model

Oligoclonal mixtures of broadly-neutralizing antibodies can neutralize complex compositions of similar and dissimilar antigens, making them versatile tools for the treatment of e.g., infectious diseases and animal envenomations. However, these biotherapeutics are complicated to develop due to their complex nature. In this work, we describe the application of various strategies for the discovery of cross-neutralizing nanobodies against key toxins in coral snake venoms using phage display technology. We prepare two oligoclonal mixtures of nanobodies and demonstrate their ability to neutralize the lethality induced by two North American coral snake venoms in mice, while individual nanobodies fail to do so. We thus show that an oligoclonal mixture of nanobodies can neutralize the lethality of venoms where the clinical syndrome is caused by more than one toxin family in a murine challenge model. The approaches described may find utility for the development of advanced biotherapeutics against snakebite envenomation and other pathologies where multi-epitope targeting is beneficial.

Quantifying venom production: A study on Micrurus snakes in Mexico

Our study quantifies venom production in nine Mexican coral snake species (Micrurus), encompassing 76 specimens and 253 extractions. Noteworthy variations were observed, with M. diastema and M. laticollaris displaying diverse yields, ranging from 0.3 mg to 59 mg. For animals for which we have length data, there is a relationship between size and venom quantity. Twenty-eight percent of the observed variability in venom production can be explained by snake size, suggesting that other factors influence the amount of obtained venom. These findings are pivotal for predicting venom effects and guiding antivenom interventions. Our data offer insights into Micrurus venom yields, laying the groundwork for future research and aiding in medical response strategies. This study advances understanding coral snake venom production, facilitating informed medical responses to coral snake bites.

Unveiling the Venom Composition of the Colombian Coral Snakes Micrurus helleri, M. medemi, and M. sangilensis

Little is known of the biochemical composition and functional features of the venoms of poorly known Colombian coral snakes. Here, we provide a preliminary characterization of the venom of two Colombian endemic coral snake species, Micrurus medemi and M. sangilensis, as well as Colombian populations of M. helleri. Electrophoresis and RP-HPLC techniques were used to identify venom components, and assays were conducted to detect enzyme activities, including phospholipase A2, hyaluronidase, and protease activities. The median lethal dose was determined using murine models. Cytotoxic activities in primary cultures from hippocampal neurons and cancer cell lines were evaluated. The venom profiles revealed similarities in electrophoretic separation among proteins under 20 kDa. The differences in chromatographic profiles were significant, mainly between the fractions containing medium-/large-sized and hydrophobic proteins; this was corroborated by a proteomic analysis which showed the expected composition of neurotoxins from the PLA2 (~38%) and 3FTx (~17%) families; however, a considerable quantity of metalloproteinases (~12%) was detected. PLA2 activity and protease activity were higher in M. helleri venom according to qualitative and quantitative assays. M. medemi venom had the highest lethality. All venoms decreased cell viability when tested on tumoral cell cultures, and M. helleri venom had the highest activity in neuronal primary culture. These preliminary studies shed light on the venoms of understudied coral snakes and broaden the range of sources that could be used for subsequent investigations of components with applications to specific diseases. Our findings also have implications for the clinical manifestations of snake envenoming and improvements in its medical management.

Antibodies against a single fraction of Micrurus dumerilii venom neutralize the lethal effect of whole venom

The coralsnake Micrurus dumerilii (Elapidae) is reported to cause envenomings of medical importance. Previous studies characterized the protein composition of its venom, with phospholipase A₂ (PLA₂) proteins the most abundant. However, it is unknown which venom components are responsible for its lethal toxicity. Fractionation of M. dumerilii venom from Colombia was carried out using RP-HPLC and each fraction was screened for lethal effect in mice at a dose of 20 μg by intraperitoneal route. Results showed that only one fraction, F9, was lethal. This fraction displayed PLA₂ activity, induced indirect hemolysis in vitro, as well as edema and myotoxicity in vivo. SDS-PAGE of unreduced F9 evidenced two bands of 8 and 15 kDa, respectively, consistent with the detection of proteins with masses of 13,217.77 Da, 7144.06 Da, and 7665.55 Da. Tryptic digestion of F9 followed by nESI-MS/MS revealed peptide sequences matching proteins of the three-finger toxin (3FTx) and PLA₂ families. Immunization of a rabbit with F9 proteins elicited antibody titers up to 1:10,000 by ELISA. After serum fractionation with caprylic acid, the obtained IgG was able to neutralize the lethal effect of the complete venom of M. dumerilii using a challenge of 2 ×LD₅₀ at the IgG/venom ratio of 50:1 (w/w). In conclusion, present results show that the lethal effect of M. dumerilii venom in mice is mainly driven by one fraction which contains 3FTx and PLA₂ proteins. The antibodies produced against this fraction cross-recognized other PLA₂s and neutralized the lethal effect of whole M. dumerilii venom, pointing out to the potential usefulness of F9 as a relevant antigen for improving current coral snake antivenoms.

Pharmacological Screening of Venoms from Five Brazilian Micrurus Species on Different Ion Channels

Coral snake venoms from the Micrurus genus are a natural library of components with multiple targets, yet are poorly explored. In Brazil, 34 Micrurus species are currently described, and just a few have been investigated for their venom activities. Micrurus venoms are composed mainly of phospholipases A₂ and three-finger toxins, which are responsible for neuromuscular blockade—the main envenomation outcome in humans. Beyond these two major toxin families, minor components are also important for the global venom activity, including Kunitz-peptides, serine proteases, 5′ nucleotidases, among others. In the present study, we used the two-microelectrode voltage clamp technique to explore the crude venom activities of five different Micrurus species from the south and southeast of Brazil: M. altirostris, M. corallinus, M. frontalis, M. carvalhoi and M. decoratus. All five venoms induced full inhibition of the muscle-type α1β1δε nAChR with different levels of reversibility. We found M. altirostris and M. frontalis venoms acting as partial inhibitors of the neuronal-type α7 nAChR with an interesting subsequent potentiation after one washout. We discovered that M. altirostris and M. corallinus venoms modulate the α1β2 GABA_AR. Interestingly, the screening on K_V1.3 showed that all five Micrurus venoms act as inhibitors, being totally reversible after the washout. Since this activity seems to be conserved among different species, we hypothesized that the Micrurus venoms may rely on potassium channel inhibitory activity as an important feature of their envenomation strategy. Finally, tests on Na_V1.2 and Na_V1.4 showed that these channels do not seem to be targeted by Micrurus venoms. In summary, the venoms tested are multifunctional, each of them acting on at least two different types of targets.

In vivo treatment with varespladib, a phospholipase A2 inhibitor, prevents the peripheral neurotoxicity and systemic disorders induced by Micrurus corallinus (coral snake) venom in rats

In this study, we investigated the action of varespladib (VPL) alone or in combination with a coral snake antivenom (CAV) on the local and systemic effects induced by Micrurus corallinus venom in rats. Adult male Wistar rats were exposed to venom (1.5 mg/kg - i.m.) and immediately treated with CAV (antivenom:venom ratio 1:1.5 'v/w' - i.p.), VPL (0.5 mg/kg - i.p.), or both of these treatments. The animals were monitored for 120 min and then anesthetized to collect blood samples used for haematological and serum biochemical analysis; after euthanasia, skeletal muscle, renal and hepatic tissue samples were collected for histopathological analysis. M. corallinus venom caused local oedema without subcutaneous haemorrhage or apparent necrosis formation, although there was accentuated muscle morphological damage; none of the treatments prevented oedema formation but the combination of CAV and VPL reduced venom-induced myonecrosis. Venom caused neuromuscular paralysis and respiratory impairment in approximately 60 min following envenomation; CAV alone did not prevent the neurotoxic action, whereas VPL alone prevented neurotoxic symptoms developing as did the combination of CAV and VPL. Venom induced significant increase of serum CK and AST release, mostly due to local and systemic myotoxicity, which was partially prevented by the combination of CAV and VPL. The release of hepatotoxic serum biomarkers (LDH and ALP) induced by M. corallinus venom was not prevented by CAV and VPL when individually administered; their combination effectively prevented ALP release. The venom-induced nephrotoxicity (increase in serum creatinine concentration) was prevented by all the treatments. VPL alone or in combination with CAV significantly prevented the venom-induced lymphocytosis. In conclusion, VPL shows to be effective at preventing the neurotoxic, nephrotoxic, and inflammatory activities of M. corallinus venom. In addition, VPL acts synergistically with antivenom to prevent a number of systemic effects caused by M. corallinus venom.

Transient Megaesophagus Following Coral Snake Envenomation in Three Dogs (2013-2018)

A 12 yr old dachshund, a 7 yr old English springer spaniel, and a 1.5 yr old French bulldog presented following envenomation by a coral snake. Each patient displayed evidence of varying degrees of lower motor neuron dysfunction, but all three developed transient megaesophagus. Two patients developed secondary aspiration pneumonia, with one requiring mechanical ventilation, which the owners declined, resulting in euthanasia. The third developed hypoventilation without aspiration pneumonia, was mechanically ventilated, and was successfully weaned. In the two surviving patients, the megaesophagus resolved by time of discharge. Coral snake envenomation is an uncommon occurrence, and these are the first documented cases of transient megaesophagus secondary to a North American species.

Protein composition and biochemical characterization of venom from Sonoran Coral Snakes (Micruroides euryxanthus)

The elapid genus, Micruroides, is considered the sister clade of all New World coral snakes (Genus Micrurus), is monotypic, and is represented by Sonoran Coral Snakes, Micruroides euryxanthus. Coral snakes of the genus Micrurus have been reported to have venoms that are predominantly composed of phospholipases A₂ (PLA₂) or three finger toxins (3FTx), but the venoms of the genus Micruroides are almost completely unstudied. Here, we present the first description of the venom of M. euryxanthus including identification of some proteins as well as transcriptomic, and biological activity assays. The most abundant components within M. euryxanthus venom are 3FTxs (62.3%) and there was relatively low proportion of PLA₂s (14.2%). The venom phenotype supports the hypothesis that the common ancestor of Micrurus and Micruroides had a 3FTx-dominated venom. Within the venom, there were two nearly identical α-neurotoxins (α-Ntx), one of which was designated Eurytoxin, that account for approximately 60% of the venom's lethality to mice. Eurytoxin was cloned, expressed in a soluble and active form, and used to produce rabbit hyperimmune serum. This allowed the analysis of its immunochemical properties, showing them to be different from the recombinant αNTx D.H., present in the venoms of some species of Micrurus. Finally, we observed that the commercial antivenom produced in Mexico for coral snake envenomation is unable to neutralize the lethality from M. euryxanthus venom. This work allowed the classification of Micruroides venom into the 3FTx-predominant group and identified the main components responsible for toxicity to mice.

Assessment of neutralization of Micrurus venoms with a blend of anti-Micrurus tener and anti-ScNtx antibodies

BACKGROUND

Micrurus venoms contain two main groups of toxic protein components: short-chain α-neurotoxins (SNtx) and phospholipases type A₂ (PLA₂). In North America, generally, the Micrurus venoms have low abundance of SNtx compared to that of PLA₂s; however, both are highly toxic to mammals, and consequently both can play a major role in the envenomation processes. Concerning the commercial horse-derived antivenoms against Micrurus from the North America region, they contain a relatively large amount of antibodies against PLA₂s, and a low content of antibodies against short chain α-neurotoxins. This is mainly due to the lower relative abundance of SNtxs, and also to its poor immunogenicity due to their size and nature. Hence, Micrurus antivenoms made in North America usually present low neutralizing capacity towards Micrurus venoms whose lethality depend largely on short chain α-neurotoxins, such as South American Micrurus species.

METHODS

Horses were hyperimmunized with either the venom of M. tener (PLA₂-predominant) or a recombinant short-chain consensus α-neurotoxin (ScNtx). Then, the combination of the two monospecific horse antibodies (anti-M. tener and anti-ScNtx) was used to test their efficacy against eleven Micrurus venoms.

RESULTS

The blend of anti-M. tener and anti-ScNtx antibodies had a better capacity to neutralize the lethality of diverse species from North, Central and South American Micrurus venoms. The antibodies combination neutralized both the ScNtx and ten out of eleven Micrurus venom tested, and particularly, it neutralized the venoms of M. distans and M. laticollaris that were neither neutralized by monospecific anti-M. tener nor anti-ScNtx.

CONCLUSIONS

These results provide a proof-of-principle for using recombinant immunogens to enrich poor or even non-neutralizing antisera against elapid venoms containing short chain α-neurotoxins to develop antivenoms with higher effectiveness and broader neutralizing capacity.

Myalgia as a Symptom of Envenomation by the Eastern Coral Snake, Micrurus Fulvius: A Case Report

We present the case of a patient who developed myalgia as the primary symptom of envenomation by the eastern coral snake, Micrurus fulvius. The patient was evaluated and treated in the emergency department. Physical examination did not demonstrate any neuromuscular abnormalities. On consultation with the poison control center, the patient's myalgia was determined to be an effect of envenomation, and 5 vials of North American coral snake antivenin were administered. The patient was admitted to the intensive care unit where his symptoms resolved. He was discharged the following day after remaining asymptomatic for 24 h.

Venoms of New World Vinesnakes (Oxybelis aeneus and O. fulgidus)

Species of Oxybelis are extremely elongate arboreal snakes that are broadly distributed in the Americas, from extreme southeastern Arizona (USA) to central South America. Primarily feeding on lizards and birds, Oxybelis venoms are poorly known in general, but a prominent taxon-specific three-finger toxin (fulgimotoxin) was isolated from and is a prominent component of O. fulgidus venom; a homolog is also present in O. aeneus venom. As part of ongoing characterization of venoms from rear-fanged snakes, we describe here the composition of two broadly distributed species, O. aeneus and O. fulgidus. Venom proteomes were of very low complexity, and four protein families (LAAO, PIII SVMP, CRiSP and 3FTx) account for more than 90% of total protein composition. Venoms from both species are moderately toxic to mice and to Hemidactylus geckos, but they are nearly an order of magnitude more toxic to Anolis lizards (a native prey species). These results reflect a trend in colubrid venom composition that is becoming increasingly more common: the presence of taxon-specific toxins, specifically three-finger toxins, preferentially targeting lizards and/or birds.

Actividad neurotóxica del veneno de serpientes del género Micrurus y métodos para su análisis. Revisión de la literatura

Introducción. Las serpientes del género Micrurus son animales de hábitos fosoriales, de temperamento pasivo y escasa producción de un potente veneno con características neurotóxicas que bloquean la transmisión sináptica en la placa neuromuscular.Objetivo. Presentar un panorama general de la neurotoxicidad del veneno de las serpientes Micrurus y su caracterización funcional mediante métodos de análisis ex vivo.Materiales y métodos. Se realizó una revisión de la literatura en MedLine y ScienceDirect usando términos específicos y sus combinaciones. Estrategia de búsqueda: tipo de estudios: artículos sobre la neurotoxicidad del veneno de serpientes Micrurus y técnicas para determinar su actividad neurotóxica mediante modelos in vitro, in vivo y ex vivo; periodo de publicación: sin limite inicial a junio de 2018; idiomas: inglés y español.Resultados. De los 88 estudios identificados en la búsqueda inicial, se excluyeron 28 por no cumplir los criterios de inclusión (basándose en la lectura de títulos y resúmenes); además, se incluyeron 8 documentos adicionales (libros e informes), que, a criterio de los autores, complementaban la información reportada por las referencias seleccionadas. Los estudios incluidos en la revisión (n=68) correspondieron a las siguientes tipologías: investigaciones originales (n=44), artículos de revisión (n=16) y capítulos de libros, informes, guías y consultas en internet (n=8).Conclusiones. Los estudios que describen el uso de preparaciones ex vivo de músculo y nervio para evaluar el efecto de neurotoxinas ofrecen un buen modelo para la caracterización del efecto presináptico y postsináptico del veneno producido por las serpientes Micrurus.

Comparación de la eficacia, la seguridad y la farmacocinética de los antivenenos antiofídicos: revisión de literatura

En Colombia se presentan anualmente alrededor de 5000 casos de mordedura de serpiente y su tratamiento se basa en la neutralización con inmunoglobulinas completas purificadas, sin embargo, globalmente se utilizan antivenenos faboterápicos. Objetivo: Dar a conocer diferencias entre las generaciones de antivenenos, la importancia del veneno en la producción de anticuerpos, comparar aspectos farmacocinéticos y los efectos adversos en pacientes. Materiales Métodos: Se realizó una búsqueda de literatura en bases de datos utilizando combinaciones de los descriptores y términos Mesh, en inglés y español. Se cotejaron parámetros farmacocinéticos en estudios preclínicos y los efectos adversos en estudios clínicos. Resultados: Se encontraron diferencias debidas al tamaño de la fracción de la inmunoglobulina que la compone, así entre más pequeña es ésta, se observa mayor distribución a los tejidos y una vida media más corta, comparada con las moléculas más pesadas. Se encontraron estudios con disminución de efectos adversos con antivenenos faboterápicos 

Contribution of endothelial cell and macrophage activation in the alterations induced by the venom of Micrurus tener tener in C57BL/6 mice

An acute inflammatory response, cellular infiltrates, anemia, hemorrhage and endogenous fibrinolysis activation were previously described in C57BL/6 mice injected with M. tener tener venom (Mtt). As the endothelium and innate immunity may participate in these disturbances and due to our poor understanding of the alterations produced by these venoms when the neurotoxic component is not predominant, we evaluated the effects in an in vitro model. At 24 h, the release of pro-inflammatory mediators was detected in peritoneal macrophages. At different times, the release of pro-inflammatory (TNF-α, IL-6, NO and E-Selectin), pro-coagulant (vWF and TF) and pro-fibrinolytic (uPA) mediators were seen in liver sinusoidal endothelial cells (LSECs). These results suggest that Mtt venom activates macrophages and endothelium, thus inducing the release of mediators, such as TNF-α, that orchestrate the acute inflammatory response and the later infiltration of mononuclear cells into liver in C57BL/6 mice. In addition, endothelium activation promotes TF expression, which may in turn modulate the inflammatory and hemostatic response. These findings suggest crosstalk between inflammation and hemostasis in the alterations observed in Micrurus envenomation, where the neurotoxic manifestations do not predominate.

Antivenom effect on lymphatic absorption and pharmacokinetics of coral snake venom using a large animal model

Context: Historically, administration and dosing of antivenom (AV) have been guided primarily by physician judgment because of incomplete understanding of the envenomation process. As demonstrated previously, lymphatic absorption plays a major role in the availability and pharmacokinetics (PK) of coral snake venom injected subcutaneously, which suggests that absorption from subcutaneous tissue is the limiting step for venom bioavailability, supporting the notion that the bite site is an ongoing venom depot. This feature may underlie the recurrence phenomena reported in viperid envenomation that appear to result from a mismatch between venom and AV PK. The role of lymphatic absorption in neutralization of venom by AV administered intravenously remains unclear. Methods: The effect of AV on systemic bioavailability and neutralization of Micrurus fulvius venom was assessed using a central lymph-cannulated sheep model. Venom was administered by subcutaneous injection in eight sheep, four with and four without thoracic duct cannulation and drainage. Two hours after venom injection, AV was administered intravenously. Venom and AV concentrations in serum and lymph were determined by ELISA assay from samples collected over a 6-h period and in tissues harvested post-mortem. Results: After AV injection, venom levels in serum fell immediately to undetectable with a subsequent increase in concentration attributable to non-toxic venom proteins. In lymph, AV became detectable 6 min after treatment; venom levels dropped concurrently but remained detectable 4 h later. Post-mortem samples from the venom injection site confirmed the presence of venom near the point of injection. Neither venom nor AV was detected at significant concentrations in major organs or contralateral skin. Conclusions: Intravenous AV immediately neutralizes venom in the bloodstream and can extravasate to neutralize venom absorbed by lymph but this neutralization seems to be slow and incomplete. Residual venom in the inoculation site demonstrates that this site functions as a depot where it is not neutralized by AV, which allows the venom to remain active with slow delivery to the bloodstream for ongoing systemic distribution.

Pro-inflammatory response and hemostatic disorder induced by venom of the coral snake Micrurus tener tener IN C57BL/6 mice

Micrurus venoms are known to induce mainly neurotoxicity in victims. However, other manifestations, including hemorrhage, edema, myotoxicity, complement activation, and hemostatic activity have been reported. In order to develop a more complete pharmacological profile of these venoms, inflammatory responses and hemostasis were evaluated in C57BL/6 mice treated with a sub-lethal dose of M. t. tener (Mtt) venom (8 μg/mouse), inoculated intraperitoneally. The venom induced moderate bleeding into the abdominal cavity and lungs, as well as infiltration of leukocytes into the liver. After 30 min, the release of pro-inflammatory mediators (TNF-α, IL-6, and NO) were observed, being most evident at 4 h. There was a decrease in hemoglobin and hematocrit levels at 72 h, a prolongation in coagulation times (PT and aPTT), a decrease in the fibrinogen concentration and an increase in fibrinolytic activity. In this animal model, it was proposed that Mtt venom induces inflammation with the release of mediators such as TNF-α, in response to the toxins. These mediators may activate hemostatic mechanisms, producing systemic fibrinolysis and hemorrhage. These findings suggest alternative treatments in Micrurus envenomations in which neurotoxic manifestations do not predominate.

The importance of species: Pygmy rattlesnake venom toxicity differs between native prey and related non-native species

Venom toxicity assessments are often based upon non-native surrogate prey species that are not consumed in the wild by the venomous predator. This raises questions about the relevance of toxicity results on these "model" prey in addressing ecological or evolutionary questions about venom effects on native prey. We explore this issue by comparing the toxicity of venom from pygmy rattlesnakes (Sistrurus miliarius) on taxonomically-diverse sets of model (non-native) and native prey. Specifically, we compared rattlesnake venom toxicity for nine species from three broad taxonomic groups of prey (reptiles, mammals, and amphibians) to determine whether estimates of venom toxicity for the non-native model species of each group was representative of species which were native prey. In all three groups, model species (Anolis sagrei, Mus musculus, and Lithobates pipiens) had a significantly different mortality response from one or more of the native prey species (Anolis carolinensis, Peromyscus gossypinus, Lithobates sphenocephalus, Hyla cinerea, and Hyla squirella) that the models were meant to represent. Two features of our results suggest an importance of evolutionary history in understanding these differences. First, there was a phylogenetic component to prey responses to venom in that in each group, non-native models and congeneric native prey showed more similar responses than prey from other genera suggesting that venom may act on common prey targets that result from common ancestry. Second, native prey generally showed higher LD₅₀ values than their non-native counterparts, suggesting greater resistance to venom from a predator with which they interact in nature. Our results suggest that researchers should use native prey to generate measures of venom toxicity that are ecologically and evolutionarily relevant. If this is not possible using "model" prey species that are close taxonomic relatives to natural prey may be a reasonable alternative.

Coralsnake Venomics: Analyses of Venom Gland Transcriptomes and Proteomes of Six Brazilian Taxa

Venom gland transcriptomes and proteomes of six Micrurus taxa (M. corallinus, M. lemniscatus carvalhoi, M. lemniscatus lemniscatus, M. paraensis, M. spixii spixii, and M. surinamensis) were investigated, providing the most comprehensive, quantitative data on Micrurus venom composition to date, and more than tripling the number of Micrurus venom protein sequences previously available. The six venomes differ dramatically. All are dominated by 2-6 toxin classes that account for 91-99% of the toxin transcripts. The M. s. spixii venome is compositionally the simplest. In it, three-finger toxins (3FTxs) and phospholipases A₂ (PLA₂s) comprise >99% of the toxin transcripts, which include only four additional toxin families at levels ≥0.1%. Micrurus l. lemniscatus venom is the most complex, with at least 17 toxin families. However, in each venome, multiple structural subclasses of 3FTXs and PLA₂s are present. These almost certainly differ in pharmacology as well. All venoms also contain phospholipase B and vascular endothelial growth factors. Minor components (0.1-2.0%) are found in all venoms except that of M. s. spixii. Other toxin families are present in all six venoms at trace levels (<0.005%). Minor and trace venom components differ in each venom. Numerous novel toxin chemistries include 3FTxs with previously unknown 8- and 10-cysteine arrangements, resulting in new 3D structures and target specificities. 9-cysteine toxins raise the possibility of covalent, homodimeric 3FTxs or heterodimeric toxins with unknown pharmacologies. Probable muscarinic sequences may be reptile-specific homologs that promote hypotension via vascular mAChRs. The first complete sequences are presented for 3FTxs putatively responsible for liberating glutamate from rat brain synaptosomes. Micrurus C-type lectin-like proteins may have 6-9 cysteine residues and may be monomers, or homo- or heterodimers of unknown pharmacology. Novel KSPIs, 3× longer than any seen previously, appear to have arisen in three species by gene duplication and fusion. Four species have transcripts homologous to the nociceptive toxin, (MitTx) α-subunit, but all six species had homologs to the β-subunit. The first non-neurotoxic, non-catalytic elapid phospholipase A₂s are reported. All are probably myonecrotic. Phylogenetic analysis indicates that the six taxa diverged 15-35 million years ago and that they split from their last common ancestor with Old World elapines nearly 55 million years ago. Given their early diversification, many cryptic micrurine taxa are anticipated.

Strategies in 'snake venomics' aiming at an integrative view of compositional, functional, and immunological characteristics of venoms

This work offers a general overview on the evolving strategies for the proteomic analysis of snake venoms, and discusses how these may be combined through diverse experimental approaches with the goal of achieving a more comprehensive knowledge on the compositional, toxic, and immunological characteristics of venoms. Some recent developments in this field are summarized, highlighting how strategies have evolved from the mere cataloguing of venom components (proteomics/venomics), to a broader exploration of their immunological (antivenomics) and functional (toxicovenomics) characteristics. Altogether, the combination of these complementary strategies is helping to build a wider, more integrative view of the life-threatening protein cocktails produced by venomous snakes, responsible for thousands of deaths every year.

Venomics: integrative venom proteomics and beyond*

Venoms are integrated phenotypes that evolved independently in, and are used for predatory and defensive purposes by, a wide phylogenetic range of organisms. The same principles that contribute to the evolutionary success of venoms, contribute to making the study of venoms of great interest in such diverse fields as evolutionary ecology and biotechnology. Evolution is profoundly contingent, and nature also reinvents itself continuosly. Changes in a complex phenotypic trait, such as venom, reflect the influences of prior evolutionary history, chance events, and selection. Reconstructing the natural history of venoms, particularly those of snakes, which will be dealt with in more detail in this review, requires the integration of different levels of knowledge into a meaningful and comprehensive evolutionary framework for separating stochastic changes from adaptive evolution. The application of omics technologies and other disciplines have contributed to a qualitative and quantitative advance in the road map towards this goal. In this review we will make a foray into the world of animal venoms, discuss synergies and complementarities of the different approaches used in their study, and identify current bottlenecks that prevent inferring the evolutionary mechanisms and ecological constraints that molded snake venoms to their present-day variability landscape.

Heterologous expression, protein folding and antibody recognition of a neurotoxin from the Mexican coral snake Micrurus laticorallis

Background

The cysteine-rich neurotoxins from elapid venoms are primarily responsible for human and animal envenomation; however, their low concentration in the venom may hamper the production of efficient elapid antivenoms. Therefore, the aim of the present study was to produce fully active elapid neurotoxic immunogens for elapid antivenom production.

Method

Cysteine-rich neurotoxins showed recombinant expression in two strains of E. coli, and were purified using affinity chromatography and reverse-phase HPLC (rpHPLC).

Results

The cDNA of the four disulfide-bridged peptide neurotoxin Mlat1 was cloned into a modified expression vector, pQE30, which was transfected into two different E. coli strains. The recombinant toxin (HisrMlat1) was found only in inclusion bodies in M15 strain cells, and in both inclusion bodies and cytoplasm in Origami strain cells. The HisrMlat1 from inclusion bodies from M15 cells was solubilized using guanidine hydrochloride, and then purified by rpHPLC. It showed various contiguous fractions having the same molecular mass, indicating that HisrMlat1 was oxidized after cell extraction forming different misfolded disulfide bridge arrangements without biological activity. In vitro folding conditions of the misfolded HisrMlat1 generated a biologically active HisrMlat1. On the other hand, the HisrMlat1 from the cytoplasm from Origami cells was already soluble, and then purified by HPLC. It showed a single fraction with neurotoxic activity; so, no folding steps were needed. The in vitro folded HisrMlat1 from M15 cells and the cytoplasmic soluble HisrMlat1from Origami cells were indistinguishable in their structure and neurotoxicity. Rabbit polyclonal antibodies raised up against biologically active HisrMlat1 recognized the native Mlat1 (nMlat1) from the whole venom of M. laticorallis. In addition, HisrMlat1 was recognized by horse polyclonal antibodies obtained from the immunization of elapid species from sub-Saharan Africa.

Conclusion

HisrMlat1 shows increased biological activities compared to the native peptide, and may be used as an immunizing agent in combination with other toxic components such phospholipases type A2 for elapid antivenom production.

Venomic Analysis of the Poorly Studied Desert Coral Snake, Micrurus tschudii tschudii, Supports the 3FTx/PLA₂ Dichotomy across Micrurus Venoms

The venom proteome of the poorly studied desert coral snake Micrurus tschudii tschudii was unveiled using a venomic approach, which identified ≥38 proteins belonging to only four snake venom protein families. The three-finger toxins (3FTxs) constitute, both in number of isoforms (~30) and total abundance (93.6% of the venom proteome), the major protein family of the desert coral snake venom. Phospholipases A₂ (PLA₂s; seven isoforms, 4.1% of the venom proteome), 1–3 Kunitz-type proteins (1.6%), and 1–2 l-amino acid oxidases (LAO, 0.7%) complete the toxin arsenal of M. t. tschudii. Our results add to the growing evidence that the occurrence of two divergent venom phenotypes, i.e., 3FTx- and PLA₂-predominant venom proteomes, may constitute a general trend across the cladogenesis of Micrurus. The occurrence of a similar pattern of venom phenotypic variability among true sea snake (Hydrophiinae) venoms suggests that the 3FTx/PLA₂ dichotomy may be widely distributed among Elapidae venoms.

Venom of the Coral Snake Micrurus clarki: Proteomic Profile, Toxicity, Immunological Cross-Neutralization, and Characterization of a Three-Finger Toxin

Micrurus clarki is an uncommon coral snake distributed from the Southeastern Pacific of Costa Rica to Western Colombia, for which no information on its venom could be found in the literature. Using a ‘venomics’ approach, proteins of at least nine families were identified, with a moderate predominance of three-finger toxins (3FTx; 48.2%) over phospholipase A₂ (PLA₂; 36.5%). Comparison of this venom profile with those of other Micrurus species suggests that it may represent a more balanced, ‘intermediate’ type within the dichotomy between 3FTx- and PLA₂-predominant venoms. M. clarki venom was strongly cross-recognized and, accordingly, efficiently neutralized by an equine therapeutic antivenom against M. nigrocinctus, revealing their high antigenic similarity. Lethal activity for mice could be reproduced by a PLA₂ venom fraction, but, unexpectedly, not by fractions corresponding to 3FTxs. The most abundant venom component, hereby named clarkitoxin-I, was identified as a short-chain (type I) 3FTx, devoid of lethal effect in mice, whose target remains to be defined. Its amino acid sequence of 66 residues shows high similarity with predicted sequences of venom gland transcripts described for M. fulvius, M. browni, and M. diastema.

Integrative characterization of the venom of the coral snake Micrurus dumerilii (Elapidae) from Colombia: Proteome, toxicity, and cross-neutralization by antivenom

In Colombia, nearly 2.8% of the 4200 snakebite accidents recorded annually are inflicted by coral snakes (genus Micrurus). Micrurus dumerilii has a broad distribution in this country, especially in densely populated areas. The proteomic profile of its venom was here studied by a bottom-up approach combining RP-HPLC, SDS-PAGE and MALDI-TOF/TOF. Venom proteins were assigned to eleven families, the most abundant being phospholipases A2 (PLA2; 52.0%) and three-finger toxins (3FTx; 28.1%). This compositional profile shows that M. dumerilii venom belongs to the 'PLA2-rich' phenotype, in the recently proposed dichotomy for Micrurus venoms. Enzymatic and toxic venom activities correlated with protein family abundances. Whole venom induced a conspicuous myotoxic, cytotoxic and anticoagulant effect, and was mildly edematogenic and proteolytic, whereas it lacked hemorrhagic activity. Some 3FTxs and PLA2s reproduced the lethal effect of venom. A coral snake antivenom to Micrurus nigrocinctus demonstrated significant cross-recognition of M. dumerilii venom proteins, and accordingly, ability to neutralize its lethal effect. The combined compositional, functional, and immunological data here reported for M. dumerilii venom may contribute to a better understanding of these envenomings, and support the possible use of anti-M. nigrocinctus coral snake antivenom in their treatment.

BIOLOGICAL SIGNIFICANCE

Coral snakes represent a highly diversified group of elapids in the New World, with nearly 70 species within the genus Micrurus. Owing to their scarce yields, the biochemical composition and toxic activities of coral snake venoms have been less well characterized than those of viperid species. In this work, an integrative view of the venom of M. dumerilii, a medically relevant coral snake from Colombia, was obtained by a combined proteomic, functional, and immunological approach. The venom contains proteins from at least eleven families, with a predominance of phospholipases A2 (PLA2), followed by three-finger toxins (3FTx). According to its compositional profile, M. dumerilii venom can be grouped with those of several Micrurus species from North and Central America that present a PLA2-predominant phenotype, to date it is the most southerly coral snake species to do so. Other coral snake species that a 'PLA2-rich' venom, M. dumerilii venom contains both components that form MitTx, a pain-inducing heterodimeric complex recently characterized from the venom of Micrurus tener, also present in Micrurus mosquitensis and M. nigrocinctus venoms. In addition to a lethal three-finger toxin, PLA2s participate in the toxicity of M. dumerilii venom, some of them displaying ability to induce cytolysis, muscle necrosis, and lethality to mice. An antivenom to M. nigrocinctus demonstrated significant cross-recognition of M. dumerilii venom proteins, and accordingly, ability to neutralize its lethal effect, being of potential therapeutic usefulness in these envenomings.

Neurotoxic snakes of the Americas

Snake envenomation is a global problem and often a matter of life or death. Emergency treatment is not always readily available or effective. There are numerous neurotoxic snakes in the Americas, chiefly elapids; some crotalids have also evolved neurotoxic venom. The variability of neurotoxins found in snake venom within the same species makes development and choice of proper antivenom a major challenge that has not been completely addressed. This article reviews the epidemiology, clinical effects, and current treatment of neurotoxic snake envenomation in the Americas.

Snake venomics of Micrurus alleni and Micrurus mosquitensis from the Caribbean region of Costa Rica reveals two divergent compositional patterns in New World elapids

Protein composition, toxicity, and neutralization of the venoms of Micrurus alleni and Micrurus mosquitensis, two sympatric monadal coral snakes found in humid environments of the Caribbean region of Costa Rica, were studied. Proteomic profiling revealed that these venoms display highly divergent compositions: the former dominated by three-finger toxins (3FTx) and the latter by phospholipases A2 (PLA2). Protein family abundances correlated with enzymatic and toxic characteristics of the venoms. Selective inhibition experiments showed that PLA2s play only a marginal role in the lethal effect of M. alleni venom, but have a major role in M. mosquitensis venom. Proteomic data gathered from other Micrurus species evidenced that the two divergent venom phenotypes are recurrent, and may constitute a general trend across New World elapids. Further, M. mosquitensis, but not M. alleni, venom contains PLA2-like/Kunitz-type inhibitor complex(es) that resemble the ASIC1a/2-activating MitTx heterodimeric toxin isolated from Micrurus tener venom. The evolutionary origin and adaptive relevance of the puzzling phenotypic variability of Micrurus venoms remain to be understood. An antivenom against the PLA2-predominant Micrurus nigrocinctus venom strongly cross-recognized and neutralized M. mosquitensis venom, but only weakly M. alleni venom.

Next-generation snake venomics: protein-locus resolution through venom proteome decomplexation

Venom research has been continuously enhanced by technological advances. High-throughput technologies are changing the classical paradigm of hypothesis-driven research to technology-driven approaches. However, the thesis advocated in this paper is that full proteome coverage at locus-specific resolution requires integrating the best of both worlds into a protocol that includes decomplexation of the venom proteome prior to liquid chromatography-tandem mass spectrometry matching against a species-specific transcriptome. This approach offers the possibility of proof-checking the species-specific contig database using proteomics data. Immunoaffinity chromatography constitutes the basis of an antivenomics workflow designed to quantify the extent of cross-reactivity of antivenoms against homologous and heterologous venom toxins. In the author's view, snake venomics and antivenomics form part of a biology-driven conceptual framework to unveil the genesis and natural history of venoms, and their within- and between-species toxicological and immunological divergences and similarities. Understanding evolutionary trends across venoms represents the Rosetta Stone for generating broad-ranging polyspecific antivenoms.

Eastern coral snake Micrurus fulvius venom toxicity in mice is mainly determined by neurotoxic phospholipases A2

Here we show for the first time that the venom from an elapid (Micrurus fulvius) contains three finger toxin (3FTxs) peptides with low toxicity but high content of lethal phospholipases A2 (PLA2). The intravenous venom LD50 in mice was 0.3μg/g. Fractionation on a C18 column yielded 22 fractions; in terms of abundance, 58.3% of them were components of 13-14kDa and 24.9% were molecules of 6-7kDa. Two fractions with PLA2 activity represented 33.4% of the whole venom and were the most lethal fractions. Fractions with low molecular mass (<7000Da) partially and reversibly blocked the nicotinic acetylcholine receptor (nAChR), with the exception of one that blocked it completely. The fraction that blocked 100% contained two protein species whose dose-response was determined; the IC50s were 13±1 and 9.5±0.3nM. Despite the apparent effect on nAChR none of the low molecular mass fractions were lethal in mice, at concentrations of 1μg/g. From 2D-PAGE and LC-MS/MS, we identified fourteen species of PLA2, four protein species of C-type lectin, three zinc metalloproteinases, one phosphodiesterase and one 3FTx. The N-terminal amino acid sequence of fractions with biological interest was obtained.

BIOLOGICAL SIGNIFICANCE

In contrast with coral snake venoms from South America, M. fulvius has minor amounts of low molecular mass components, but high content of PLA2, which is responsible for the venom lethality of this species. The results reported here contribute to better understanding of envenomation development and to improve antivenom design and production. These findings break from the paradigm that neurotoxicity caused by Micrurus venoms is mainly attributable to 3FTx neurotoxins and encourage future studies on Micrurus evolution and venom specialization. This article is part of a Special Issue entitled Non-model organisms.

Venomous snakes of Costa Rica: biological and medical implications of their venom proteomic profiles analyzed through the strategy of snake venomics

In spite of its small territory of ~50,000km(2), Costa Rica harbors a remarkably rich biodiversity. Its herpetofauna includes 138 species of snakes, of which sixteen pit vipers (family Viperidae, subfamily Crotalinae), five coral snakes (family Elapidae, subfamily Elapinae), and one sea snake (Family Elapidae, subfamily Hydrophiinae) pose potential hazards to human and animal health. In recent years, knowledge on the composition of snake venoms has expanded dramatically thanks to the development of increasingly fast and sensitive analytical techniques in mass spectrometry and separation science applied to protein characterization. Among several analytical strategies to determine the overall protein/peptide composition of snake venoms, the methodology known as 'snake venomics' has proven particularly well suited and informative, by providing not only a catalog of protein types/families present in a venom, but also a semi-quantitative estimation of their relative abundances. Through a collaborative research initiative between Instituto de Biomedicina de Valencia (IBV) and Instituto Clodomiro Picado (ICP), this strategy has been applied to the study of venoms of Costa Rican snakes, aiming to obtain a deeper knowledge on their composition, geographic and ontogenic variations, relationships to taxonomy, correlation with toxic activities, and discovery of novel components. The proteomic profiles of venoms from sixteen out of the 22 species within the Viperidae and Elapidae families found in Costa Rica have been reported so far, and an integrative view of these studies is hereby presented. In line with other venomic projects by research groups focusing on a wide variety of snakes around the world, these studies contribute to a deeper understanding of the biochemical basis for the diverse toxic profiles evolved by venomous snakes. In addition, these studies provide opportunities to identify novel molecules of potential pharmacological interest. Furthermore, the establishment of venom proteomic profiles offers a fundamental platform to assess the detailed immunorecognition of individual proteins/peptides by therapeutic or experimental antivenoms, an evolving methodology for which the term 'antivenomics' was coined (as described in an accompanying paper in this special issue).

BIOLOGICAL SIGNIFICANCE

Venoms represent an adaptive trait and an example of both divergent and convergent evolution. A deep understanding of the composition of venoms and of the principles governing the evolution of venomous systems is of applied importance for exploring the enormous potential of venoms as sources of chemical and pharmacological novelty but also to fight the consequences of snakebite envenomings. Key to this is the identification of evolutionary and ecological trends at different taxonomical levels. However, the evolution of venomous species and their venoms do not always follow the same course, and the identification of structural and functional convergences and divergences among venoms is often unpredictable by a phylogenetic hypothesis. Snake venomics is a proteomic-centered strategy to deconstruct the complex molecular phenotypes the venom proteomes. The proteomic profiles of venoms from sixteen out of the 22 venomous species within the Viperidae and Elapidae families found in Costa Rica have been completed so far. An integrative view of their venom composition, including the identification of geographic and ontogenic variations, is hereby presented. Venom proteomic profiles offer a fundamental platform to assess the detailed immunorecognition of individual venom components by therapeutic or experimental antivenoms. This aspect is reviewed in the companion paper. This article is part of a Special Issue entitled: Proteomics of non-model organisms.