Toxicovenomics and antivenom profiling of the Eastern green mamba snake (Dendroaspis angusticeps)

Absolute venomics: Absolute quantification of intact venom proteins through elemental mass spectrometry

We report the application of a hybrid element and molecular MS configuration for the parallel absolute quantification of μHPLC-separated intact sulfur-containing venom proteins, via ICP triple quadrupole MS and ³²S/³⁴S isotope dilution analysis, and identification by ESI-QToF-MS of the toxins of the medically important African black-necked spitting cobra, Naja nigricollis (Tanzania); New Guinea small-eyed snake, Micropechis ikaheka; and Papuan black snake, Pseudechis papuanus. The main advantage of this approach is that only one generic sulfur-containing standard is required to quantify each and all intact Cys- and/or Met-containing toxins of the venom proteome. The results of absolute quantification are in reasonably good agreement with previously reported relative quantification of the most abundant protein families. However, both datasets depart in the quantification of the minor ones, showing a tendency for this set of proteins to be underestimated in standard peptide-centric venomics approaches. The molecular identity, specific toxic activity, and concentration in the venom, are the pillars on which the toxicovenomics-aimed discovery of the most medically-relevant venom toxins, e.g. those that need to be neutralized by an effective therapeutic antivenom, should be based. The pioneering venom proteome-wide absolute quantification shown in this paper represents thus a significant advance towards this goal. The potential of ICP triple quadrupole MS in proteomics in general, and venomics in particular, is critically discussed.

BIOLOGICAL SIGNIFICANCE

Animal venoms provide excellent model systems for investigating interactions between predators and prey, and the molecular mechanisms that contribute to adaptive protein evolution. On the other hand, numerous cases of snake bites occur yearly by encounters of humans and snakes in their shared natural environment. Snakebite envenoming is a serious global public health issue that affects the most impoverished and geopolitically disadvantaged rural communities in many tropical and subtropical countries. Unveiling the temporal and spatial patterns of venom variability is of fundamental importance to understand the molecular basis of envenoming, a prerequisite for developing therapeutic strategies against snakebite envenoming. Research on venoms has been continuously enhanced by advances in technology. The combined application of next-generation transcriptomic and venomic workflows has demonstrated unparalleled capabilities for venom characterization in unprecedented detail. However, mass spectrometry is not inherently quantitative, and this analytical limitation has sparked the development of methods to determine absolute abundance of proteins in biological samples. Here we show the potential of a hybrid element and molecular MS configuration for the parallel ESI-QToF-MS and ICP-QQQ detection and absolute quantification of intact sulfur-containing venom proteins via ³²S/³⁴S isotope dilution analysis. This configuration has been applied to quantify the toxins of the medically important African snake Naja nigricollis (Tanzania), and the Papuan species Micropechis ikaheka and Pseudechis papuanus.

Protein-species quantitative venomics: looking through a crystal ball

In this paper we discuss recent significant developments in the field of venom research, specifically the emergence of top-down proteomic applications that allow achieving compositional resolution at the level of the protein species present in the venom, and the absolute quantification of the venom proteins (the term “protein species” is used here to refer to all the different molecular forms in which a protein can be found. Please consult the special issue of Jornal of Proteomics “Towards deciphering proteomes via the proteoform, protein speciation, moonlighting and protein code concepts” published in 2016, vol. 134, pages 1-202). Challenges remain to be solved in order to achieve a compact and automated platform with which to routinely carry out comprehensive quantitative analysis of all toxins present in a venom. This short essay reflects the authors’ view of the immediate future in this direction for the proteomic analysis of venoms, particularly of snakes.

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.

The three-finger toxin fold: a multifunctional structural scaffold able to modulate cholinergic functions

Three-finger fold toxins are miniproteins frequently found in Elapidae snake venoms. This fold is characterized by three distinct loops rich in β-strands and emerging from a dense, globular core reticulated by four highly conserved disulfide bridges. The number and diversity of receptors, channels, and enzymes identified as targets of three-finger fold toxins is increasing continuously. Such manifold diversity highlights the specific adaptability of this fold for generating pleiotropic functions. Although this toxin superfamily disturbs many biological functions by interacting with a large diversity of molecular targets, the most significant target is the cholinergic system. By blocking the activity of the nicotinic and muscarinic acetylcholine receptors or by inhibiting the enzyme acetylcholinesterase, three-finger fold toxins interfere most drastically with neuromuscular junction functioning. Several of these toxins have become powerful pharmacological tools for studying the function and structure of their molecular targets. Most importantly, since dysfunction of these receptors/enzyme is involved in many diseases, exploiting the three-finger scaffold to create novel, highly specific therapeutic agents may represent a major future endeavor. This is an article for the special issue XVth International Symposium on Cholinergic Mechanisms.

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.

What killed Karl Patterson Schmidt? Combined venom gland transcriptomic, venomic and antivenomic analysis of the South African green tree snake (the boomslang), Dispholidus typus

Background

Non-front-fanged colubroid snakes comprise about two-thirds of extant ophidian species. The medical significance of the majority of these snakes is unknown, but at least five species have caused life-threatening or fatal human envenomings. However, the venoms of only a small number of species have been explored.

Methods

A combined venomic and venom gland transcriptomic approach was employed to characterise of venom of Dispholidus typus (boomslang), the snake that caused the tragic death of Professor Karl Patterson Schmidt. The ability of CroFab™ antivenom to immunocapture boomslang venom proteins was investigated using antivenomics.

Results

Transcriptomic-assisted proteomic analysis identified venom proteins belonging to seven protein families: three-finger toxin (3FTx); phospholipase A₂ (PLA₂); cysteine-rich secretory proteins (CRISP); snake venom (SV) serine proteinase (SP); C-type lectin-like (CTL); SV metalloproteinases (SVMPs); and disintegrin-like/cysteine-rich (DC) proteolytic fragments. CroFab™ antivenom efficiently immunodepleted some boomslang SVMPs.

Conclusions

The present work is the first to address the overall proteomic profile of D. typus venom. This study allowed us to correlate the toxin composition with the toxic activities of the venom. The antivenomic analysis suggested that the antivenom available at the time of the unfortunate accident could have exhibited at least some immunoreactivity against the boomslang SVMPs responsible for the disseminated intravascular coagulation syndrome that caused K.P. Schmidt's fatal outcome.

General significance

This study may stimulate further research on other non-front-fanged colubroid snake venoms capable of causing life-threatening envenomings to humans, which in turn should contribute to prevent fatal human accidents, such as that unfortunately suffered by K.P. Schmidt.

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The venom proteome of Dispholidus typus (boomslang) is reported.

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Transcriptomic-assisted proteomic analysis identified venom proteins belonging to seven protein families.

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Boomslang venom proteome is dominated (75%) by snake venom PIII-metalloproteinases (PIII-SVMPs).

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CroFab™ antivenom efficiently immunodepleted some boomslang PIII-SVMPs.

High-throughput immuno-profiling of mamba (Dendroaspis) venom toxin epitopes using high-density peptide microarrays

Snakebite envenoming is a serious condition requiring medical attention and administration of antivenom. Current antivenoms are antibody preparations obtained from the plasma of animals immunised with whole venom(s) and contain antibodies against snake venom toxins, but also against other antigens. In order to better understand the molecular interactions between antivenom antibodies and epitopes on snake venom toxins, a high-throughput immuno-profiling study on all manually curated toxins from Dendroaspis species and selected African Naja species was performed based on custom-made high-density peptide microarrays displaying linear toxin fragments. By detection of binding for three different antivenoms and performing an alanine scan, linear elements of epitopes and the positions important for binding were identified. A strong tendency of antivenom antibodies recognizing and binding to epitopes at the functional sites of toxins was observed. With these results, high-density peptide microarray technology is for the first time introduced in the field of toxinology and molecular details of the evolution of antibody-toxin interactions based on molecular recognition of distinctive toxic motifs are elucidated.

Elemental Mass Spectrometry for Absolute Intact Protein Quantification without Protein-Specific Standards: Application to Snake Venomics

Absolute protein quantification methods based on molecular mass spectrometry usually require stable isotope-labeled analogous standards for each target protein or peptide under study, which in turn must be certified using natural standards. In this work, we report a direct and accurate methodology based on capLC-ICP-QQQ and online isotope dilution analysis for the absolute and sensitive quantification of intact proteins. The combination of the postcolumn addition of ³⁴S and a generic S-containing internal standard spiked to the sample provides full compound independent detector response and thus protein quantification without the need for specific standards. Quantitative recoveries, using a chromatographic core-shell C4 column for the various protein species assayed were obtained (96-100%). Thus, the proposed strategy enables the accurate quantification of proteins even if no specific standards are available for them. In addition, to the best of our knowledge, we obtained the lowest detection limits reported in the quantitative analysis of intact proteins by direct measurement of sulfur with ICPMS (358 fmol) and protein (ranging from 7 to 15 fmol depending on the assayed protein). The quantitative results for individual and simple mixtures of model proteins were statistically indistinguishable from the manufacturer's values. Finally, the suitability of the strategy for real sample analysis (including quantitative protein recovery from the column) was illustrated for the individual absolute quantification of the proteins and whole protein content in a venom sample. Parallel capLC-ESI-QTOF analysis was employed to identify the proteins, a prerequisite to translate the mass of quantified S for each chromatographic peak into individual protein mass.

Top-down venomics of the East African green mamba, Dendroaspis angusticeps, and the black mamba, Dendroaspis polylepis, highlight the complexity of their toxin arsenals

We report the characterization, by combination of high-resolution on-line molecular mass and disulfide bond profiling and top-down MS/MS analysis, of the venom proteomes of two congeneric African snake species of medical importance, Dendroaspis angusticeps (green mamba) and D. polylepis (black mamba). Each of these mamba venoms comprised more than two-hundred polypeptides belonging to just a few toxin families. Both venom proteomes are overwhelmingly composed of post-synaptically-acting short- and long-chain neurotoxins that potently inhibit muscle- and neuronal-type nicotinic acetylcholine receptors; muscarinic cardiotoxins; and dendrotoxins, that block some of the Kv1, n-class of K+ channels. However, the identity of the major proteins and their relative abundances exhibit marked interspecific variation. In addition, the greater resolution of the top-down venomic analytical approach revealed previously undetected protein species, isoforms and proteoforms, including the identification and precise location of modified lysine residues in a number of proteins in both venoms, but particularly in green mamba toxins. This comparative top-down venomic analysis unveiled the untapped complexity of Dendroaspis venoms and lays the foundations for rationalizing the notably different potency of green and black mamba lethal arsenals at locus resolution.

SIGNIFICANCE PARAGRAPH

We report the characterization, by combination of high-resolution on-line molecular mass and disulfide bond profiling and top-down MS/MS analysis, of the venom proteomes of two congeneric African snake species of medical importance, Dendroaspis angusticeps (green mamba) and D. polylepis (black mamba). Each of these mamba venoms comprised more than two-hundred polypeptides belonging to just a few toxin families. Both venom proteomes are overwhelmingly composed of post-synaptically-acting short- and long-chain neurotoxins that potently inhibit muscle- and neuronal-type nicotinic acetylcholine receptors; muscarinic cardiotoxins; and dendrotoxins, that block some of the Kv1, n-class of K+ channels. However, the identity of the major proteins and their relative abundances exhibit marked interspecific variation. In addition, the greater resolution of the top-down venomic analytical approach revealed previously undetected protein species, isoforms and proteoforms, including the identification and precise location of modified lysine residues in a number of proteins in both venoms, but particularly in green mamba toxins. This comparative top-down venomic analysis unveiled the untapped complexity of Dendroaspis venoms and lays the foundations for rationalizing the notably different potency of green and black mamba lethal arsenals at locus resolution.

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.