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

Hyperpolarization Modulation of the T-Type hCav3.2 Channel by Human Synenkephalin [1-53], a Shrew Neurotoxin Analogue without Paralytic Effects

Mammalian secreted venoms mainly consist of peptides and proteases used for defense or predation. Blarina paralytic peptides (BPPs), mealworm-targeting neurotoxins from shrew, are very similar to human synenkephalin. This peptide is released from proenkephalin in the brain along with opioid peptides that mediate analgesic and antidepressant effects, though its physiological function is unclear. Here, we synthesized and characterized human synenkephalin [1-53] (hSYN) and reveal its disulfide bond connectivity. Similar to BPP2, hSYN caused a hyperpolarizing shift in the human T-type voltage-gated calcium channel (hCav3.2) at 0.74 µM, but did not paralyze mealworms. Molecular docking and molecular dynamics simulations showed that hSYN and BPP2 interact with hCav3.2 channel differently, due to differences in polar residues. Since Cav3.2 channel regulates neuronal excitability and is implicated in conditions like autism and epilepsy, our findings on hSYN could provide insight into the channel gating and agonistic mechanisms, along with potential pathways for developing treatments for neurological disorders.

The Venom of Vipera ammodytes ammodytes: Proteomics, Neurotoxic Effect and Neutralization by Antivenom

Deep proteomic analyses identified, in total, 159 master proteins (with 1% FDR and 2 unique peptides) from 26 protein families in the venom of Vipera ammodytes ammodytes (Vaa). Data are available via ProteomeXchange with the identifier PXD056495. The relative abundance of PLA2s is 11.60% of the crude venom, of which 4.35% are neurotoxic Ammodytoxins (Atxs). The neurotoxicity of the venom of Vaa and the neutralizing effect of the antivenom were tested on the neuromuscular preparation of the diaphragm (NPD) of rats. The activity of PLA2 in the venom of Vaa and its neutralization by the antivenom were determined under in vitro conditions. The Vaa venom leads to a progressive decrease in NPD contractions. We administered pre-incubated venom/antivenom mixtures at various ratios of 1:2, 1:10 and 1:20 (w/w) and observed the effects of these mixtures on NPD contractions. The results show that the mean effective time (ET50) for NPD contractions with the 1:20 mixture is highly significantly different (p < 0.001) from the ET50 for the venom and the ET50 for the 1:2 and 1:10 mixture ratios. We also found a highly significant (p < 0.001) reduction in Na+/K+-ATPase activity in the NPD under the influence of the venom. The reduction in the activity of this enzyme was reversible by the antivenom. Under in vitro conditions, we have achieved the complete neutralization of PLA2 by the antivenom. In conclusion, the antivenom abolished the venom-induced progressive decrease in NPD contractions in a concentration-dependent manner. Antivenom with approximately the same mass proportion almost completely restores Na+/K+-ATPase activity in the NPD and completely neutralizes the PLA2 activity of the venom in vitro.

Potential Biotechnological Applications of Venoms from the Viperidae Family in Central America for Thrombosis

Central America is home to one of the most abundant herpetofauna in the Americas, occupying only 7% of the continent's total area. Vipers and lizards are among the most relevant venomous animals in medical practice due to the consequences of envenomation from the bite of these animals. A great diversity of biomolecules with immense therapeutic and biotechnological value is contained in their venom. This paper describes the prominent leading representatives of the family Viperidae, emphasizing their morphology, distribution, habitat, feeding, and venom composition, as well as the biotechnological application of some isolated components from the venom of the animals from these families, focusing on molecules with potential anti-thrombotic action. We present the leading protein families that interfere with blood clotting, platelet activity, or the endothelium pro-thrombotic profile. In conclusion, Central America is an endemic region of venomous animals that can provide many molecules for biotechnological applications.

De Novo Assembly of Venom Gland Transcriptome of Tropidolaemus wagleri (Temple Pit Viper, Malaysia) and Insights into the Origin of Its Major Toxin, Waglerin

The venom proteome of Temple Pit Viper (Tropidolaemus wagleri) is unique among pit vipers, characterized by a high abundance of a neurotoxic peptide, waglerin. To further explore the genetic diversity of its toxins, the present study de novo assembled the venom gland transcriptome of T. wagleri from west Malaysia. Among the 15 toxin gene families discovered, gene annotation and expression analysis reveal the dominating trend of bradykinin-potentiating peptide/angiotensin-converting enzyme inhibitor-C-type natriuretic peptide (BPP/ACEI-CNP, 76.19% of all-toxin transcription) in the transcriptome, followed by P-III snake venom metalloproteases (13.91%) and other toxins. The transcript TwBNP01 of BPP/ACEI-CNP represents a large precursor gene (209 amino acid residues) containing the coding region for waglerin (24 residues). TwBNP01 shows substantial sequence variations from the corresponding genes of its sister species, Tropidolaemus subannulatus of northern Philippines, and other viperid species which diversely code for proline-rich small peptides such as bradykinin-potentiating peptides (BPPs). The waglerin/waglerin-like peptides, BPPs and azemiopsin are proline-rich, evolving de novo from multiple highly diverged propeptide regions within the orthologous BPP/ACEI-CNP genes. Neofunctionalization of the peptides results in phylogenetic constraints consistent with a phenotypic dichotomy, where Tropidolaemus spp. and Azemiops feae convergently evolve a neurotoxic trait while vasoactive BPPs evolve only in other species.

Venomics of the milos viper (Macrovipera schweizeri) unveils patterns of venom composition and exochemistry across blunt-nosed viper venoms

Introduction: Snakebite is a neglected tropical disease and a globally important driver of death and morbidity. Vipers of the genus Macrovipera (Viperidae: Viperinae) are among the snakes of higher medical importance in the Old World. Despite the medical relevance of Macrovipera venoms, the knowledge regarding them is heterogeneously distributed with virtually all works conducted so far focusing on subspecies of Macrovipera lebetinus, while other species within the genus are largely overlooked. Here we present the first proteomic evaluation of the venom from the Greek endemic Milos viper (Macrovipera schweizeri). In line with clinical symptoms typically elicited by Macrovipera envenomations, Milos viper venom primarily comprises coagulotoxic and cytotoxic protein families, such as metalloproteinases (svMP) and serine proteases (svSP). Methods: We conducted comparative bioactivity assays on venoms from M. schweizeri and the M. lebetinus subspecies M. lebetinus cernovi, M. lebetinus obtusa, and M. lebetinus turanica, and showed that they all exhibit similarities in levels of cytotoxicity proteolytic activity, and inhibition of prokaryotic growth. Lastly, we compared Macrovipera venom profiles by 1D-SDS-PAGE and RP-HPLC, as well as our proteomic data with previously published Macrovipera venom proteomes. Results and discussion: The analyzes performed to reveal that a general venom profile seems to be conserved across blunt-nosed vipers, and that, M. schweizeri envenomations, similarly to those caused by other blunt-nosed vipers, are able to cause significant tissue damage. The present work represents an important starting point for the development of comparative studies across the full taxonomic range of the genus Macrovipera and can potentially help optimize the treatment of envenomations caused by M. schweizeri.

Effects on cell cycle progression and cytoskeleton organization of five Bothrops spp. venoms in cell culture-based assays

Snake envenomation is a neglected tropical disease. In Brazil, the Bothrops genus is responsible for about 86% of snakebite accidents. Despite extensive evidence of the cytotoxicity of snake venoms, the cellular and molecular mechanisms involved are not fully understood, especially regarding the effects on cell cycle progression and cytoskeleton organization. Traditionally, the effectiveness and quality control tests of venoms and antivenoms are assessed by in vivo assays. Despite this, there is a rising effort to develop surrogate in vitro models according to the 3R principle (Replacement, Reduction, and Refinement). In this study, we treated rat liver cells (BRL-3A) with venoms from five Bothrops species (B. jararaca, B. jararacussu, B. moojeni, B. alternatus, and B. neuwiedi) and analyzed cell viability and IC50 by MTT assay, cell cycle phases distribution by flow cytometry, and morphology and cytoskeleton alterations by immunofluorescence. In addition, we evaluated the correlation between IC50 and the enzymatic and biological activities of each venom. Our results indicated that Bothrops spp. venoms decreased the cell viability of rat liver BRL-3A cells. The rank order of potency was B. jararacussu > B. moojeni > B. alternatus > B. jararaca > B. neuwiedi. The mechanisms of cytotoxicity were related to microtubules and actin network disruption, but not to cell cycle arrest. No clear correlation was found between the IC50 and retrieved literature data of in vitro enzymatic and in vivo biological activities. This work contributed to understanding cellular and molecular mechanisms underlying the Bothrops spp. venom cytotoxicity, which can help to improve envenomation treatment, as well as disclose potential therapeutic properties of snake venoms.

A current perspective on snake venom composition and constituent protein families

Snake venoms are heterogeneous mixtures of proteins and peptides used for prey subjugation. With modern proteomics there has been a rapid expansion in our knowledge of snake venom composition, resulting in the venom proteomes of 30% of vipers and 17% of elapids being characterised. From the reasonably complete proteomic coverage of front-fanged snake venom composition (179 species-68 species of elapids and 111 species of vipers), the venoms of vipers and elapids contained 42 different protein families, although 18 were only reported in < 5% of snake species. Based on the mean abundance and occurrence of the 42 protein families, they can be classified into 4 dominant, 6 secondary, 14 minor, and 18 rare protein families. The dominant, secondary and minor categories account for 96% on average of a snake's venom composition. The four dominant protein families are: phospholipase A₂ (PLA₂), snake venom metalloprotease (SVMP), three-finger toxins (3FTx), and snake venom serine protease (SVSP). The six secondary protein families are: L-amino acid oxidase (LAAO), cysteine-rich secretory protein (CRiSP), C-type lectins (CTL), disintegrins (DIS), kunitz peptides (KUN), and natriuretic peptides (NP). Venom variation occurs at all taxonomic levels, including within populations. The reasons for venom variation are complex, as variation is not always associated with geographical variation in diet. The four dominant protein families appear to be the most important toxin families in human envenomation, being responsible for coagulopathy, neurotoxicity, myotoxicity and cytotoxicity. Proteomic techniques can be used to investigate the toxicological profile of a snake venom and hence identify key protein families for antivenom immunorecognition.

A Review of the Proteomic Profiling of African Viperidae and Elapidae Snake Venoms and Their Antivenom Neutralisation

Snakebite envenoming is a neglected tropical disease (NTD) that results from the injection of snake venom of a venomous snake into animals and humans. In Africa (mainly in sub-Saharan Africa), over 100,000 envenomings and over 10,000 deaths per annum from snakebite have been reported. Difficulties in snakebite prevention and antivenom treatment are believed to result from a lack of epidemiological data and underestimated figures on snakebite envenoming-related morbidity and mortality. There are species- and genus-specific variations associated with snake venoms in Africa and across the globe. These variations contribute massively to diverse differences in venom toxicity and pathogenicity that can undermine the efficacy of adopted antivenom therapies used in the treatment of snakebite envenoming. There is a need to profile all snake venom proteins of medically important venomous snakes endemic to Africa. This is anticipated to help in the development of safer and more effective antivenoms for the treatment of snakebite envenoming within the continent. In this review, the proteomes of 34 snake venoms from the most medically important snakes in Africa, namely the Viperidae and Elipdae, were extracted from the literature. The toxin families were grouped into dominant, secondary, minor, and others based on the abundance of the protein families in the venom proteomes. The Viperidae venom proteome was dominated by snake venom metalloproteinases (SVMPs-41%), snake venom serine proteases (SVSPs-16%), and phospholipase A2 (PLA2-17%) protein families, while three-finger toxins (3FTxs-66%) and PLA2s (16%) dominated those of the Elapidae. We further review the neutralisation of these snake venoms by selected antivenoms widely used within the African continent. The profiling of African snake venom proteomes will aid in the development of effective antivenom against snakebite envenoming and, additionally, could possibly reveal therapeutic applications of snake venom proteins.

Divergent Specialization of Simple Venom Gene Profiles among Rear-Fanged Snake Genera (Helicops and Leptodeira, Dipsadinae, Colubridae)

Many venomous animals express toxins that show extraordinary levels of variation both within and among species. In snakes, most studies of venom variation focus on front-fanged species in the families Viperidae and Elapidae, even though rear-fanged snakes in other families vary along the same ecological axes important to venom evolution. Here we characterized venom gland transcriptomes from 19 snakes across two dipsadine rear-fanged genera (Leptodeira and Helicops, Colubridae) and two front-fanged genera (Bothrops, Viperidae; Micrurus, Elapidae). We compared patterns of composition, variation, and diversity in venom transcripts within and among all four genera. Venom gland transcriptomes of rear-fanged Helicops and Leptodeira and front-fanged Micrurus are each dominated by expression of single toxin families (C-type lectins, snake venom metalloproteinase, and phospholipase A2, respectively), unlike highly diverse front-fanged Bothrops venoms. In addition, expression patterns of congeners are much more similar to each other than they are to species from other genera. These results illustrate the repeatability of simple venom profiles in rear-fanged snakes and the potential for relatively constrained venom composition within genera.

Profilings of subproteomes of lectin-binding proteins of nine Bothrops venoms reveal variability driven by different glycan types

Snake venom proteomes have long been investigated to explore a multitude of biologically active components that are used for prey capture and defense, and are involved in the pathological effects observed upon mammalian envenomation. Glycosylation is a major protein post-translational modification in venoms and contributes to the diversification of proteomes. We have shown that Bothrops venoms are markedly defined by their content of glycoproteins, and that most N-glycan structures of eight Bothrops venoms contain sialic acid, while bisected N-acetylglucosamine was identified in Bothrops cotiara venom. To further investigate the mechanisms involved in the generation of different venoms by related snakes, here the glycoproteomes of nine Bothrops venoms (Bothrops atrox, B. cotiara, Bothrops erythromelas, Bothrops fonsecai, B. insularis, Bothrops jararaca, Bothrops jararacussu, Bothrops moojeni and Bothrops neuwiedi) were comparatively analyzed by enrichment with three lectins of different specificities, recognizing bisecting N-acetylglucosamine- and sialic acid-containing glycoproteins, and mass spectrometry. The lectin capture strategy generated venom fractions enriched with several glycoproteins, including metalloprotease, serine protease, and L- amino acid oxidase, in addition to various types of low abundant enzymes. The different contents of lectin-enriched proteins underscore novel aspects of the variability of the glycoprotein subproteomes of Bothrops venoms and point to the role of distinct types of glycan chains in generating different venoms by closely related snake species.

Evidence that BJcuL, a C-type lectin from Bothrops jararacussu venom, influences deubiquitinase activity, resulting in the accumulation of anti-apoptotic proteins in two colorectal cancer cell lines

BJcuL is a snake venom C-type lectin (SVCTL) purified from the snake's venom Bothrops jararacussu. It has been previously demonstrated that BJcuL induces the accumulation of pro-apoptotic proteins of the extrinsic pathway, such as FADD and caspase-8, in the colorectal cancer cell line HT29, suggesting that the lectin may be able to enhance TRAIL-induced apoptosis. To test this hypothesis, we exposed two colorectal cancer cell lines, HT29 and HCT116, to increasing concentrations of BJcuL (1-20 μg/mL) in the presence or absence of TRAIL. Contrary to our expectations, however, BJcuL was unable to induce apoptosis in these cells, as shown by annexin-V/7AAD, clonogenic assays, and immunoblotting. Nevertheless, BJcuL was able to induce the accumulation of FADD and caspase-8, as well as anti-apoptotic proteins such as c-FLIP and survivin and poly-ubiquitinated proteins. Incubation with the deubiquitinase inhibitor WP1130 (10 μM) resulted in decreased BJcuL-induced survivin levels. Altogether, our results evince the effects of SVCTL on the ubiquitin-proteasome system in vitro for the first time. Compounds that can influence such system are important tools in the search for new therapeutic or diagnostic targets in cancer since they can elucidate the molecular mechanisms involved in determining cell fate as well as contributing to drug-development strategies in partnership with the pharmaceutical industry.

Interpopulational variation and ontogenetic shift in the venom composition of Lataste's viper (Vipera latastei, Boscá 1878) from northern Portugal

Lataste's viper (Vipera latastei) is a venomous European viper endemic to the Iberian Peninsula, recognised as medically important by the World Health Organization. To date, no comprehensive characterisation of this species' venom has been reported. Here, we analysed the venoms of juvenile and adult specimens of V. latastei from two environmentally different populations from northern Portugal. Using bottom-up venomics, we produced six venom proteomes (three per population) from vipers belonging to both age classes (i.e., two juveniles and four adults), and RP-HPLC profiles of 54 venoms collected from wild specimens. Venoms from juveniles and adults differed in their chromatographic profiles and relative abundances of their toxins, suggesting the occurrence of ontogenetic changes in venom composition. Specifically, snake venom metalloproteinase (SVMP) was the most abundant toxin family in juvenile venoms, while snake venom serine proteinases (SVSPs), phospholipases A₂ (PLA₂s), and C-type lectin-like (CTLs) proteins were the main toxins comprising adult venoms. The RP-HPLC venom profiles were found to vary significantly between the two sampled localities, indicating geographic variability. Furthermore, the presence/absence of certain peaks in the venom chromatographic profiles appeared to be significantly correlated also to factors like body size and sex of the vipers. Our findings show that V. latastei venom is a variable phenotype. The intraspecific differences we detected in its composition likely mirror changes in the feeding ecology of this species, taking place during different life stages and under different environmental pressures. SIGNIFICANCE: Lataste's viper (Vipera latastei) is a medically important viper endemic to the Iberian Peninsula, inhabiting different habitats and undergoing a marked ontogenetic dietary shift. In the current study, we report the first proteomic analysis of V. latastei venom from two environmentally different localities in northern Portugal. Our bottom-up venomic analyses show that snake venom serine proteinases (SVSPs), phospholipases A2 (PLA2s), and C-type lectin-like (CTLs) proteins are the major components of adult V. latastei venom. The comparative analysis of young and adult venoms suggests the occurrence of ontogenetic shift in toxin abundances, with snake venom metalloproteinases (SVMPs) being the predominant toxins in juvenile venoms. Moreover, geographic venom variation between the two studied populations is also detected, with our statistical analyses suggesting that factors like body size and sex of the vipers are possibly at play in its determination. Our work represents the first assessment of the composition of V. latastei venom, and the first step towards a better understanding of the drivers behind its variability.

Viper venoms drive the macrophages and hepatocytes to sequester and clear platelets: novel mechanism and therapeutic strategy for venom-induced thrombocytopenia

Venomous snakebites cause clinical manifestations that range from local to systemic and are considered a significant global health challenge. Persistent or refractory thrombocytopenia has been frequently reported in snakebite patients, especially in cases caused by viperidae snakes. Viper envenomation-induced thrombocytopenia may persist in the absence of significant consumption coagulopathy even after the antivenom treatment, yet the mechanism remains largely unknown. Our study aims to investigate the mechanism and discover novel therapeutic targets for coagulopathy-independent thrombocytopenia caused by viper envenomation. Here we found that patients bitten by Protobothrops mucrosquamatus and Trimeresurus stejnegeri, rather than Naja. atra may develop antivenom-resistant and coagulopathy-independent thrombocytopenia. Crude venoms and the derived C-type lectin-like proteins from these vipers significantly increased platelet surface expression of neuraminidase and platelet desialylation, therefore led to platelet ingestion by both macrophages and hepatocytes in vitro, and drastically decreased peripheral platelet counts in vivo. Our study is the first to demonstrate that desialylation-mediated platelet clearance is a novel mechanism of viper envenomation-induced refractory thrombocytopenia and C-type lectin-like proteins derived from the viper venoms contribute to snake venom-induced thrombocytopenia. The results of this study suggest the inhibition of platelet desialylation as a novel therapeutic strategy against viper venom-induced refractory thrombocytopenia.

Exploring the five-paced viper (Deinagkistrodon acutus) venom proteome by integrating a combinatorial peptide ligand library approach with shotgun LC-MS/MS

BACKGROUND

Snake venoms are complex mixtures of toxic proteins or peptides encoded by various gene families that function synergistically to incapacitate prey. In the present study, in order to unravel the proteomic repertoire of Deinagkistrodon acutus venom, some trace abundance components were analyzed.

METHODS

Shotgun proteomic approach combined with shotgun nano-LC-ESI-MS/MS were employed to characterize the medically important D. acutus venom, after collected samples were enriched with the combinatorial peptide ligand library (CPLL).

RESULTS

This avenue helped us find some trace components, undetected before, in D. acutus venom. The results indicated that D. acutus venom comprised 84 distinct proteins from 10 toxin families and 12 other proteins. These results are more than twice the number of venom components obtained from previous studies, which were only 29 distinct proteins obtained through RP-HPLC for the venom of the same species. The present results indicated that in D. acutus venom, the most abundant components (66.9%) included metalloproteinases, serine proteinases, and C-type lectin proteins; the medium abundant components (13%) comprised phospholipases A2 (PLA2) and 5'-nucleotidases and nucleases; whereas least abundant components (6%) were aminopeptidases, L-amino acid oxidases (LAAO), neurotoxins and disintegrins; and the trace components. The last were undetected before the use of conventional shotgun proteomics combined with shotgun nano-LC-ESI-MS/MS, such as cysteine-rich secretory proteins Da-CRPa, phospholipases B-like 1, phospholipases B (PLB), nerve growth factors (NGF), glutaminyl-peptide cyclortransferases (QC), and vascular non-inflammatory molecules 2 (VNN2).

CONCLUSION

These findings demonstrated that the CPLL enrichment method worked well in finding the trace toxin proteins in D. acutus venom, in contrast with the previous venomic characterization of D. acutus by conventional LC-MS/MS. In conclusion, this approach combined with the CPLL enrichment was effective for allowing us to explore the hidden D. acutus venomic profile and extended the list of potential venom toxins.

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

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

Targeted identification of C-type lectins in snake venom by 2DE and Western blot

C-type lectins (CTL) and CTL-like proteins (snaclecs) are important toxins found in snake venom which can disrupt hemostasis by binding platelet membrane glycoproteins. Traditional identification of these toxins usually relies on an "activity-directed fractionation" approach which is very arduous. Here, we report a new method for rapid screening of these proteins in snake venom.

METHODS

A conserved and immunogenic peptide found in svCTLs (CTL and snaclecs) was identified by sequence alignment using DNAStar software. The peptide was de novo synthesized and conjugated to keyhole limpet hemocyanin (KLH). Rabbit antibodies were generated against the peptide by classical immunization. Deinagkistrodon acutus venom was separated by two-dimensional electrophoresis (2DE) followed by Western blot and CTLs immunodetected using the isolated polyclonal antibody. The same svCTL spots on a parallel 2DE gel were isolated and analyzed by MALDI-TOF-MS.

RESULTS

A highly conserved peptide with the sequence "KTWDDAEKFCTEQ" was identified as a common epitope in svCTLs. The polyclonal antibody against the 13aa-peptide was successfully prepared and purified. Its usefulness to detect svCTLs in D. acutus venom was tested by 2DE-WB and we determined that it positively identified all known D. acutus venom CTLs.

CONCLUSIONS

Immunodetection with antibodies against KTWDDAEKFCTEQ is an efficient strategy to identify novel svCTLs in the context of a complex proteome.

Snake Venom Gland Organoids

Wnt dependency and Lgr5 expression define multiple mammalian epithelial stem cell types. Under defined growth factor conditions, such adult stem cells (ASCs) grow as 3D organoids that recapitulate essential features of the pertinent epithelium. Here, we establish long-term expanding venom gland organoids from several snake species. The newly assembled transcriptome of the Cape coral snake reveals that organoids express high levels of toxin transcripts. Single-cell RNA sequencing of both organoids and primary tissue identifies distinct venom-expressing cell types as well as proliferative cells expressing homologs of known mammalian stem cell markers. A hard-wired regional heterogeneity in the expression of individual venom components is maintained in organoid cultures. Harvested venom peptides reflect crude venom composition and display biological activity. This study extends organoid technology to reptilian tissues and describes an experimentally tractable model system representing the snake venom gland.

Toxinology provides multidirectional and multidimensional opportunities: A personal perspective

In nature, toxins have evolved as weapons to capture and subdue the prey or to counter predators or competitors. When they are inadvertently injected into humans, they cause symptoms ranging from mild discomfort to debilitation and death. Toxinology is the science of studying venoms and toxins that are produced by a wide variety of organisms. In the past, the structure, function and mechanisms of most abundant and/or most toxic components were characterized to understand and to develop strategies to neutralize their toxicity. With recent technical advances, we are able to evaluate and determine the toxin profiles using transcriptomes of venom glands and proteomes of tiny amounts of venom. Enormous amounts of data from these studies have opened tremendous opportunities in many directions of basic and applied research. The lower costs for profiling venoms will further fuel the expansion of toxin database, which in turn will provide greater exciting and bright opportunities in toxin research.

Chronic oral safety study of the aqueous extract of Combretum molle twigs on biochemical, haematological and antioxidant parameters of Wistar rats

BACKGROUND

Combretum molle R.B/G. Don (Combretaceae) is a graceful deciduous shrub, distributed especially in tropical Africa and used in traditional medicine in the treatment of malaria, diabetes, and bacterial, liver and cardiovascular deseases. To our knowledge, no long-term toxicity studies of C. molle has ever been realized yet.

METHODS

The long-term toxicity study was conducted in accordance with OECD 408 guidelines with slight modifications. In fact, rats were divided in groups and treated orally with CMAE at doses of 62.5, 125 and 250 mg/kg for 6 months. The general behavior and signs of toxicity of the rats were daily observed. Body weight, food and water intake were recorded every 2 months for 6 months. At the end of treatment period, urine and blood samples were collected for hematological, biochemical and antioxidant estimations. Immediately, internal organs were collected and weighed.

RESULTS

The results showed that no mortality and visible signs of the toxicity were recorded in all experimental animals. The administration of CMAE had no significant effects on body weight, organ weights, serum electrolyte, and food and water intake. However, all doses of CMAE produced an increase in high density lipoprotein cholesterol, white blood cells, platelets, glutathione, and a decrease in low density lipoprotein cholesterol and malondialdehyde rate. CMAE at doses of 125 and 250 mg/kg decreased in serum proteins and the activity of aspartate amino transferase, and increased the activity of catalase. In addition, CMAE (250 mg/kg) significantly decreased the alanine aminotransferase activity and the level of triglycerides, very low density cholesterol, total proteins and creatinine, and increased in renal clearance, red blood cells, hemoglobin, hematocrit and superoxide dismutase activity.

CONCLUSIONS

At the end of this study, no signs of major intoxication was noted during 6 months of treatment. These results suggest that long-term consumption of CMAE at the therapeutic dose (250 mg/kg) presents low risks to human health.

High throughput screening and identification of coagulopathic snake venom proteins and peptides using nanofractionation and proteomics approaches

Snakebite is a neglected tropical disease that results in a variety of systemic and local pathologies in envenomed victims and is responsible for around 138,000 deaths every year. Many snake venoms cause severe coagulopathy that makes victims vulnerable to suffering life-threating haemorrhage. The mechanisms of action of coagulopathic snake venom toxins are diverse and can result in both anticoagulant and procoagulant effects. However, because snake venoms consist of a mixture of numerous protein and peptide components, high throughput characterizations of specific target bioactives is challenging. In this study, we applied a combination of analytical and pharmacological methods to identify snake venom toxins from a wide diversity of snake species that perturb coagulation. To do so, we used a high-throughput screening approach consisting of a miniaturised plasma coagulation assay in combination with a venom nanofractionation approach. Twenty snake venoms were first separated using reversed-phase liquid chromatography, and a post-column split allowed a small fraction to be analyzed with mass spectrometry, while the larger fraction was collected and dispensed onto 384-well plates. After fraction collection, any solvent present in the wells was removed by means of freeze-drying, after which it was possible to perform a plasma coagulation assay in order to detect coagulopathic activity. Our results demonstrate that many snake venoms simultaneously contain both procoagulant and anticoagulant bioactives that contribute to coagulopathy. In-depth identification analysis from seven medically-important venoms, via mass spectrometry and nanoLC-MS/MS, revealed that phospholipase A2 toxins are frequently identified in anticoagulant venom fractions, while serine protease and metalloproteinase toxins are often associated with procoagulant bioactivities. The nanofractionation and proteomics approach applied herein seems likely to be a valuable tool for the rational development of next-generation snakebite treatments by facilitating the rapid identification and fractionation of coagulopathic toxins, thereby enabling specific targeting of these toxins by new therapeutics such as monoclonal antibodies and small molecule inhibitors.

Venomics of the asp viper Vipera aspis aspis from France

The asp viper Vipera aspis aspis is a venomous snake found in France, and despite its medical importance, the complete toxin repertoire produced is unknown. Here, we used a venomics approach to decipher the composition of its venom. Transcriptomic analysis revealed 80 venom-annotated sequences grouped into 16 gene families. Among the most represented toxins were snake venom metalloproteases (23%), phospholipases A2 (15%), serine proteases (13%), snake venom metalloprotease inhibitors (13%) and C-type lectins (12%). LC-MS of venoms revealed similar profiles regardless of the method of extraction (milking vs defensive bite). Proteomic analysis validated 57 venom-annotated transcriptomic sequences (>70%), including one for each of the 16 families, but also identified 7 sequences not initially annotated as venom proteins, including a serine protease, a disintegrin, a glutaminyl-peptide cyclotransferase, a proactivator polypeptide-like and 3 aminopeptidases. Interestingly, phospholipases A2 were the dominant proteins in the venom, among which included an ammodytoxin B-like sequence, which may explain the reported neurotoxicity following some asp viper envenomations. In total, 87 sequences were retrieved from the Vipera aspis aspis transcriptome and proteome, constituting a valuable resource that will help in understanding the toxinological basis of clinical signs of envenoming and for the mining of useful pharmacological compounds. BIOLOGICAL SIGNIFICANCE: The asp viper (Vipera aspis aspis) causes several hundred envenomations annually in France, including unusual cases with neurological signs, resulting in one death per year on average. Here, we performed a proteotranscriptomic analysis of V. a. aspis venom in order to provide a better understanding of its venom composition. We found that, as in other Vipera species, phospholipase A2 dominates in the venom, and the presence of a sequence related to ammodytoxin B may explain the reported neurotoxicity following some asp viper envenomations. Thus, this study will help in informing the toxinological basis of clinical signs of envenoming.

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.

The Sequence and a Three-Dimensional Structural Analysis Reveal Substrate Specificity Among Snake Venom Phosphodiesterases

(1) Background. Snake venom phosphodiesterases (SVPDEs) are among the least studied venom enzymes. In envenomation, they display various pathological effects, including induction of hypotension, inhibition of platelet aggregation, edema, and paralysis. Until now, there have been no 3D structural studies of these enzymes, thereby preventing structure-function analysis. To enable such investigations, the present work describes the model-based structural and functional characterization of a phosphodiesterase from Crotalusadamanteus venom, named PDE_Ca. (2) Methods. The PDE_Ca structure model was produced and validated using various software (model building: I-TESSER, MODELLER 9v19, Swiss-Model, and validation tools: PROCHECK, ERRAT, Molecular Dynamic Simulation, and Verif3D). (3) Results. The proposed model of the enzyme indicates that the 3D structure of PDE_Ca comprises four domains, a somatomedin B domain, a somatomedin B-like domain, an ectonucleotide pyrophosphatase domain, and a DNA/RNA non-specific domain. Sequence and structural analyses suggest that differences in length and composition among homologous snake venom sequences may account for their differences in substrate specificity. Other properties that may influence substrate specificity are the average volume and depth of the active site cavity. (4) Conclusion. Sequence comparisons indicate that SVPDEs exhibit high sequence identity but comparatively low identity with mammalian and bacterial PDEs.

Identification of a α-helical molten globule intermediate and structural characterization of β-cardiotoxin, an all β-sheet protein isolated from the venom of Ophiophagus hannah (king cobra)

β-Cardiotoxin is a novel member of the snake venom three-finger toxin (3FTX) family. This is the first exogenous protein to antagonize β-adrenergic receptors and thereby causing reduction in heart rates (bradycardia) when administered into animals, unlike the conventional cardiotoxins as reported earlier. 3FTXs are stable all β-sheet peptides with 60-80 amino acid residues. Here, we describe the three-dimensional crystal structure of β-cardiotoxin together with the identification of a molten globule intermediate in the unfolding pathway of this protein. In spite of the overall structural similarity of this protein with conventional cardiotoxins, there are notable differences observed at the loop region and in the charge distribution on the surface, which are known to be critical for cytolytic activity of cardiotoxins. The molten globule intermediate state present in the thermal unfolding pathway of β-cardiotoxin was however not observed during the chemical denaturation of the protein. Interestingly, circular dichroism (CD) and NMR studies revealed the presence of α-helical secondary structure in the molten globule intermediate. These results point to substantial conformational plasticity of β-cardiotoxin, which might aid the protein in responding to the sometimes conflicting demands of structure, stability, and function during its biological lifetime.

Structurally Robust and Functionally Highly Versatile-C-Type Lectin (-Related) Proteins in Snake Venoms

Snake venoms contain an astounding variety of different proteins. Among them are numerous C-type lectin family members, which are grouped into classical Ca²⁺- and sugar-binding lectins and the non-sugar-binding snake venom C-type lectin-related proteins (SV-CLRPs), also called snaclecs. Both groups share the robust C-type lectin domain (CTLD) fold but differ in a long loop, which either contributes to a sugar-binding site or is expanded into a loop-swapping heterodimerization domain between two CLRP subunits. Most C-type lectin (-related) proteins assemble in ordered supramolecular complexes with a high versatility of subunit numbers and geometric arrays. Similarly versatile is their ability to inhibit or block their target molecules as well as to agonistically stimulate or antagonistically blunt a cellular reaction triggered by their target receptor. By utilizing distinct interaction sites differentially, SV-CLRPs target a plethora of molecules, such as distinct coagulation factors and receptors of platelets and endothelial cells that are involved in hemostasis, thrombus formation, inflammation and hematogenous metastasis. Because of their robust structure and their high affinity towards their clinically relevant targets, SV-CLRPs are and will potentially be valuable prototypes to develop new diagnostic and therapeutic tools in medicine, provided that the molecular mechanisms underlying their versatility are disclosed.

Exposure to Aeromonas hydrophila induces inflammation and increases expression of the gene encoding for a putative dual CTLD-containing lectin in milkfish liver

Milkfish (Chanos chanos Forsskal) is an important aquaculture product and is the sole extant species of the family Chanidae (order Gonorynchiformes). While there are already several reports regarding milkfish aquaculture, studies on milkfish immunity and gene expression are very limited. In this study, we showed that Aeromonas hydrophila induces inflammation in milkfish liver. We identified a milkfish C-type lectin-like domain containing proteins (CTLDcps) gene, designated as CcClec, which was upregulated in respond to A. hydrophila. Full-length sequencing was performed using Rapid Amplification of cDNA Ends (RACE PCR) to produce a complete Coding DNA Sequence (CDS) of the gene. The CcClec gene encoded a predicted protein of 340 amino acids containing two CTLDs that may potentially bind carbohydrates, especially sucrose and cellobiose. The CcClec mRNA transcript was expressed highest in the liver, followed by head kidney, brain, heart, gills, spleen, and midgut. CcClec transcripts were upregulated in damaged liver upon exposure to A. hydrophila. Overall, these findings demonstrated that CcClec is implicated in milkfish innate immunity, and is most highly expressed in the liver, suggesting a role of the liver in the milkfish immune system.

Snake Venoms in Cancer Therapy: Past, Present and Future

Cancer is one of the leading causes of morbidity and mortality worldwide, and the discovery of new drugs for cancer therapy is one of the most important objectives for the pharmaceutical industry. Snake venoms are complex mixtures containing different peptides, proteins, enzymes, carbohydrates and other bioactive molecules, which are secreted by the snake in the predation or defending against threats. Understanding the snake venoms may turn the toxins into a valuable source of new lead compounds in drug discovery. Captopril, the first angiotensin-converting enzyme inhibitor approved in 1981 by FDA, was designed based on the structure of a peptide isolated from the snake venom. The earliest reports about snake venoms used in cancer treatments appeared in the 1930s. Since then, numerous studies on the activities, isolations, purifications and structure elucidations of the components from snake venoms were published. The comprehensive structural and functional investigations of snake venoms would contribute to the development of novel anti-cancer drugs. Our review will focus on the past, present and the future of the studies on snake venoms in cancer target therapy.

Comprehensive Snake Venomics of the Okinawa Habu Pit Viper, Protobothrops flavoviridis, by Complementary Mass Spectrometry-Guided Approaches

The Asian world is home to a multitude of venomous and dangerous snakes, which are used to induce various medical effects in the preparation of traditional snake tinctures and alcoholics, like the Japanese snake wine, named Habushu. The aim of this work was to perform the first quantitative proteomic analysis of the Protobothrops flavoviridis pit viper venom. Accordingly, the venom was analyzed by complimentary bottom-up and top-down mass spectrometry techniques. The mass spectrometry-based snake venomics approach revealed that more than half of the venom is composed of different phospholipases A2 (PLA₂). The combination of this approach and an intact mass profiling led to the identification of the three main Habu PLA₂s. Furthermore, nearly one-third of the total venom consists of snake venom metalloproteinases and disintegrins, and several minor represented toxin families were detected: C-type lectin-like proteins (CTL), cysteine-rich secretory proteins (CRISP), snake venom serine proteases (svSP), l-amino acid oxidases (LAAO), phosphodiesterase (PDE) and 5'-nucleotidase. Finally, the venom of P. flavoviridis contains certain bradykinin-potentiating peptides and related peptides, like the svMP inhibitors, pEKW, pEQW, pEEW and pENW. In preliminary MTT cytotoxicity assays, the highest cancerous-cytotoxicity of crude venom was measured against human neuroblastoma SH-SY5Y cells and shows disintegrin-like effects in some fractions.

The habu genome reveals accelerated evolution of venom protein genes

Evolution of novel traits is a challenging subject in biological research. Several snake lineages developed elaborate venom systems to deliver complex protein mixtures for prey capture. To understand mechanisms involved in snake venom evolution, we decoded here the ~1.4-Gb genome of a habu, Protobothrops flavoviridis. We identified 60 snake venom protein genes (SV) and 224 non-venom paralogs (NV), belonging to 18 gene families. Molecular phylogeny reveals early divergence of SV and NV genes, suggesting that one of the four copies generated through two rounds of whole-genome duplication was modified for use as a toxin. Among them, both SV and NV genes in four major components were extensively duplicated after their diversification, but accelerated evolution is evident exclusively in the SV genes. Both venom-related SV and NV genes are significantly enriched in microchromosomes. The present study thus provides a genetic background for evolution of snake venom composition.

Orphan Three-Finger Toxins Bind at Tissue Factor-Factor VIIa Interface to Inhibit Factor X Activation: Identification of Functional Site by Docking

Three-finger toxins (3FTxs) contribute to toxicity of venomous snakes belonging to the family Elapidae. Currently, functions of a considerable proportion of 3FTxs are still unknown. Here, we describe the function of orphan group I 3FTxs consisting of four members. We also identified a new member of this group by sequencing a transcript isolated from Naja naja venom. This transcript, named najalexin, is identical to that previously described 3FTx from Naja atra venom gland, and shared high sequence identity with ringhalexin from Hemachatus haemachatus and a hypothetical protein from Ophiophagus hannah (here named as ophiolexin). The three-dimensional structure, as predicted by molecular modeling, showed that najalexin and ophiolexin share the same conserved structural organization as ringhalexin and other 3FTxs. Since ringhalexin inhibits the activation of factor X by the tissue factor-factor VIIa complex (TF-FVIIa), we evaluated the interaction of this group of 3FTxs with all components using in silico protein-protein docking studies. The binding of orphan group I 3FTxs to TF-FVIIa complex appears to be driven by their interaction with TF. They bind to fibronectin domain closer to the 170-loop of the FVIIa heavy chain to inhibit factor X activation. The docking studies reveal that functional site residues Tyr7, Lys9, Glu12, Lys26, Arg34, Leu35, Arg40, Val55, Asp56, Cys57, Cys58, and Arg65 on these 3FTxs are crucial for interaction. In silico replacement of these residues by Ala resulted in significant effects in the binding energies. Furthermore, these functional residues are not found in other groups of 3FTxs, which exhibit distinct pharmacological properties.

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.

Pharmacokinetics of Snake Venom

Understanding snake venom pharmacokinetics is essential for developing risk assessment strategies and determining the optimal dose and timing of antivenom required to bind all venom in snakebite patients. This review aims to explore the current knowledge of snake venom pharmacokinetics in animals and humans. Literature searches were conducted using EMBASE (1974–present) and Medline (1946–present). For animals, 12 out of 520 initially identified studies met the inclusion criteria. In general, the disposition of snake venom was described by a two-compartment model consisting of a rapid distribution phase and a slow elimination phase, with half-lives of 5 to 48 min and 0.8 to 28 h, respectively, following rapid intravenous injection of the venoms or toxins. When the venoms or toxins were administered intramuscularly or subcutaneously, an initial absorption phase and slow elimination phase were observed. The bioavailability of venoms or toxins ranged from 4 to 81.5% following intramuscular administration and 60% following subcutaneous administration. The volume of distribution and the clearance varied between snake species. For humans, 24 out of 666 initially identified publications contained sufficient information and timed venom concentrations in the absence of antivenom therapy for data extraction. The data were extracted and modelled in NONMEM. A one-compartment model provided the best fit, with an elimination half-life of 9.71 ± 1.29 h. It is intended that the quantitative information provided in this review will provide a useful basis for future studies that address the pharmacokinetics of snakebite in humans.

Revisiting the Therapeutic Potential of Bothrops jararaca Venom: Screening for Novel Activities Using Connectivity Mapping

Snake venoms are sources of molecules with proven and potential therapeutic applications. However, most activities assayed in venoms (or their components) are of hemorrhagic, hypotensive, edematogenic, neurotoxic or myotoxic natures. Thus, other relevant activities might remain unknown. Using functional genomics coupled to the connectivity map (C-map) approach, we undertook a wide range indirect search for biological activities within the venom of the South American pit viper Bothrops jararaca. For that effect, venom was incubated with human breast adenocarcinoma cell line (MCF7) followed by RNA extraction and gene expression analysis. A list of 90 differentially expressed genes was submitted to biosimilar drug discovery based on pattern recognition. Among the 100 highest-ranked positively correlated drugs, only the antihypertensive, antimicrobial (both antibiotic and antiparasitic), and antitumor classes had been previously reported for B. jararaca venom. The majority of drug classes identified were related to (1) antimicrobial activity; (2) treatment of neuropsychiatric illnesses (Parkinson’s disease, schizophrenia, depression, and epilepsy); (3) treatment of cardiovascular diseases, and (4) anti-inflammatory action. The C-map results also indicated that B. jararaca venom may have components that target G-protein-coupled receptors (muscarinic, serotonergic, histaminergic, dopaminergic, GABA, and adrenergic) and ion channels. Although validation experiments are still necessary, the C-map correlation to drugs with activities previously linked to snake venoms supports the efficacy of this strategy as a broad-spectrum approach for biological activity screening, and rekindles the snake venom-based search for new therapeutic agents.

Anticoagulation beyond direct thrombin and factor Xa inhibitors: indications for targeting the intrinsic pathway?

Antithrombotic drugs like vitamin K antagonists and heparin have been the gold standard for the treatment and prevention of thromboembolic disease for many years. Unfortunately, there are several disadvantages of these antithrombotic drugs: they are accompanied by serious bleeding problems, it is necessary to monitor the therapeutic window, and there are various interactions with food and other drugs. This has led to the development of new oral anticoagulants, specifically inhibiting either thrombin or factor Xa. In terms of effectiveness, these drugs are comparable to the currently available anticoagulants; however, they are still associated with issues such as bleeding, reversal of the drug and complicated laboratory monitoring. Vitamin K antagonists, heparin, direct thrombin and factor Xa inhibitors have in common that they target key proteins of the haemostatic system. In an attempt to overcome these difficulties we investigated whether the intrinsic coagulation factors (VIII, IX, XI, XII, prekallikrein and high-molecular-weight kininogen) are superior targets for anticoagulation. We analysed epidemiological data concerning thrombosis and bleeding in patients deficient in one of the intrinsic pathway proteins. Furthermore, we discuss several thrombotic models in intrinsic coagulation factor-deficient animals. The combined results suggest that intrinsic coagulation factors could be suitable targets for anticoagulant drugs.

Dramatic and concerted conformational changes enable rhodocetin to block α2β1 integrin selectively

The collagen binding integrin α2β1 plays a crucial role in hemostasis, fibrosis, and cancer progression amongst others. It is specifically inhibited by rhodocetin (RC), a C-type lectin-related protein (CLRP) found in Malayan pit viper (Calloselasma rhodostoma) venom. The structure of RC alone reveals a heterotetramer arranged as an αβ and γδ subunit in a cruciform shape. RC specifically binds to the collagen binding A-domain of the integrin α2 subunit, thereby blocking collagen-induced platelet aggregation. However, until now, the molecular basis for this interaction has remained unclear. Here, we present the molecular structure of the RCγδ-α2A complex solved to 3.0 Å resolution. Our findings show that RC undergoes a dramatic structural reorganization upon binding to α2β1 integrin. Besides the release of the nonbinding RCαβ tandem, the RCγ subunit interacts with loop 2 of the α2A domain as result of a dramatic conformational change. The RCδ subunit contacts the integrin α2A domain in the “closed” conformation through its helix C. Combined with epitope-mapped antibodies, conformationally locked α2A domain mutants, point mutations within the α2A loop 2, and chemical modifications of the purified toxin protein, this molecular structure of RCγδ-α2A complex explains the inhibitory mechanism and specificity of RC for α2β1 integrin.

In animals, collagen-mediated platelet aggregation is an essential component of the blood’s clotting response following vascular injury. A small group of snake venom toxins belonging to the C-type lectin protein family exert their harmful effects by directly targeting this pathway. Rhodocetin (RC) is a heterotetrameric protein found in the venom of the Malayan pit viper (C. rhodostoma). RC specifically binds α2β1 integrin, the key protein required for collagen-mediated platelet aggregation. In this study, we describe the interaction between RC and α2β1 integrin at atomic resolution. This study reveals that RC undergoes a massive structural reorganization upon α2β1 integrin binding, such that RC’s αβ subunit is released from its γδ subunit and a γδ-α2β1 integrin complex is formed. The inhibitory nature of this complex can be readily explained as RC binding along the top surface of the α2β1 integrin and directly above the collagen binding site. As a result, access of collagen to its binding site is blocked, thereby preventing collagen-mediated platelet aggregation.

The Molecular Basis of Toxins' Interactions with Intracellular Signaling via Discrete Portals

An understanding of the molecular mechanisms by which microbial, plant or animal-secreted toxins exert their action provides the most important element for assessment of human health risks and opens new insights into therapies addressing a plethora of pathologies, ranging from neurological disorders to cancer, using toxinomimetic agents. Recently, molecular and cellular biology dissecting tools have provided a wealth of information on the action of these diverse toxins, yet, an integrated framework to explain their selective toxicity is still lacking. In this review, specific examples of different toxins are emphasized to illustrate the fundamental mechanisms of toxicity at different biochemical, molecular and cellular- levels with particular consideration for the nervous system. The target of primary action has been highlighted and operationally classified into 13 sub-categories. Selected examples of toxins were assigned to each target category, denominated as portal, and the modulation of the different portal’s signaling was featured. The first portal encompasses the plasma membrane lipid domains, which give rise to pores when challenged for example with pardaxin, a fish toxin, or is subject to degradation when enzymes of lipid metabolism such as phospholipases A₂ (PLA₂) or phospholipase C (PLC) act upon it. Several major portals consist of ion channels, pumps, transporters and ligand gated ionotropic receptors which many toxins act on, disturbing the intracellular ion homeostasis. Another group of portals consists of G-protein-coupled and tyrosine kinase receptors that, upon interaction with discrete toxins, alter second messengers towards pathological levels. Lastly, subcellular organelles such as mitochondria, nucleus, protein- and RNA-synthesis machineries, cytoskeletal networks and exocytic vesicles are also portals targeted and deregulated by other diverse group of toxins. A fundamental concept can be drawn from these seemingly different toxins with respect to the site of action and the secondary messengers and signaling cascades they trigger in the host. While the interaction with the initial portal is largely determined by the chemical nature of the toxin, once inside the cell, several ubiquitous second messengers and protein kinases/ phosphatases pathways are impaired, to attain toxicity. Therefore, toxins represent one of the most promising natural molecules for developing novel therapeutics that selectively target the major cellular portals involved in human physiology and diseases.

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.

Antiadhesive and cytotoxic effect of Iranian Vipera lebetina snake venom on lung epithelial cancer cells

Background:

Cancer is one of the major health problems worldwide. Hence, finding potent therapeutics from natural sources seems necessary. Snake venom of Vipera lebetina contains potential component with anticancer activities such as antiproliferation, migration, invasion, adhesion, and angiogenesis effect. Evaluation of cytotoxic and antiadhesive effect of V. lebetina venom on lung epithelial cancer tumor cell (TC-1) was the main aim of this study.

Materials and Methods:

Here, we purified snake venom of V. lebetina by fast protein liquid chromatography (FPLC) using Sephacryl S-200 hr column. The fractions collected and evaluated by SDS-PAGE analysis. The cytotoxicity and antiadhesive effect of crude venom and fractions on TC-1 cells were demonstrated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and adhesion assay, respectively.

Results:

Our results showed six fractions in FPLC diagram. V. lebetina crude venom and fractions showed dose-dependent cytotoxic effect on TC-1 cells. Fractions 2 and 5 showed high cytotoxic effect with high IC50 value (IC50 = 6 μg/ml for fraction 2 and IC50 = 7.3 μg/ml for fraction 5). Fractions 2 and 5 selected for analysis antiadhesive effect on TC-1 cells. Furthermore, our results showed that both fractions 2 and 5 had antiadhesive effect on TC-1 cells.

Conclusion:

Because of potent cytotoxic and antiadhesive effect of V. lebetina fractions on lung epithelial cancer cell line, it could be promising tools for further analysis as anticancer therapeutic development.

Proteomic Characterization and Comparison of Malaysian Tropidolaemus wagleri and Cryptelytrops purpureomaculatus Venom Using Shotgun-Proteomics

Tropidolaemus wagleri and Cryptelytrops purpureomaculatus are venomous pit viper species commonly found in Malaysia. Tandem mass spectrometry analysis of the crude venoms has detected different proteins in T. wagleri and C. purpureomaculatus. They were classified into 13 venom protein families consisting of enzymatic and nonenzymatic proteins. Enzymatic families detected in T. wagleri and C. purpureomaculatus venom were snake venom metalloproteinase, phospholipase A₂, l-amino acid oxidase, serine proteases, 5′-nucleotidase, phosphodiesterase, and phospholipase B. In addition, glutaminyl cyclotransferase was detected in C. purpureomaculatus. C-type lectin-like proteins were common nonenzymatic components in both species. Waglerin was present and unique to T. wagleri—it was not in C. purpureomaculatus venom. In contrast, cysteine-rich secretory protein, bradykinin-potentiating peptide, and C-type natriuretic peptide were present in C. purpureomaculatus venom. Composition of the venom proteome of T. wagleri and C. purpureomaculatus provides useful information to guide production of effective antivenom and identification of proteins with potential therapeutic applications.

Crystal structures of the ligand-binding region of uPARAP: effect of calcium ion binding

The proteins of the mannose receptor (MR) family share a common domain organization and have a broad range of biological functions. Urokinase plasminogen activator receptor-associated protein (uPARAP) (or Endo180) is a member of this family and plays an important role in extracellular matrix remodelling through interaction with its ligands, including collagens and urokinase plasminogen activator receptor (uPAR). We report the crystal structures of the first four domains of uPARAP (also named the ligand-binding region, LBR) at pH 7.4 in Ca(2+)-bound and Ca(2+)-free forms. The first domain (cysteine-rich or CysR domain) folds into a new and unique conformation different from the β-trefoil fold of typical CysR domains. The so-called long loop regions (LLRs) of the C-type lectin-like domain (CTLD) 1 and 2 (the third and fourth domain) mediate the direct contacts between these domains. These LLRs undergo a Ca(2+)-dependent conformational change, and this is likely to be the key structural determinant affecting the overall conformation of uPARAP. Our results provide a molecular mechanism to support the structural flexibility of uPARAP, and shed light on the structural flexibility of other members of the MR family.

Ringhalexin from Hemachatus haemachatus: A novel inhibitor of extrinsic tenase complex

Anticoagulant therapy is used for the prevention and treatment of thromboembolic disorders. Blood coagulation is initiated by the interaction of factor VIIa (FVIIa) with membrane-bound tissue factor (TF) to form the extrinsic tenase complex which activates FX to FXa. Thus, it is an important target for the development of novel anticoagulants. Here, we report the isolation and characterization of a novel anticoagulant ringhalexin from the venom of Hemachatus haemachatus (African Ringhals Cobra). Amino acid sequence of the protein indicates that it belongs to the three-finger toxin family and exhibits 94% identity to an uncharacterized Neurotoxin-like protein NTL2 from Naja atra. Ringhalexin inhibited FX activation by extrinsic tenase complex with an IC50 of 123.8 ± 9.54 nM. It is a mixed-type inhibitor with the kinetic constants, Ki and Ki' of 84.25 ± 3.53 nM and 152.5 ± 11.32 nM, respectively. Ringhalexin also exhibits a weak, irreversible neurotoxicity on chick biventer cervicis muscle preparations. Subsequently, the three-dimensional structure of ringhalexin was determined at 2.95 Å resolution. This study for the first time reports the structure of an anticoagulant three-finger toxin. Thus, ringhalexin is a potent inhibitor of the FX activation by extrinsic tenase complex and a weak, irreversible neurotoxin.

Lebein, a snake venom disintegrin, suppresses human colon cancer cells proliferation and tumor-induced angiogenesis through cell cycle arrest, apoptosis induction and inhibition of VEGF expression

Lebein, is an heterodimeric disintegrin isolated from Macrovipera lebetina snake venom that was previously characterized as an inhibitor of ADP-induced platelet aggregation. In this study, we investigated the effect of Lebein on the p53-dependent growth of human colon adenocarcinoma cell lines. We found that Lebein significantly inhibited LS174 (p53wt), HCT116 (p53wt), and HT29 (p53mut) colon cancer cell viability by inducing cell cycle arrest through the modulation of expression levels of the tumor suppression factor p53, cell cycle regulating proteins cyclin D1, CDK2, CDK4, retinoblastoma (Rb), CDK1, and cyclin-dependent kinase inhibitors p21 and p27. Interestingly, Lebein-induced apoptosis of colon cancer cells was dependent on their p53 status. Thus, in LS174 cells, cell death was associated with PARP cleavage and the activation of caspases 3 and 8 while in HCT116 cells, Lebein induced caspase-independent apoptosis through increased expression of apoptosis inducing factor (AIF). In LS174 cells, Lebein triggers the activation of the MAPK ERK1/2 pathway through induction of reactive oxygen species (ROS). It also decreased cell adhesion and migration to fibronectin through down regulation of α5β1 integrin. Moreover, Lebein significantly reduced the expression of two angiogenesis stimulators, Vascular Endothelial Growth Factor (VEGF) and Neuropilin 1 (NRP1). It inhibited the VEGF-induced neovascularization process in the quail embryonic CAM system and blocked the development of human colon adenocarcinoma in nude mice. Overall, our work indicates that Lebein may be useful to design a new therapy against colon cancer. © 2016 Wiley Periodicals, Inc.