Processing of Snake Venom Metalloproteinases: Generation of Toxin Diversity and Enzyme Inactivation

Exploring snake venoms beyond the primary sequence: From proteoforms to protein-protein interactions

Snakebite envenomation has been a long-standing global issue that is difficult to treat, largely owing to the flawed nature of current immunoglobulin-based antivenom therapy and the complexity of snake venoms as sophisticated mixtures of bioactive proteins and peptides. Comprehensive characterisation of venom compositions is essential to better understanding snake venom toxicity and inform effective and rationally designed antivenoms. Additionally, a greater understanding of snake venom composition will likely unearth novel biologically active proteins and peptides that have promising therapeutic or biotechnological applications. While a bottom-up proteomic workflow has been the main approach for cataloguing snake venom compositions at the toxin family level, it is unable to capture snake venom heterogeneity in the form of protein isoforms and higher-order protein interactions that are important in driving venom toxicity but remain underexplored. This review aims to highlight the importance of understanding snake venom heterogeneity beyond the primary sequence, in the form of post-translational modifications that give rise to different proteoforms and the myriad of higher-order protein complexes in snake venoms. We focus on current top-down proteomic workflows to identify snake venom proteoforms and further discuss alternative or novel separation, instrumentation, and data processing strategies that may improve proteoform identification. The current higher-order structural characterisation techniques implemented for snake venom proteins are also discussed; we emphasise the need for complementary and higher resolution structural bioanalytical techniques such as mass spectrometry-based approaches, X-ray crystallography and cryogenic electron microscopy, to elucidate poorly characterised tertiary and quaternary protein structures. We envisage that the expansion of the snake venom characterisation "toolbox" with top-down proteomics and high-resolution protein structure determination techniques will be pivotal in advancing structural understanding of snake venoms towards the development of improved therapeutic and biotechnology applications.

Assessing Target Specificity of the Small Molecule Inhibitor MARIMASTAT to Snake Venom Toxins: A Novel Application of Thermal Proteome Profiling

New treatments that circumvent the pitfalls of traditional antivenom therapies are critical to address the problem of snakebite globally. Numerous snake venom toxin inhibitors have shown promising cross-species neutralization of medically significant venom toxins in vivo and in vitro. The development of high-throughput approaches for the screening of such inhibitors could accelerate their identification, testing, and implementation and thus holds exciting potential for improving the treatments and outcomes of snakebite envenomation worldwide. Energetics-based proteomic approaches, including thermal proteome profiling and proteome integral solubility alteration (PISA) assays, represent "deep proteomics" methods for high throughput, proteome-wide identification of drug targets and ligands. In the following study, we apply thermal proteome profiling and PISA methods to characterize the interactions between venom toxin proteoforms in Crotalus atrox (Western Diamondback Rattlesnake) and the snake venom metalloprotease (SVMP) inhibitor marimastat. We investigate its venom proteome-wide effects and characterize its interactions with specific SVMP proteoforms, as well as its potential targeting of non-SVMP venom toxin families. We also compare the performance of PISA thermal window and soluble supernatant with insoluble precipitate using two inhibitor concentrations, providing the first demonstration of the utility of a sensitive high-throughput PISA-based approach to assess the direct targets of small molecule inhibitors for snake venom.

Maggot Kinase and Natural Thrombolytic Proteins

Thrombolytic enzymes constitute a class of proteases with antithrombotic functions. Derived from natural products and abundant in nature, certain thrombolytic enzymes, such as urokinase, earthworm kinase, and streptokinase, have been widely used in the clinical treatment of vascular embolic diseases. Fly maggots, characterized by their easy growth and low cost, are a traditional Chinese medicine recorded in the Compendium of Materia Medica. These maggots can also be used as raw material for the extraction and preparation of thrombolytic enzymes (maggot kinase). In this review, we assembled global research reports on natural thrombolytic enzymes through a literature search and reviewed the functions and structures of natural thrombolytic enzymes to provide a reference for natural thrombophilic drug screening and development.

Evaluation of venom diversity and antivenom quality from the venom of long-term captive vs recently wild captured Pseudocerastes persicus snake: An In vitro and In vivo study

Snakebite envenomation is a life-threatening condition and antivenoms are used as the most effective treatment. Venom obtained from snakes in long-term captivity showed some variations in comparison to the venom of the wild snakes. The objective of this study is to compare the venom of the Pseudocerastes persicus under long-term captivity and wild conditions as well as the antivenom obtained from these venoms. We have analyzed venom samples and produced trivalent antivenoms using the venom of long-term captive (LTC) or recently wild-captured (RWC) Pseudocerastes persicus, and RWC Macrovipera lebetina, and Echis carinatus. The HPLC analysis revealed that the RWC snakes' venom had three peaks that were not present in the LTC snake's venom. Further analysis using MALDI-TOF and MS/MS showed that the fraction with a retention time (RT) of 14 min contained a toxin from the Kunitz-type serine protease inhibitor (KUT) class, while the fraction with RT 21 a peptide identified within the snake venom metalloproteinase (SVMP) class. The third peak was identified as a sphingolipid. Interestingly, the in vivo preclinical tests showed no significant differences in the effectiveness of the antivenoms. which could be due to the cross-immunogenicity or cross-reactivity between different toxins in the venom. According to our results, small variations in the venom composition of a species do not lead to a decrease in the efficacy of the polyvalent antivenom.

Toxicological analyses of the venoms of Nigerian vipers Echis ocellatus and Bitis arietans

BACKGROUND

Among the medically important snakes in Nigeria, Echis ocellatus and Bitis arietans have the most lethal venom. These venoms were classified according to the presence of snake venom metalloproteinases (SVMPs), snake venom phospholipase A2 (PLA2s), and snake venom serine proteases (SVSPs). Toxicological analyzes were performed to understand the significance of different protein families in venoms.

METHODS

Proteins were separated from venom using column chromatography. The skin and footpad of mice were used to determine hemorrhagic and edematogenic activities. Caprine blood plasma was used to test fibrinolytic activity in vitro.

RESULTS

The results showed that, compared to the crude venom, the SVMP fraction induced hemorrhagic effects with a diameter of 26.00 ± 1.00 mm in E. ocellatus and 21.33 ± 1.52 mm in B. arietans. Both SVSP and SVMP had anticoagulant effects; however, the SVSP fraction had a stronger effect, with a longer anticoagulation time of 30.00 ± 3.00 min in E. ocellatus and 26.00 ± 2.00 min in B. arietans. These main venom toxins, SVMPs, SVSPs, and PLA2, were found to have edema-forming effects that were optimal at 2 h after envenomation. PLA2s had the highest edema-inducing activity, with onset 30 min after envenomation.

CONCLUSIONS

Given the importance of SVMPs in altering the integrity of the membrane structure and impairing the blood coagulation system, an antivenom that can specifically neutralize its activity could inhibit the hemorrhage effects of the venoms.

A novel metalloproteinase-derived cryptide from Bothrops cotiara venom inhibits angiotensin-converting enzyme activity

Snake venoms are primarily composed of proteins and peptides, which selectively interact with specific molecular targets, disrupting prey homeostasis. Identifying toxins and the mechanisms involved in envenoming can lead to the discovery of new drugs based on natural peptide scaffolds. In this study, we used mass spectrometry-based peptidomics to sequence 197 peptides in the venom of Bothrops cotiara, including a novel 7-residue peptide derived from a snake venom metalloproteinase. This peptide, named Bc-7a, features a pyroglutamic acid at the N-terminal and a PFR motif at the C-terminal, homologous to bradykinin. Using FRET (fluorescence resonance energy transfer) substrate assays, we demonstrated that Bc-7a strongly inhibits the two domains of angiotensin converting enzyme (Ki < 1 μM). Our findings contribute to the repertoire of biologically active peptides from snake venoms capable of inhibiting angiotensin-converting enzyme (ACE), beyond current known structural motifs and precursors. In summary, we report a novel snake venom peptide with ACE inhibitory activity, suggesting its potential contribution to the hypotensive effect observed in envenomation.

Transcriptomic and proteomic analyses reveal the first occurrence of diverse toxin groups in Millepora alcicornis

Millepora alcicornis is a reef-forming cnidarian widely distributed in the Mexican Caribbean. Millepora species or "fire corals" inflict a painful stinging reaction in humans when touched. Even though hundreds of organic and polypeptide toxins have been characterized from sea anemones and jellyfish, there are few reports regarding the diversity of toxins synthesized by fire corals. Here, based on transcriptomic analysis of M. alcicornis, several predicted proteins that show amino acid sequence similarity to toxins were identified, including neurotoxins, metalloproteases, hemostasis-impairing toxins, serin proteases, cysteine-rich venom proteins, phospholipases, complement system-impairing toxins, phosphodiesterases, pore-forming toxins, and L-aminoacid oxidases. The soluble nematocyst proteome of this organism was shown to induce hemolytic, proteolytic, and phospholipase A2 effects by gel zymography. Protein bands or spots on 1D- and 2D-PAGE gels corresponding to zones of hemolytic and enzymatic activities were excised, subjected to in-gel digestion with trypsin, and analyzed by mass spectrometry. These proteins exhibited sequence homology to PLA2s, metalloproteinases, pore-forming toxins, and neurotoxins, such as actitoxins and CrTX-A. The complex array of venom-related transcripts that were identified in M. alcicornis, some of which are first reported in "fire corals", provide novel insight into the structural richness of Cnidarian toxins and their distribution among species. SIGNIFICANCE: Marine organisms are a promising source of bioactive compounds with valuable contributions in diverse fields such as human health, pharmaceuticals, and industrial application. Currently, not much attention has been paid to the study of fire corals, which possess a variety of molecules that exhibit diverse toxic effects and therefore have great pharmaceutical and biotechnological potential. The isolation and identification of novel marine-derived toxins by classical approaches are time-consuming and have low yields. Thus, next-generation strategies, like base-'omics technologies, are essential for the high-throughput characterization of venom compounds such as those synthesized by fire corals. This study moves the field forward because it provides new insights regarding the first occurrence of diverse toxin groups in Millepora alcicornis. The findings presented here will contribute to the current understanding of the mechanisms of action of Millepora toxins. This research also reveals important information related to the potential role of toxins in the defense and capture of prey mechanisms and for designing appropriate treatments for fire coral envenomation. Moreover, due to the lack of information on the taxonomic identification of Millepora, the insights presented here can advise the taxonomic classification of the species of this genus.

Snake venom disintegrins update: insights about new findings

Snake venom disintegrins are low molecular weight, non-enzymatic proteins rich in cysteine, present in the venom of snakes from the families Viperidae, Crotalidae, Atractaspididae, Elapidae, and Colubridae. This family of proteins originated in venom through the proteolytic processing of metalloproteinases (SVMPs), which, in turn, evolved from a gene encoding an A Disintegrin And Metalloprotease (ADAM) molecule. Disintegrins have a recognition motif for integrins in their structure, allowing interaction with these transmembrane adhesion receptors and preventing their binding to proteins in the extracellular matrix and other cells. This interaction gives disintegrins their wide range of biological functions, including inhibition of platelet aggregation and antitumor activity. As a result, many studies have been conducted in an attempt to use these natural compounds as a basis for developing therapies for the treatment of various diseases. Furthermore, the FDA has approved Tirofiban and Eptifibatide as antiplatelet compounds, and they are synthesized from the structure of echistatin and barbourin, respectively. In this review, we discuss some of the main functional and structural characteristics of this class of proteins and their potential for therapeutic use.

Cobra venom P-III class metalloproteinase atrase a induces inflammatory response and cell apoptosis in endothelial cells via its metalloproteinase domain

Snake venom metalloproteinases (SVMPs), which are a critical component of viperid and crotalid venoms, play various important roles in the pathogenesis of snakebite envenomation. The SVMPs from elapid venoms are not well elucidated, as compared with those from viperid and crotalid venoms. Atrase A is a nonhemorrhagic P-III SVMP purified from Naja atra venom that possesses only weak fibrinogenolytic activity. In our prior study, we found that atrase A detached adherent cells from the substrate. In this work, we investigated further the effect and mechanism of atrase A on endothelial cells. Oxidative damage, inflammatory mediators, apoptosis, and activation of the NF-κB and MAPK signaling pathways were measured after HMEC-1 cells were exposed to atrase A. The results showed that HMEC-1 cells released inflammatory mediators, exihibited oxidative damage and apoptosis after exposure to atrase A. The Western blot analysis results revealed that atrase A increased Bax/Bcl-2 and caspase-3 levels and activated the NF-κB and MAPK signaling pathways in endothelial cells. The effects on endothelial cells were nearly completely abolished after atrase A was treated with ethylenediamine tetraacetic acid. These results showed that atrase A led to an inflammatory response, cellular injury and apoptosis in endothelial cells, and this effect was due to its metalloproteinase domain. The study contributes to a better understanding of the structures and functions of cobra venom P-III class metalloproteinases.

Pictolysin-III, a Hemorrhagic Type-III Metalloproteinase Isolated from Bothrops pictus (Serpentes: Viperidae) Venom, Reduces Mitochondrial Respiration and Induces Cytokine Secretion in Epithelial and Stromal Cell Lines

From the venom of the Bothrops pictus snake, an endemic species from Peru, we recently have described toxins that inhibited platelet aggregation and cancer cell migration. In this work, we characterize a novel P-III class snake venom metalloproteinase, called pictolysin-III (Pic-III). It is a 62 kDa proteinase that hydrolyzes dimethyl casein, azocasein, gelatin, fibrinogen, and fibrin. The cations Mg²⁺ and Ca²⁺ enhanced its enzymatic activity, whereas Zn²⁺ inhibited it. In addition, EDTA and marimastat were also effective inhibitors. The amino acid sequence deduced from cDNA shows a multidomain structure that includes a proprotein, metalloproteinase, disintegrin-like, and cysteine-rich domains. Additionally, Pic-III reduces the convulxin- and thrombin-stimulated platelet aggregation and in vivo, it has hemorrhagic activity (DHM = 0.3 µg). In epithelial cell lines (MDA-MB-231 and Caco-2) and RMF-621 fibroblast, it triggers morphological changes that are accompanied by a decrease in mitochondrial respiration, glycolysis, and ATP levels, and an increase in NAD(P)H, mitochondrial ROS, and cytokine secretion. Moreover, Pic-III sensitizes to the cytotoxic BH3 mimetic drug ABT-199 (Venetoclax) in MDA-MB-231 cells. To our knowledge, Pic-III is the first SVMP reported with action on mitochondrial bioenergetics and may offer novel opportunities for promising lead compounds that inhibit platelet aggregation or ECM-cancer-cell interactions.

Venom-gland transcriptomics of the Malayan pit viper (Calloselasma rhodostoma) for identification, classification, and characterization of venom proteins

The Malayan pit viper (Calloselasma rhodostoma) is a hemotoxic snake widely found in Southeast Asia and is responsible for the majority of poisoning cases in this region, including Thailand. However, a comprehensive knowledge of the venom protein profile and classification, as well as novel venom proteins, of this viper is still limited. Recently, the detailed composition of several snake venoms has been discovered through the use of transcriptome analysis. Therefore, the aim of this study was to employ a next-generation sequencing platform and bioinformatics analysis to undertake venom-gland de novo transcriptomics of Malayan pit vipers. Furthermore, 21,272 functional coding genes were identified from 36,577 transcripts, of which 314 transcripts were identified as toxin proteins, accounting for 61.41% of total FPKM, which can be categorized into 22 toxin gene families. The most abundant are snake venom metalloproteinase kistomin (P0CB14) and zinc metalloproteinase/disintegrin (P30403), which account for 60.47% of total toxin FPKM and belong to the SVMP toxin family, followed by snake venom serine protease 1 (O13059) and Snaclec rhodocetin subunit beta (P81398), which account for 6.84% and 5.50% of total toxin FPKM and belong to the snake venom serine protease (SVSP) and Snaclec toxin family, respectively. Amino acid sequences of the aforementioned toxins were compared with those identified in other important medical hemotoxic snakes from Southeast Asia, including the Siamese Russell's viper (Daboia siamensis) and green pit viper (Trimeresurus albolabris), in order to analyze their protein homology. The results demonstrated that ranges of 58%-62%, 31%-60%, and 48%-59% identity was observed among the SVMP, Snaclec, and SVSP toxin families, respectively. Understanding the venom protein profile and classification is essential in interpreting clinical symptoms during human envenomation and developing potential therapeutic applications. Moreover, the variability of toxin families and amino acid sequences among related hemotoxic snakes found in this study suggests the use and development of universal antivenom for the treatment of envenomating patients is still challenging.

De Novo Venom Gland Transcriptome Assembly and Characterization for Calloselasma rhodostoma (Kuhl, 1824), the Malayan Pit Viper from Malaysia: Unravelling Toxin Gene Diversity in a Medically Important Basal Crotaline

In Southeast Asia, the Malayan Pit Viper (Calloselasma rhodostoma) is a venomous snake species of medical importance and bioprospecting potential. To unveil the diversity of its toxin genes, this study de novo assembled and analyzed the venom gland transcriptome of C. rhodostoma from Malaysia. The expression of toxin genes dominates the gland transcriptome by 53.78% of total transcript abundance (based on overall FPKM, Fragments Per Kilobase Million), in which 92 non-redundant transcripts belonging to 16 toxin families were identified. Snake venom metalloproteinase (SVMP, PI > PII > PIII) is the most dominant family (37.84% of all toxin FPKM), followed by phospholipase A₂ (29.02%), bradykinin/angiotensin-converting enzyme inhibitor-C-type natriuretic peptide (16.30%), C-type lectin (CTL, 10.01%), snake venom serine protease (SVSP, 2.81%), L-amino acid oxidase (2.25%), and others (1.78%). The expressions of SVMP, CTL, and SVSP correlate with hemorrhagic, anti-platelet, and coagulopathic effects in envenoming. The SVMP metalloproteinase domains encode hemorrhagins (kistomin and rhodostoxin), while disintegrin (rhodostomin from P-II) acts by inhibiting platelet aggregation. CTL gene homologues uncovered include rhodocytin (platelet aggregators) and rhodocetin (platelet inhibitors), which contribute to thrombocytopenia and platelet dysfunction. The major SVSP is a thrombin-like enzyme (an ancrod homolog) responsible for defibrination in consumptive coagulopathy. The findings provide insight into the venom complexity of C. rhodostoma and the pathophysiology of envenoming.

Rhomb-I, a P–I metalloproteinase from Lachesis muta rhombeata venom degrades vessel extra cellular matrix components and impairs platelet aggregation

Rhomb-I, a 23-kDa metalloproteinase was isolated from L. m. rhombeata venom. Its dimethylcasein proteolysis was abolished by metal chelators, and slightly enhanced by Ca²⁺ and Mg²⁺ ions, but inhibited by Co²⁺, Zn²⁺ and α2-macroglobulin. In aqueous solution, rhomb-I autoproteolyzed to a 20- and 11-kDa fragments at 37 °C. The amino acid sequence showed high homology with other snake venom metalloproteinases. Rhomb-I causes hemorrhage that may be ascribed to hydrolysis of essential basement membrane, extracellular matrix and plasma proteins. It preferentially cleaves the α-chains of fibrin (ogen). Rhomb-I inhibited convulxin- and von Willebrand factor (vWF)-induced aggregation on human platelets without significant effect on collagen-stimulated aggregation or other effectors. It digests vWF into a low-molecular-mass multimers of vWF and a rvWF-A1 domain to a 27-kDa fragment as revealed by western blotting with mouse anti-rvWF A1-domain IgG. Incubation of platelets with rhomb-I resulted in adhesion to and cleavage of platelet receptors glycoprotein (GP)Ibα and GPVI to release a 55-kDa soluble form. Both membrane glycoproteins GPIbα that binds vWF, together with GPVI which binds collagen, play a key role in mediating platelet adhesion/activation and can initiate (patho)physiological thrombus formation. Conclusions: rhomb-I is implicated in the pathophysiology of Lachesis envenoming by disrupting vasculature, hemostasis and platelet aggregation through impairing vWF-GPIb axis and blocking GPVI-collagen binding.

A rational in silico approach to identify inhibitors of Batroxrhagin from Bothrops atrox

Bothrops atrox venom comprises several types of bioactive molecules, enzymatic and non-enzymatic, among those, Batroxrhagin is the most predominant SVMP P-III enzyme, which are responsible for induction of local and systemic hemorrhage and muscle fibers damage, impairing regeneration. Due to great difficulties in establishing an antibothropic drug, new strategies must be addressed to achieve a more effective and efficient treatment. There are no studies of specific catalytic inhibitors of Batroxrhagin. However, there are in vitro studies that have described similar metalloprotease inhibitors. The inhibitor batimastat was used as a leading compound for the search and selection of similar candidates. This molecule is widely cited as a metalloprotease inhibitor and as an antimetastatic. In addition to batimastat-like molecules, four other reported metalloprotease inhibitors were included to compose the study's positive control group. Hence, 580 molecules were tested. The three-dimensional structure of B. atrox Batroxrhagin was predicted based on homologous structures using Modeller 9.20. Molecular docking calculation was performed using Autodock 4.2 and molecular surfaces and interactions were analyzed using Biovia/Discovery Studio 2017. Among 576 molecules, 42 similar to batismast resulted in a better energy of interaction than all positive controls, including batimastat itself. The batimastat-like molecules with lowest energy and positive controls were subjected to molecular dynamics for 30 ns in Gromacs 2019.4. This batimastat-like molecule produced better stability among all the Batroxrhagin-ligand complexes analyzed. Overall, the proposed compounds present justifiable evidence for future in vitro tests aiming to inhibit Batroxrhagin. Communicated by Ramaswamy H. Sarma.

Extracellular Vesicles from Bothrops jararaca Venom Are Diverse in Structure and Protein Composition and Interact with Mammalian Cells

Snake venoms are complex cocktails of non-toxic and toxic molecules that work synergistically for the envenoming outcome. Alongside the immediate consequences, chronic manifestations and long-term sequelae can occur. Recently, extracellular vesicles (EVs) were found in snake venom. EVs mediate cellular communication through long distances, delivering proteins and nucleic acids that modulate the recipient cell's function. However, the biological roles of snake venom EVs, including possible cross-organism communication, are still unknown. This knowledge may expand the understanding of envenoming mechanisms. In the present study, we isolated and characterized the EVs from Bothrops jararaca venom (Bj-EVs), giving insights into their biological roles. Fresh venom was submitted to differential centrifugation, resulting in two EV populations with typical morphology and size range. Several conserved EV markers and a subset of venom related EV markers, represented mainly by processing enzymes, were identified by proteomic analysis. The most abundant protein family observed in Bj-EVs was 5'-nucleotidase, known to be immunosuppressive and a low abundant and ubiquitous toxin in snake venoms. Additionally, we demonstrated that mammalian cells efficiently internalize Bj-EVs. The commercial antibothropic antivenom partially recognizes Bj-EVs and inhibits cellular EV uptake. Based on the proteomic results and the in vitro interaction assays using macrophages and muscle cells, we propose that Bj-EVs may be involved not only in venom production and processing but also in host immune modulation and long-term effects of envenoming.

Poly-Gly Region Regulates the Accessibility of Metal Binding Sites in Snake Venom Peptides

It is supposed that the presence of poly-His regions in close proximity to poly-Gly domains in snake venoms is related to their biological activity; poly-His/poly-Gly (pHpG) peptides inhibit the activity of metalloproteinases during venom storage via the chelation metal ions, necessary for their proper functioning. This work shows that only the histidyl residues from the N-terminal VDHDHDH motif (but not from the poly-His tag) were the primary Zn(II) binding sites and that the poly-Gly domain situated in the proximity of a central proline residue may play a regulatory role in venom gland protection. The proline induces a kink of the peptide, resulting in steric hindrance, which may modulate the accessibility of potential metal binding sites in the poly-His domain and may, in turn, be one of the regulators of Zn(II) accessibility in the venom gland and therefore a modulator of metalloproteinase activity during venom storage.

The proline induces a kink of the peptide, resulting in a steric hindrance, which may modulate the accessibility of potential metal binding sites in the poly-His domain and may, in turn, be one of the regulators of Zn(II) accessibility in the venom gland and therefore a modulator of metalloproteinase activity during venom storage.

The rise of genomics in snake venom research: recent advances and future perspectives

Snake venoms represent a danger to human health, but also a gold mine of bioactive proteins that can be harnessed for drug discovery purposes. The evolution of snakes and their venom has been studied for decades, particularly via traditional morphological and basic genetic methods alongside venom proteomics. However, while the field of genomics has matured rapidly over the past 2 decades, owing to the development of next-generation sequencing technologies, snake genomics remains in its infancy. Here, we provide an overview of the state of the art in snake genomics and discuss its potential implications for studying venom evolution and toxinology. On the basis of current knowledge, gene duplication and positive selection are key mechanisms in the neofunctionalization of snake venom proteins. This makes snake venoms important evolutionary drivers that explain the remarkable venom diversification and adaptive variation observed in these reptiles. Gene duplication and neofunctionalization have also generated a large number of repeat sequences in snake genomes that pose a significant challenge to DNA sequencing, resulting in the need for substantial computational resources and longer sequencing read length for high-quality genome assembly. Fortunately, owing to constantly improving sequencing technologies and computational tools, we are now able to explore the molecular mechanisms of snake venom evolution in unprecedented detail. Such novel insights have the potential to affect the design and development of antivenoms and possibly other drugs, as well as provide new fundamental knowledge on snake biology and evolution.

The potential of phenolic acids in therapy against snakebites: A review

Ophidism is a serious health problem worldwide and is included in the World Health Organization's (WHO's) list of Neglected Tropical Diseases. Although snakebite envenoming requires emergency treatment, currently the only treatment recommended by WHO is serotherapy, which has some disadvantages such as low access to the rural population, low effectiveness in neutralizing local effects, and high cost. In this context, new alternatives for the treatment of snakebites are required. The use of plant-derived compounds to inhibit the effects caused by snake venoms has been the object of a number of studies in recent years. This review aims to provide an up-to-date overview of the use of phenolic acids with therapeutic application against envenomation by snakes of different species. In this sense, structural analysis in silico and biological activities in vivo and in vitro were reported. The acids were subdivided into derivatives of benzoic and cinnamic acids, with derivatives of cinnamic acids being the most studied. Studies have revealed that these compounds are capable of inhibiting local and systemic effects induced by envenomation, and structural analyses indicate that the acids interact with important sites responsible for the action of toxins. Thus, it was reported that phenolic acids showed antiophidic potential, providing insights for future research to develop complementary drugs for the treatment of snakebites.

Venom proteomic analysis of medically important Nigerian viper Echis ocellatus and Bitis arietans snake species

Snakebite envenoming remains a neglected tropical disease which poses severe health hazard, especially for the rural inhabitants in Africa. In Nigeria, vipers are responsible for the highest number of deaths. Hydrophilic interaction liquid chromatography coupled with LC-MS/MS was used to analyze the crude venoms of Echis ocellatus (Carpet viper) and Bitis arietans (Puff adder) in order to understand their venom proteomic identities. Results obtained revealed that gel-free proteomic analysis of the crude venoms led to the identification of 85 and 79 proteins, respectively. Seventy-eight (78) proteins were common between the two snake species with a 91.8% similarity score. The identified proteins belong to 18 protein families in E. ocellatus and 14 protein families in B. arietans. Serine proteases (22.31%) and metalloproteinases (21.06%) were the dominant proteins in the venom of B. arietans; while metalloproteinases (34.84%), phospholipase A₂s (21.19%) and serine proteases (15.50%) represent the major toxins in the E. ocellatus venom. Other protein families such as three-finger toxins and cysteine-rich venom proteins were detected in low proportions. This study provides an insight into the venom proteomic analysis of the two Nigerian viper species, which could be useful in identifying the toxin families to be neutralized in case of envenomation.

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Venom proteomic of Nigeria's most medically important snakes is presented.

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SVMP, SVSP and PLA₂ were the major toxin families in E. ocellatus and B. arietans.

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The venom proteomes of these vipers displayed 91.8% similarity in composition.

Proteomic Identification and Quantification of Snake Venom Biomarkers in Venom and Plasma Extracellular Vesicles

The global exploration of snakebites requires the use of quantitative omics approaches to characterize snake venom as it enters into the systemic circulation. These omics approaches give insights into the venom proteome, but a further exploration is warranted to analyze the venom-reactome for the identification of snake venom biomarkers. The recent discovery of extracellular vesicles (EVs), and their critical cellular functions, has presented them as intriguing sources for biomarker discovery and disease diagnosis. Herein, we purified EV’s from the snake venom (svEVs) of Crotalus atrox and C. oreganus helleri, and from plasma of BALB/c mice injected with venom from each snake using EVtrap in conjunction with quantitative mass spectrometry for the proteomic identification and quantification of svEVs and plasma biomarkers. Snake venom EVs from C. atrox and C. o. helleri were highly enriched in 5′ nucleosidase, L-amino acid oxidase, and metalloproteinases. In mouse plasma EVs, a bioinformatic analysis for revealed upregulated responses involved with cytochrome P450, lipid metabolism, acute phase inflammation immune, and heat shock responses, while downregulated proteins were associated with mitochondrial electron transport, NADH, TCA, cortical cytoskeleton, reticulum stress, and oxidative reduction. Altogether, this analysis will provide direct evidence for svEVs composition and observation of the physiological changes of an envenomated organism.

Proteo-Trancriptomic Analyses Reveal a Large Expansion of Metalloprotease-Like Proteins in Atypical Venom Vesicles of the Wasp Meteorus pulchricornis (Braconidae)

Meteorus pulchricornis (Ichneumonoidea, Braconidae) is an endoparasitoid wasp of lepidopteran caterpillars. Its parasitic success relies on vesicles (named M. pulchricornis Virus-Like Particles or MpVLPs) that are synthesized in the venom gland and injected into the parasitoid host along with the venom during oviposition. In order to define the content and understand the biogenesis of these atypical vesicles, we performed a transcriptome analysis of the venom gland and a proteomic analysis of the venom and purified MpVLPs. About half of the MpVLPs and soluble venom proteins identified were unknown and no similarity with any known viral sequence was found. However, MpVLPs contained a large number of proteins labelled as metalloproteinases while the most abundant protein family in the soluble venom was that of proteins containing the Domain of Unknown Function DUF-4803. The high number of these proteins identified suggests that a large expansion of these two protein families occurred in M. pulchricornis. Therefore, although the exact mechanism of MpVLPs formation remains to be elucidated, these vesicles appear to be “metalloproteinase bombs” that may have several physiological roles in the host including modifying the functions of its immune cells. The role of DUF4803 proteins, also present in the venom of other braconids, remains to be clarified.

The venom proteome of three common scyphozoan jellyfishes (Chrysaora caliparea, Cyanea nozakii and Lychnorhiza malayensis) (Cnidaria: Scyphozoa) from the coastal waters of India

The jellyfish venom stored in nematocysts contains highly toxic compounds comprising of polypeptides, enzymes and other proteins, which form their chemical defence armoury against predators. We have characterized the proteome of crude venom extract from three bloom-forming scyphozoan jellyfish along the south-west coast of India, Chrysaora caliparea, Cyanea nozakii and Lychnorhiza malayensis using a Quadrupole-Time of Flight (Q/TOF) mass spectrometry analysis. The most abundant toxin identified from Chrysaora caliparea and Lychnorhiza malayensis is similar to the pore-forming toxins and metalloproteinases. A protective antioxidant enzyme called peroxiredoxin was found abundantly in Cyanea nozakii. Metalloproteinase identified from the C. caliparea shows similarity with the venom of pit viper (Bothrops pauloensis), while that of L. malayensis was similar to the venom of snakes such as the Bothrops insularis and Bothrops asper. Kininogen-1 is a secreted protein, identified for the first time from the jellyfish L. malayensis. The proteome analysis of Cyanea nozakii, Chrysaora caliparea and Lychnorhiza malayensis contained 20, 12, 8 unique proteins, respectively. Our study characterized the proteome map of crude venom extract from L. malayensis and C. caliparea for the first time, and the venom profile is compared with published information elsewhere. Proteomic data from this study has been made available in the public domain.

Clinical implications of differential procoagulant toxicity of the palearctic viperid genus Macrovipera, and the relative neutralization efficacy of antivenoms and enzyme inhibitors

Species within the viperid genus Macrovipera are some of the most dangerous snakes in the Eurasian region, injecting copious amounts of potent venom. Despite their medical importance, the pathophysiological actions of their venoms have been neglected. Particularly poorly known are the coagulotoxic effects and thus the underlying mechanisms of lethal coagulopathy. In order to fill this knowledge gap, we ascertained the effects of venom upon human plasma for Macrovipera lebetina cernovi, M. l. lebetina, M. l. obtusa, M. l. turanica, and M. schweizeri using diverse coagulation analysing protocols. All five were extremely potent in their ability to promote clotting but varied in their relative activation of Factor X, being equipotent in this study to the venom of the better studied, and lethal, species Daboia russelii. The Insoserp European viper antivenom was shown to be highly effective against all the Macrovipera venoms, but performed poorly against the D. russelii venom. Reciprocally, while Daboia antivenoms performed well against D. russelii venom, they failed against Macrovipera venom. Thus despite the two genera sharing a venom phenotype (Factor X activation) driven by the same toxin type (P-IIId snake venom metalloproteases), the surface biochemistries of the toxins differed significantly enough to impede antivenom cross- neutralization. The differences in venom biochemistry were reflected in coagulation co-factor dependence. While both genera were absolutely dependent upon calcium for the activation of Factor X, dependence upon phospholipid varied. The Macrovipera venoms had low levels of dependence upon phospholipid while the Daboia venom was three times more dependent upon phospholipid for the activation of Factor X. This suggests that the sites on the molecular surface responsible for phospholipid dependence, are the same differential sites that prevent inter-genera antivenom cross- neutralization. Due to cold-chain requirements, antivenoms may not be stocked in rural settings where the need is at the greatest. Thus we tested the efficacy of enzyme inhibitor Prinomastat as a field-deployable treatment to stabilise patients while being transported to antivenom stocks, and showed that it was extremely effective in blocking the Factor X activating pathophysiological actions. Marimastat however was less effective. These results thus not only shed light on the coagulopathic mechanisms of Macrovipera venoms, but also provide data critical for evidence-based design of snakebite management strategies.

Proteomic Investigations of Two Pakistani Naja Snake Venoms Species Unravel the Venom Complexity, Posttranslational Modifications, and Presence of Extracellular Vesicles

Latest advancement of omics technologies allows in-depth characterization of venom compositions. In the present work we present a proteomic study of two snake venoms of the genus Naja i.e., Naja naja (black cobra) and Naja oxiana (brown cobra) of Pakistani origin. The present study has shown that these snake venoms consist of a highly diversified proteome. Furthermore, the data also revealed variation among closely related species. High throughput mass spectrometric analysis of the venom proteome allowed to identify for the N. naja venom 34 protein families and for the N. oxiana 24 protein families. The comparative evaluation of the two venoms showed that N. naja consists of a more complex venom proteome than N. oxiana venom. Analysis also showed N-terminal acetylation (N-ace) of a few proteins in both venoms. To the best of our knowledge, this is the first study revealing this posttranslational modification in snake venom. N-ace can shed light on the mechanism of regulation of venom proteins inside the venom gland. Furthermore, our data showed the presence of other body proteins, e.g., ankyrin repeats, leucine repeats, zinc finger, cobra serum albumin, transferrin, insulin, deoxyribonuclease-2-alpha, and other regulatory proteins in these venoms. Interestingly, our data identified Ras-GTpase type of proteins, which indicate the presence of extracellular vesicles in the venom. The data can support the production of distinct and specific anti-venoms and also allow a better understanding of the envenomation and mechanism of distribution of toxins. Data are available via ProteomeXchange with identifier PXD018726.

Inhibition of platelet aggregation and blood coagulation by a P-III class metalloproteinase purified from Naja atra venom

Snake venom metalloproteinases (SVMPs) are an important component in viperid and crotalid venoms, and these SVMPs play important and versatile roles in the pathogenesis of snakebite envenoming. The SVMPs from elapid venoms are not well elucidated compared with those from viperid and crotalid venoms. Atrase B is a nonhemorrhagic P-III SVMP purified from the Naja atra venom, which possesses a weak fibrinogenolytic activity. In this paper, the activity and mechanism of atrase B against platelet aggregation and blood coagulation were investigated. The in vitro assay showed that atrase B remarkably inhibited ristocetin- and thrombin-induced platelet aggregation by cleavage of the platelet membrane glycoprotein Ib, and the coagulation of normal human plasma, which may be caused by inhibiting coagulation factor VIII predominantly. When atrase B was intravenously injected into rats at doses of 0.05 and 0.30 mg/kg, the activated partial thromboplastin and the thrombin times were significantly prolonged in a dose-dependent manner. Similarly, the fibrinogen level decreased, but only a high dose of atrase B showed remarkable activity against platelet aggregation. Results suggested that anticoagulation was a more important function of atrase B compared with its activity against platelet aggregation. These results indicated that atrase B may play an important role in the anticoagulant properties of Naja atra venom. In addition, atrase B may be a potent anticoagulant agent because its effectiveness in vivo against platelet aggregation and blood coagulation.

Differential coagulotoxicity of metalloprotease isoforms from Bothrops neuwiedi snake venom and consequent variations in antivenom efficacy

Bothrops (lance-head pit vipers) venoms are rich in weaponised metalloprotease enzymes (SVMP). These toxic enzymes are structurally diverse and functionally versatile. Potent coagulotoxicity is particularly important for prey capture (via stroke-induction) and relevant to human clinical cases (due to consumption of clotting factors including the critical depletion of fibrinogen). In this study, three distinct isoforms of P-III class SVMPs (IC, IIB and IIC), isolated from Bothrops neuwiedi venom, were evaluated for their differential capacities to affect hemostasis of prey and human plasma. Furthermore, we tested the relative antivenom neutralisation of effects upon human plasma. The toxic enzymes displayed differential procoagulant potency between plasma types, and clinically relevant antivenom efficacy variations were observed. Of particular importance was the confirmation the antivenom performed better against prothrombin activating toxins than Factor X activating toxins, which is likely due to the greater prevalence of the former in the immunising venoms used for antivenom production. This is clinically relevant as the enzymes displayed differential potency in this regard, with one (IC) in particular being extremely potent in activating Factor X and thus was correspondingly poorly neutralised. This study broadens the current understanding about the adaptive role of the SVMPs, as well as highlights how the functional diversity of SVMP isoforms can influence clinical outcomes. Key Contribution: Our findings shed light upon the hemorrhagic and coagulotoxic effects of three SVMPs of the P-III class, as well as the coagulotoxic effects of SVMPs on human, avian and amphibian plasmas. Antivenom neutralised prothrombin-activating isoforms better than Factor X activating isoforms.

Fast venomic analysis of Crotalus durissus terrificus from northeastern Argentina

The complete knowledge of the toxins that make up venoms is the base for the treatment of snake accidents victims and the selection of specimens for the preparation of venom pools for antivenom production. In this work, we used a fast and direct venomics approach to identify the toxin families in the C.d. terrificus venom, a Southern American Neotropical rattlesnake. The RP-HPLC separation profile of pooled venom from adult specimens followed by mass spectrometry analysis revealed that C.d. terrificus' venom proteome is composed of 12 protein families, which are unevenly distributed in the venom, e.g., there are few major proteins in the venom's composition phospholipase A₂, serine proteinase, crotamine and L-amino acid oxidase. At the same time, the proteome analysis revealed a small set of proteins with low quantity (less than 1.5%), both enzymes (metaloprotease, phospholipase B and 5'-nucleotidase) and proteins (Bradykinin potentiating and C-type natriuretic peptides, C-type lectin convulxin and nerve growth factor). To sum up, this research is the first venomic report of C.d.terrificus venom from Argentina. This proved to be crotamine positive venom that has a lower metalloprotease content than C.d. terrificus venoms from other regions. This information could be used in the discovery of future pharmacological agents or targets in antivenom therapy.

ICP-MS characterization of seven North American snake venoms

Snake venoms are inherently complex. They are mixtures of multiple enzymes, peptides, lipids, carbohydrates, nucleosides, and metal ions. Metal ions make up a small portion of a snake's venom but play outsized roles in enzyme function and stability. Unlike enzyme primary structure, which is easily predicted from genomic sequences, a venom's metal ion content must be measured directly. We leveraged the high throughput and sensitivity of inductively coupled plasma mass spectrometry to analyze the metal ion content of seven North American snake venoms. All venoms were collected from snakes reared at one location, so we could discount variation from environmental or geographical factors. We profiled 71 metal isotopes. Selenium isotopes were consistently high across all venoms tested. When each venom's toxicity was graphed as a function of each different metal isotope, the only strong relationships between metal content and toxicity were for magnesium isotopes.

Venom Systems as Models for Studying the Origin and Regulation of Evolutionary Novelties

A central goal in biology is to determine the ways in which evolution repeats itself. One of the most remarkable examples in nature of convergent evolutionary novelty is animal venom. Across diverse animal phyla, various specialized organs and anatomical structures have evolved from disparate developmental tissues to perform the same function, that is, produce and deliver a cocktail of potent molecules to subdue prey or predators. Venomous organisms therefore offer unique opportunities to investigate the evolutionary processes of convergence of key adaptive traits, and the molecular mechanisms underlying the emergence of novel genes, cells, and tissues. Indeed, some venomous species have already proven to be highly amenable as models for developmental studies, and recent work with venom gland organoids provides manipulatable systems for directly testing important evolutionary questions. Here, we provide a synthesis of the current knowledge that could serve as a starting point for the establishment of venom systems as new models for evolutionary and molecular biology. In particular, we highlight the potential of various venomous species for the study of cell differentiation and cell identity, and the regulatory dynamics of rapidly evolving, highly expressed, tissue-specific, gene paralogs. We hope that this review will encourage researchers to look beyond traditional study organisms and consider venom systems as useful tools to explore evolutionary novelties.

Natural Inhibitors of Snake Venom Metalloproteinases

Snakebites are a hazard in the tropical world. Although antivenom therapy is effective, it is beset with inherent drawbacks. A better understanding of the major components of snake venoms and their neutralisation will help in improving snakebite treatment. Snake venom metalloproteinases (SVMPs) are responsible for severe haemorrhage, the inhibition of coagulation and platelet aggregation, observed in the victims of snakebite envenoming. Inhibitors from various sources including medicinal plants, animal venoms, and sera are sought to block the pharmacological functions of SVMPs. In this review, we describe the interaction of natural inhibitors with SVMPs. To understand their inhibitory mechanisms, we focussed on the complex structures of these inhibitors and SVMPs. There are three distinct classes of inhibitors; namely, chelators, competitive inhibitors, and non-competitive inhibitors. A small number of inhibitors show their anti-hemorrhagic activity in invivo animal models in treatment mode, but most studies evaluate either invitro neutralisation of enzymatic activity or invivo effects in pre-incubation protocols. We propose the distinct strategies and limitations to design either broad-spectrum or highly selective SVMP inhibitors. The goal of designing broad-spectrum inhibitors against SVMPs capable of effective treatment of snakebites without toxicity has been elusive, probably because of the narrow molecular footprint of inhibitors against a large number of SVMPs with distinct molecular surfaces. Our ability to design highly selective inhibitors is limited by the lack of information of interactions between selective inhibitors and SVMPs. Comparisons of structures of hemorrhagic and non-hemorrhagic SVMPs revealed different distributions of electric charge on the surface of SVMPs, which may be exploited to design specific inhibitors. The specific inhibitors may also be useful to identify target molecules of the SVMPs and help to understand their mechanism of action.

Omics Technologies for Profiling Toxin Diversity and Evolution in Snake Venom: Impacts on the Discovery of Therapeutic and Diagnostic Agents

Snake venoms are primarily composed of proteins and peptides, and these toxins have developed high selectivity to their biological targets. This makes venoms interesting for exploration into protein evolution and structure-function relationships. A single venom protein superfamily can exhibit a variety of pharmacological effects; these variations in activity originate from differences in functional sites, domains, posttranslational modifications, and the formations of toxin complexes. In this review, we discuss examples of how the major venom protein superfamilies have diversified, as well as how newer technologies in the omics fields, such as genomics, transcriptomics, and proteomics, can be used to characterize both known and unknown toxins.Because toxins are bioactive molecules with a rich diversity of activities, they can be useful as therapeutic and diagnostic agents, and successful examples of toxin applications in these areas are also reviewed. With the current rapid pace of technology, snake venom research and its applications will only continue to expand.

Impact of El Niño-Southern Oscillation 2015-2016 on the soluble proteomic profile and cytolytic activity of Millepora alcicornis ("fire coral") from the Mexican Caribbean

Reef-forming cnidarians are extremely susceptible to the “bleaching” phenomenon caused by global warming. The effect of elevated seawater temperature has been extensively studied on Anthozoans; however, to date the impact of thermal stress on the expression of genes and proteins in Hydrozoan species has not been investigated. The present study aimed to determine the differential proteomic profile of Millepora alcicornis, which inhabits the Mexican Caribbean, in response to the El Niño-Southern Oscillation 2015–2016. Additionally, the cytolytic activity of the soluble proteomes obtained from normal and bleached M. alcicornis was assessed. Bleached specimens showed decreased symbiont’s density and chlorophyll a and c2 levels. After bleaching, we observed a differential expression of 17 key proteins, tentatively identified as related to exocytosis, calcium homeostasis, cytoskeletal organization, and potential toxins, including a metalloprotease, a phospholipase A2 (PLA2), and an actitoxin. Although, some of the differentially expressed proteins included potential toxins, the hemolytic, PLA2, and proteolytic activities elicited by the soluble proteomes from bleached and normal specimens were not significantly different. The present study provides heretofore-unknown evidence that thermal stress produces a differential expression of proteins involved in essential cellular processes of Hydrozoan species. Even though our results showed an over-expression of some potential toxin-related proteins, the cytolytic effect (as assessed by hemolytic, PLA2, and caseinolytic activities) was not increased in bleached M. alcicornis, which suggests that the cytolysis is mainly produced by toxins whose expression was not affected by temperature stress. These findings allow hypothesizing that this hydrocoral is able to prey heterotrophically when suffering from moderate bleaching, giving it a better chance to withstand the effects of high temperature.

A Single Mutation Unlocks Cascading Exaptations in the Origin of a Potent Pitviper Neurotoxin

Evolutionary innovations and complex phenotypes seemingly require an improbable amount of genetic change to evolve. Rattlesnakes display two dramatically different venom phenotypes. Type I venoms are hemorrhagic with low systemic toxicity and high expression of tissue-destroying snake venom metalloproteinases. Type II venoms are highly neurotoxic and lack snake venom metalloproteinase expression and associated hemorrhagic activity. This dichotomy hinges on Mojave toxin (MTx), a phospholipase A2 (PLA2) based β-neurotoxin expressed in Type II venoms. MTx is comprised of a nontoxic acidic subunit that undergoes extensive proteolytic processing and allosterically regulates activity of a neurotoxic basic subunit. Evolution of the acidic subunit presents an evolutionary challenge because the need for high expression of a nontoxic venom component and the proteolytic machinery required for processing suggests genetic changes of seemingly little immediate benefit to fitness. We showed that MTx evolved through a cascading series of exaptations unlocked by a single nucleotide change. The evolution of one new cleavage site in the acidic subunit unmasked buried cleavage sites already present in ancestral PLA2s, enabling proteolytic processing. Snake venom serine proteases, already present in the venom to disrupt prey hemostasis, possess the requisite specificities for MTx acidic subunit proteolysis. The dimerization interface between MTx subunits evolved by exploiting a latent, but masked, hydrophobic interaction between ancestral PLA2s. The evolution of MTx through exaptation of existing functional and structural features suggests complex phenotypes that depend on evolutionary innovations can arise from minimal genetic change enabled by prior evolution.

Arthropod venoms: Biochemistry, ecology and evolution

Comprising of over a million described species of highly diverse invertebrates, Arthropoda is amongst the most successful animal lineages to have colonized aerial, terrestrial, and aquatic domains. Venom, one of the many fascinating traits to have evolved in various members of this phylum, has underpinned their adaptation to diverse habitats. Over millions of years of evolution, arthropods have evolved ingenious ways of delivering venom in their targets for self-defence and predation. The morphological diversity of venom delivery apparatus in arthropods is astounding, and includes extensively modified pedipalps, tail (telson), mouth parts (hypostome), fangs, appendages (maxillulae), proboscis, ovipositor (stinger), and hair (urticating bristles). Recent investigations have also unravelled an astonishing venom biocomplexity with molecular scaffolds being recruited from a multitude of protein families. Venoms are a remarkable bioresource for discovering lead compounds in targeted therapeutics. Several components with prospective applications in the development of advanced lifesaving drugs and environment friendly bio-insecticides have been discovered from arthropod venoms. Despite these fascinating features, the composition, bioactivity, and molecular evolution of venom in several arthropod lineages remains largely understudied. This review highlights the prevalence of venom, its mode of toxic action, and the evolutionary dynamics of venom in Arthropoda, the most speciose phylum in the animal kingdom.

Comparative Profiling of Three Atheris Snake Venoms: A. squamigera, A. nitschei and A. chlorechis

A proteomic and transcriptomic comparative analysis of the venoms of three Atheris species (A. squamigera, A. nitschei and A. chlorechis) was carried out by size exclusion liquid chromatography, gel electrophoresis, mass spectrometry, and mRNA sequencing. The improved proteomic profiling utilised in this work was combined with transcript studies, advancing our insights into venom composition, protein distribution and inter-species variation among the three bush vipers. Crude venoms of all three samples contained at least 10-20 protein components, ranging in size from ≤ 3 to > 98 kDa. Both approaches yielded converging overall information, pointing to phospholipases, disintegrins, serine proteases and metalloproteases as the major toxin classes, which are likely to explain the local and systemic symptoms observed in envenomation by Atheris genus. Being considered as the main factors involved in the distinct venom-induced pathologies, these identified snake venom proteins are of particular interest in terms of understanding their physiological and biological function as well as for their contribution in potential medical treatments.

Purification and enzymatic characterization of a novel metalloprotease from Lachesis muta rhombeata snake venom

Background

Lachesis muta rhombeata (Lmr) is the largest venomous snake in Latin America and its venom contains mainly enzymatic components, such as serine and metalloproteases, L-amino acid oxidase and phospholipases A₂. Metalloproteases comprise a large group of zinc-dependent proteases that cleave basement membrane components such as fibronectin, laminin and collagen type IV. These enzymes are responsible for local and systemic changes, including haemorrhage, myonecrosis and inflammation. This study aimed the isolation and enzymatic characterization of the first metalloprotease (Lmr-MP) from Lmr venom (LmrV).

Methods and results

Lmr-MP was purified through two chromatographic steps and submitted to enzymatic characterization. It showed proteolytic activity on azocasein with maximum activity at pH 7.0–9.0. It was inhibited by EDTA (a metal chelator that removes zinc, which is essential for enzymatic activity) and no effect was observed with PMSF, iodoacetic acid or pepstatin (inhibitors of serine, cysteine and aspartyl proteases, respectively). Ca²⁺, Mg²⁺ and Ba²⁺ ions increased its activity, while Al³⁺, Cu²⁺, Ni²⁺ and Zn²⁺ inhibited it. Additionally, ZnCl₂ showed a dose dependent inhibition of the enzyme. Lmr-MP activity was also evaluated upon chromogenic substrates for plasma kallikrein (S-2302), plasmin and streptokinase-activated plasminogen (S-2251) and Factor Xa (S-2222) showing the highest activity on S-2302. The activity in different solutions (5 mM or 50 mM ammonium bicarbonate, pH 7.8; 0.1% trifluoroacetic acid + 50% acetonitrile; phosphate buffer saline, pH 7.4; 50 mM sodium acetate, pH 4.0 or ammonium acetate pH 4.5) was also evaluated and the results showed that its activity was abolished at acidic pHs. Its molecular mass (22,858 Da) was determined by MALDI-TOF and about 90% of its primary structure was verified by high-resolution mass spectrometry using HCD and ETD fragmentations and database search against the sequence of closely related species. It is a novel enzyme which shared high identity with other snake venom metalloproteases (svMPs) belonging to the P-I group.

Conclusion

The purification procedure achieved a novel pure highly active metalloprotease from LmrV. This new molecule can help to understand the metalloproteases mechanisms of action, the Lachesis envenoming, as well as to open new perspectives for its use as therapeutic tools.

Snake Venom Extracellular vesicles (SVEVs) reveal wide molecular and functional proteome diversity

Proteins constitute almost 95% of snake venom's dry weight and are produced and released by venom glands in a solubilized form during a snake bite. These proteins are responsible for inducing several pharmacological effects aiming to immobilize and initiate the pre-digestion of the prey. This study shows that proteins can be secreted and confined in snake venom extracellular vesicles (SVEVs) presenting a size distribution between 50 nm and 500 nm. SVEVs isolated from lyophilized venoms collected from four different species of snakes (Agkistrodon contortrix contortrix, Crotalus atrox, Crotalus viridis and Crotalus cerberus oreganus) were analyzed by mass spectrometry-based proteomic, which allowed the identification of proteins belonging to eight main functional protein classes such as SVMPs, serine proteinases, PLA₂, LAAO, 5'nucleotidase, C-type lectin, CRISP and Disintegrin. Biochemical assays indicated that SVEVs are functionally active, showing high metalloproteinase and fibrinogenolytic activity besides being cytotoxic against HUVEC cells. Overall, this study comprehensively depicts the protein composition of SVEVs for the first time. In addition, the molecular function of some of the described proteins suggests a central role for SVEVs in the cytotoxicity of the snake venom and sheds new light in the envenomation process.

Impaired expression of CXCL5 and matrix metalloproteinases in the lungs of mice with high susceptibility to Streptococcus pneumoniae infection

Introduction

Streptococcus pneumoniae colonizes the nasopharynx of healthy individuals establishing a commensal relationship with the host. In some conditions, bacteria invade the lower respiratory tract and innate immune responses are crucial to avoid diseases such as pneumonia, sepsis, or meningitis.

Methods

Here, we compared the susceptibility to pneumococcal respiratory infection of two outbred mouse lines, AIRmin and AIRmax, selected for low or high acute inflammatory responses, respectively.

Results

AIRmin mice showed increased susceptibility to infection with different pneumococcal serotypes, when compared to AIRmax. Significant higher numbers of alveolar macrophages expressing the CD206 mannose receptor were observed in AIRmin mice when compared to AIRmax mice. Despite this difference, secretion of several cytokines and chemokines in the respiratory tract of AIRmin and AIRmax mice, after infection, was similar. The only exception was CXCL5, which was highly induced after pneumococcal infection in AIRmax mice but not in AIRmin mice. Reduced expression of the matrix metalloproteinases (MMP) 2, 3, 8, and 9, as well as reduced activities of MMPs were also observed in the lungs of AIRmin mice, after infection. Such impaired responses may have contributed to the low influx of neutrophils observed in the airways of these mice. Finally, high percentages of macrophages and neutrophils in apoptosis or necrosis, at the site of infection, were also observed in AIRmin mice, suggesting that leukocyte functionality is also compromised.

Conclusions

Our results indicate that CXCL5 and MMPs contribute to the resistance to pneumococcal infection in mice.