Purification and functional characterisation of rhinocerase, a novel serine protease from the venom of Bitis gabonica rhinoceros

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.

The Clot Thickens: Differential Coagulotoxic and Cardiotoxic Activities of Anguimorpha Lizard Venoms

Despite their evolutionary novelty, lizard venoms are much less studied in comparison to the intense research on snake venoms. While the venoms of helodermatid lizards have long been assumed to be for defensive purposes, there is increasing evidence of toxic activities more useful for predation than defence (such as paralytic neurotoxicity). This study aimed to ascertain the effects of Heloderma, Lanthanotus, and Varanus lizard venoms on the coagulation and cardiovascular systems. Anticoagulant toxicity was demonstrated for the Varanus species studied, with the venoms prolonging clotting times in human and bird plasma due to the destructive cleavage of fibrinogen. In contrast, thromboelastographic analyses on human and bird plasmas in this study demonstrated a procoagulant bioactivity for Heloderma venoms. A previous study on Heloderma venom using factor-depleted plasmas as a proxy model suggested a procoagulant factor was present that activated either Factor XI or Factor XII, but could not ascertain the precise target. Our activation studies using purified zymogens confirmed FXII activation. Comparisons of neonate and adult H. exasperatum, revealed the neonates to be more potent in the ability to activate FXII, being more similar to the venom of the smaller species H. suspectum than the adult H. exasperatum. This suggests potent FXII activation a basal trait in the genus, present in the small bodied last common ancestor. This also indicates an ontogenetic difference in prey preferences in the larger Heloderma species paralleing the change in venom biochemistry. In addition, as birds lack Factor XII, the ability to clot avian plasma suggested an additional procoagulant site of action, which was revealed to be the activation of Factor VII, with H. horridum being the most potent. This study also examined the effects upon the cardiovascular system, including the liberation of kinins from kininogen, which contributes to hypotension induction. This form of toxicity was previously described for Heloderma venoms, and was revealed in this study was to also be a pathophysiological effect of Lanthanotus and Varanus venoms. This suggests that this toxic activity was present in the venom of the last common ancestor of the anguimorph lizards, which is consistent with kallikrein enzymes being a shared toxin trait. This study therefore uncovered novel actions of anguimorph lizard venoms, not only contributing to the evolutionary biology body of knowledge but also revealing novel activities to mine for drug design lead compounds.

Emerging anticancer potential and mechanisms of snake venom toxins: A review

Animal-derived venom, like snake venom, has been proven to be valuable natural resources for the drug development. Previously, snake venom was mainly investigated in its pharmacological activities in regulating coagulation, vasodilation, and cardiovascular function, and several marketed cardiovascular drugs were successfully developed from snake venom. In recent years, snake venom fractions have been demonstrated with anticancer properties of inducing apoptotic and autophagic cell death, restraining proliferation, suppressing angiogenesis, inhibiting cell adhesion and migration, improving immunity, and so on. A number of active anticancer enzymes and peptides have been identified from snake venom toxins, such as L-amino acid oxidases (LAAOs), phospholipase A2 (PLA2), metalloproteinases (MPs), three-finger toxins (3FTxs), serine proteinases (SPs), disintegrins, C-type lectin-like proteins (CTLPs), cell-penetrating peptides, cysteine-rich secretory proteins (CRISPs). In this review, we focus on summarizing these snake venom-derived anticancer components on their anticancer activities and underlying mechanisms. We will also discuss their potential to be developed as anticancer drugs in the future.

Untangling interactions between Bitis vipers and their prey using coagulotoxicity against diverse vertebrate plasmas

Venom is a key evolutionary innovation which plays a primary role in prey subjugation by venomous snakes. However, while there is a growing body of literature indicating the composition and activity of snake venoms is under strong natural selection driven by differences in prey physiology, the majority of studies have historically focussed on the activity of snake venoms with regards only towards human or mammalian physiologies. This study aimed to use clotting assays measuring both time and strength of clotting to characterise the coagulotoxic activity of venoms from a taxonomically, morphologically, and ecologically diverse range of Bitis spp. of viperid snakes upon the plasma of model species: amphibian (Cane Toad, Rhinella marina); lizard (Blue-tongue Skink, Tiliqua scincoides); avian (Domestic Chicken, Gallus gallus); and rodent (Brown Rat, Rattus norvegicus). Significant variation in coagulotoxic activity across the different plasmas was observed between species and compared to the known affects upon human plasma. Bitis caudalis was notable in being active on all four plasmas, but in extremely divergent manners: accelerating clotting times and producing strong, stable clots upon amphibian plasma (consistent with true procoagulation); accelerating clotting time but producing weak, unstable clots upon lizard plasma (consistent with pseudo-procoagulation); delaying avian clotting time beyond machine maximum reading time (strong anticoagulation consistent with either inhibition of clotting enzymes or total destruction of fibrinogen, or both); and delaying clotting of rodent plasma (consistent with inhibition of clotting enzymes) and with only weak clots formed (consistent with destruction of fibrinogen). In contrast, the sister species B. peringueyi and B. schneideri displayed activity only upon the lizard plasma, slightly accelerating the clotting times to produce weak, unstable clots (consistent with pseudo-procoagulation). The other dwarf species, B. cornuta, displayed strong anticoagulation upon avian and rodent plasmas, delaying clotting beyond the machine maximum reading time (strong anticoagulation consistent with either inhibition of clotting enzymes or total destruction of fibrinogen, or both). In contrast, the giant species studied (B. gabonica) showed only a very weak pseudo-procoagulant activity upon lizard plasma. The wide range of variation seen within this study highlights the importance of studying venom activity on relevant models when making conclusions about the ecological role of venoms and the extreme limitation in extrapolating animal results to predict potential human clinical effects.

Efficacy and Limitations of Chemically Diverse Small-Molecule Enzyme-Inhibitors against the Synergistic Coagulotoxic Activities of Bitis Viper Venoms

Snakebite remains a significant public health burden globally, disproportionately affecting low-income and impoverished regions of the world. Recently, researchers have begun to focus on the use of small-molecule inhibitors as potential candidates for the neutralisation of key snake venom toxins and as potential field therapies. Bitis vipers represent some of the most medically important as well as frequently encountered snake species in Africa, with a number of species possessing anticoagulant phospholipase A₂ (PLA₂) toxins that prevent the prothrombinase complex from inducing clot formation. Additionally, species within the genus are known to exert pseudo-procoagulant activity, whereby kallikrein enzymatic toxins cleave fibrinogen to form a weak fibrin clot that rapidly degrades, thereby depleting fibrinogen levels and contributing to the net anticoagulant state. Utilising well-validated coagulation assays measuring time until clot formation, this study addresses the in vitro efficacy of three small molecule enzyme inhibitors (marimastat, prinomastat and varespladib) in neutralising these aforementioned activities. The PLA₂ inhibitor varespladib showed the greatest efficacy for the neutralisation of PLA₂-driven anticoagulant venom activity, with the metalloproteinase inhibitors prinomastat and marimastat both showing low and highly variable degrees of cross-neutralisation with PLA₂ anticoagulant toxicity. However, none of the inhibitors showed efficacy in neutralising the pseudo-procoagulant venom activity exerted by the venom of B. caudalis. Our results highlight the complex nature of snake venoms, for which single-compound treatments will not be universally effective, but combinations might prove highly effective. Despite the limitations of these inhibitors with regards to in vitro kallikrein enzyme pseudo-procoagulant venom activity, our results further support the growing body of literature indicating the potential use of small molecule inhibitors to enhance first-aid treatment of snakebite envenoming, particularly in cases where hospital and thus antivenom treatment is either unavailable or far away.

Crotalus Durissus Ruruima: Current Knowledge on Natural History, Medical Importance, and Clinical Toxinology

Crotalus durissus ruruima is a rattlesnake subspecies mainly found in Roraima, the northernmost state of Brazil. Envenomings caused by this subspecies lead to severe clinical manifestations (e.g. respiratory muscle paralysis, rhabdomyolysis, and acute renal failure) that can lead to the victim’s death. In this review, we comprehensively describe C. d. ruruima biology and the challenges this subspecies poses for human health, including morphology, distribution, epidemiology, venom cocktail, clinical envenoming, and the current and future specific treatment of envenomings by this snake. Moreover, this review presents maps of the distribution of the snake subspecies and evidence that this species is responsible for some of the most severe envenomings in the country and causes the highest lethality rates. Finally, we also discuss the efficacy of the Brazilian horse-derived antivenoms to treat C. d. ruruima envenomings in Roraima state.

Association between Venom Immunotherapy and Changes in Serum Protein-Peptide Patterns

Venom immunotherapy (VIT) is administered to allergic patients to reduce the risk of dangerous systemic reactions following an insect sting. To better understand the mechanism of this treatment and its impact on the human organism, we analysed serum proteomic patterns obtained at five time-points from Hymenoptera-venom-allergic patients undergoing VIT. For statistical analyses, patients were additionally divided into two groups (high responders and low responders) according to serum sIgG4 levels. VIT was found to be associated with changes in seven proteins: the fibrinogen alpha chain, complement C4-A, complement C3, filamin-B, kininogen-1, myosin-9 and inter-alpha-trypsin inhibitor heavy chain H1. The number of discriminative m/z (mass-to-charge ratio) features increased up to the 90th day of VIT, which may be associated with the development of immunity after the administration of increased venom doses. It may also suggest that during VIT, there may occur processes involved not only in protein synthesis but also in protein degradation (caused by proteolytic venom components). The results are consistent with measured serum sIgG4 levels, which increased from 2.04 mgA/I at baseline to 7.25 mgA/I at 90 days. Moreover, the major proteomic changes were detected separately in the high responder group. This may suggest that changes in protein–peptide profiles reflect the actual response to VIT.

Beyond hemostasis: a snake venom serine protease with potassium channel blocking and potential antitumor activities

Snake venom serine proteases (SVSPs) are complex and multifunctional enzymes, acting primarily on hemostasis. In this work, we report the hitherto unknown inhibitory effect of a SVSP, named collinein-1, isolated from the venom of Crotalus durissus collilineatus, on a cancer-relevant voltage-gated potassium channel (hEAG1). Among 12 voltage-gated ion channels tested, collinein-1 selectively inhibited hEAG1 currents, with a mechanism independent of its enzymatic activity. Corroboratively, we demonstrated that collinein-1 reduced the viability of human breast cancer cell line MCF7 (high expression of hEAG1), but does not affect the liver carcinoma and the non-tumorigenic epithelial breast cell lines (HepG2 and MCF10A, respectively), which present low expression of hEAG1. In order to obtain both functional and structural validation of this unexpected discovery, where an unusually large ligand acts as an inhibitor of an ion channel, a recombinant and catalytically inactive mutant of collinein-1 (His43Arg) was produced and found to preserve its capability to inhibit hEAG1. A molecular docking model was proposed in which Arg79 of the SVSP 99-loop interacts directly with the potassium selectivity filter of the hEAG1 channel.

Hypotensive Snake Venom Components-A Mini-Review

Hypertension is considered a major public health issue due to its high prevalence and subsequent risk of cardiovascular and kidney diseases. Thus, the search for new antihypertensive compounds remains of great interest. Snake venoms provide an abundant source of lead molecules that affect the cardiovascular system, which makes them prominent from a pharmaceutical perspective. Such snake venom components include bradykinin potentiating peptides (proline-rich oligopeptides), natriuretic peptides, phospholipases A₂, serine-proteases and vascular endothelial growth factors. Some heparin binding hypotensive factors, three-finger toxins and 5' nucleotidases can also exert blood pressure lowering activity. Great advances have been made during the last decade regarding the understanding of the mechanism of action of these hypotensive proteins. Bradykinin potentiating peptides exert their action primarily by inhibiting the angiotensin-converting enzyme and increasing the effect of endogenous bradykinin. Snake venom phospholipases A₂ are capable of reducing blood pressure through the production of arachidonic acid, a precursor of cyclooxygenase metabolites (prostaglandins or prostacyclin). Other snake venom proteins mimic the effects of endogenous kallikrein, natriuretic peptides or vascular endothelial growth factors. The aim of this work was to review the current state of knowledge regarding snake venom components with potential antihypertensive activity and their mechanisms of action.

Functional and biological insights of rCollinein-1, a recombinant serine protease from Crotalus durissus collilineatus

Background:

The prevalent class of snake venom serine proteases (SVSP) in Viperidae venoms is the thrombin-like enzymes, which, similarly to human thrombin, convert fibrinogen into insoluble fibrin monomers. However, thrombin-like serine proteases differ from thrombin by being unable to activate factor XIII, thus leading to the formation of loose clots and fibrinogen consumption. We report the functional and biological characterization of a recombinant thrombin-like serine protease from Crotalus durissus collilineatus, named rCollinein-1.

Methods:

Heterologous expression of rCollinein-1 was performed in Pichia pastoris system according to a previously standardized protocol, with some modifications. rCollinein-1 was purified from the culture medium by a combination of three chromatographic steps. The recombinant toxin was tested in vitro for its thrombolytic activity and in mice for its edematogenicity, blood incoagulability and effect on plasma proteins.

Results:

When tested for the ability to induce mouse paw edema, rCollinein-1 demonstrated low edematogenic effect, indicating little involvement of this enzyme in the inflammatory processes resulting from ophidian accidents. The rCollinein-1 did not degrade blood clots in vitro, which suggests that this toxin lacks fibrinolytic activity and is not able to directly or indirectly activate the fibrinolytic system. The minimal dose of rCollinein-1 that turns the blood incoagulable in experimental mice is 7.5 mg/kg. The toxin also led to a significant increase in activated partial thromboplastin time at the dose of 1 mg/kg in the animals. Other parameters such as plasma fibrinogen concentration and prothrombin time were not significantly affected by treatment with rCollinein-1 at this dose. The toxin was also able to alter plasma proteins in mouse after 3 h of injection at a dose of 1 mg/kg, leading to a decrease in the intensity of beta zone and an increase in gamma zone in agarose gel electrophoresis

Conclusion:

These results suggest that the recombinant enzyme has no potential as a thrombolytic agent but can be applied in the prevention of thrombus formation in some pathological processes and as molecular tools in studies related to hemostasis.

Mechanisms underpinning the permanent muscle damage induced by snake venom metalloprotease

Snakebite is a major neglected tropical health issue that affects over 5 million people worldwide resulting in around 1.8 million envenomations and 100,000 deaths each year. Snakebite envenomation also causes innumerable morbidities, specifically loss of limbs as a result of excessive tissue/muscle damage. Snake venom metalloproteases (SVMPs) are a predominant component of viper venoms, and are involved in the degradation of basement membrane proteins (particularly collagen) surrounding the tissues around the bite site. Although their collagenolytic properties have been established, the molecular mechanisms through which SVMPs induce permanent muscle damage are poorly understood. Here, we demonstrate the purification and characterisation of an SVMP from a viper (Crotalus atrox) venom. Mass spectrometry analysis confirmed that this protein is most likely to be a group III metalloprotease (showing high similarity to VAP2A) and has been referred to as CAMP (Crotalus atrox metalloprotease). CAMP displays both collagenolytic and fibrinogenolytic activities and inhibits CRP-XL-induced platelet aggregation. To determine its effects on muscle damage, CAMP was administered into the tibialis anterior muscle of mice and its actions were compared with cardiotoxin I (a three-finger toxin) from an elapid snake (Naja pallida) venom. Extensive immunohistochemistry analyses revealed that CAMP significantly damages skeletal muscles by attacking the collagen scaffold and other important basement membrane proteins, and prevents their regeneration through disrupting the functions of satellite cells. In contrast, cardiotoxin I destroys skeletal muscle by damaging the plasma membrane, but does not impact regeneration due to its inability to affect the extracellular matrix. Overall, this study provides novel insights into the mechanisms through which SVMPs induce permanent muscle damage.

Impact of Naja nigricollis Venom on the Production of Methaemoglobin

Snakebite envenomation is an affliction currently estimated to be killing upwards of 100,000 people annually. Snakebite is associated with a diverse pathophysiology due to the magnitude of variation in venom composition that is observed worldwide. The haemolytic (i.e., lysis of red blood cells) actions of snake venoms are well documented, although the direct impact of venoms on haemoglobin is not fully understood. Here we report on the varied ability of a multitude of snake venoms to oxidise haemoglobin into methaemoglobin. Moreover, our results demonstrate that the venom of an elapid, the black necked spitting cobra, Naja nigricollis, oxidises oxyhaemoglobin (Fe²⁺) into methaemoglobin (Fe³⁺) in a time- and concentration-dependent manner that is unparalleled within the 47 viper and elapid venoms evaluated. The treatment of venom with a reducing agent, dithiothreitol (DTT) is observed to potentiate this effect at higher concentrations, and the use of denatured venom demonstrates that this effect is dependent upon the heat-sensitive proteinaceous elements of the venom. Together, our results suggest that Naja nigricollis venom appears to promote methaemoglobin production to a degree that is rare within the Elapidae family, and this activity appears to be independent of proteolytic activities of venom components on haemoglobin.

Kn-Ba: a novel serine protease isolated from Bitis arietans snake venom with fibrinogenolytic and kinin-releasing activities

Background

Bitis arietans is a venomous snake found in sub-Saharan Africa and in parts of Morocco and Saudi Arabia. The envenomation is characterized by local and systemic reactions including pain, blistering, edema and tissue damage, besides hemostatic and cardiovascular disturbances, which can cause death or permanent disabilities in its victims. However, the action mechanisms that provoke these effects remain poorly understood, especially the activities of purified venom components. Therefore, in order to elucidate the molecular mechanisms that make the Bitis arietans venom so potent and harmful to human beings, this study reports the isolation and biochemical characterization of a snake venom serine protease (SVSP).

Methods

Solubilized venom was fractionated by molecular exclusion chromatography and the proteolytic activity was determined using fluorescent substrates. The peaks that showed serine protease activity were determined by blocking the proteolytic activity with site-directed inhibitors. In sequence, the fraction of interest was submitted to another cycle of molecular exclusion chromatography. The purified serine protease was identified by mass spectrometry and characterized biochemically and immunochemically.

Results

A serine protease of 33 kDa with fibrinogen-degrading and kinin-releasing activities was isolated, described, and designated herein as Kn-Ba. The experimental Butantan Institute antivenom produced against Bitis arietans venom inhibited the Kn-Ba activity.

Conclusions

The in vitro activities of Kn-Ba can be correlated with the capacity of the venom to provoke bleeding and clotting disorders as well as hypotension, which are common symptoms presented by envenomed victims. Obtaining satisfactory Kn-Ba inhibition through the experimental antivenom is important, given the WHO’s recommendation of immunotherapy in cases of human accidents with venomous snakes.

Electronic supplementary material

The online version of this article (10.1186/s40409-018-0176-5) contains supplementary material, which is available to authorized users.

Varespladib (LY315920) Appears to Be a Potent, Broad-Spectrum, Inhibitor of Snake Venom Phospholipase A2 and a Possible Pre-Referral Treatment for Envenomation

Snakebite remains a neglected medical problem of the developing world with up to 125,000 deaths each year despite more than a century of calls to improve snakebite prevention and care. An estimated 75% of fatalities from snakebite occur outside the hospital setting. Because phospholipase A2 (PLA2) activity is an important component of venom toxicity, we sought candidate PLA2 inhibitors by directly testing drugs. Surprisingly, varespladib and its orally bioavailable prodrug, methyl-varespladib showed high-level secretory PLA2 (sPLA2) inhibition at nanomolar and picomolar concentrations against 28 medically important snake venoms from six continents. In vivo proof-of-concept studies with varespladib had striking survival benefit against lethal doses of Micrurus fulvius and Vipera berus venom, and suppressed venom-induced sPLA2 activity in rats challenged with 100% lethal doses of M. fulvius venom. Rapid development and deployment of a broad-spectrum PLA2 inhibitor alone or in combination with other small molecule inhibitors of snake toxins (e.g., metalloproteases) could fill the critical therapeutic gap spanning pre-referral and hospital setting. Lower barriers for clinical testing of safety tested, repurposed small molecule therapeutics are a potentially economical and effective path forward to fill the pre-referral gap in the setting of snakebite.

Connexin40 regulates platelet function

The presence of multiple connexins was recently demonstrated in platelets, with notable expression of Cx37. Studies with Cx37-deficient mice and connexin inhibitors established roles for hemichannels and gap junctions in platelet function. It was uncertain, however, whether Cx37 functions alone or in collaboration with other family members through heteromeric interactions in regulation of platelet function. Here we report the presence and functions of an additional platelet connexin, Cx40. Inhibition of Cx40 in human platelets or its deletion in mice reduces platelet aggregation, fibrinogen binding, granule secretion and clot retraction. The effects of the Cx37 inhibitor (37,43)Gap27 on Cx40(-/-) mouse platelets and of the Cx40 inhibitor (40)Gap27 on Cx37(-/-) mouse platelets revealed that each connexin is able to function independently. Inhibition or deletion of Cx40 reduces haemostatic responses in mice, indicating the physiological importance of this protein in platelets. We conclude that multiple connexins are involved in regulating platelet function, thereby contributing to haemostasis and thrombosis.

Sequence and phylogenetic analysis of viper venom serine proteases

Snakebites are a major neglected tropical disease responsible for as many as 95000 deaths every year worldwide. Viper venom serine proteases disrupt haemostasis of prey and victims by affecting various stages of the blood coagulation system. A better understanding of their sequence, structure, function and phylogenetic relationships will improve the knowledge on the pathological conditions and aid in the development of novel therapeutics for treating snakebites. A large dataset for all available viper venom serine proteases was developed and analysed to study various features of these enzymes. Despite the large number of venom serine protease sequences available, only a small proportion of these have been functionally characterised. Although, they share some of the common features such as a C-terminal extension, GWG motif and disulphide linkages, they vary widely between each other in features such as isoelectric points, potential N-glycosylation sites and functional characteristics. Some of the serine proteases contain substitutions for one or more of the critical residues in catalytic triad or primary specificity pockets. Phylogenetic analysis clustered all the sequences in three major groups. The sequences with substitutions in catalytic triad or specificity pocket clustered together in separate groups. Our study provides the most complete information on viper venom serine proteases to date and improves the current knowledge on the sequence, structure, function and phylogenetic relationships of these enzymes. This collective analysis of venom serine proteases will help in understanding the complexity of envenomation and potential therapeutic avenues.

Rhinocetin, a venom-derived integrin-specific antagonist inhibits collagen-induced platelet and endothelial cell functions

Snaclecs are small non-enzymatic proteins present in viper venoms reported to modulate hemostasis of victims through effects on platelets, vascular endothelial, and smooth muscle cells. In this study, we have isolated and functionally characterized a snaclec that we named "rhinocetin" from the venom of West African gaboon viper, Bitis gabonica rhinoceros. Rhinocetin was shown to comprise α and β chains with the molecular masses of 13.5 and 13 kDa, respectively. Sequence and immunoblot analysis of rhinocetin confirmed this to be a novel snaclec. Rhinocetin inhibited collagen-stimulated activation of human platelets in a dose-dependent manner but displayed no inhibitory effects on glycoprotein VI (collagen receptor) selective agonist, CRP-XL-, ADP-, or thrombin-induced platelet activation. Rhinocetin antagonized the binding of monoclonal antibodies against the α2 subunit of integrin α2β1 to platelets and coimmunoprecipitation analysis confirmed integrin α2β1 as a target for this venom protein. Rhinocetin inhibited a range of collagen-induced platelet functions such as fibrinogen binding, calcium mobilization, granule secretion, aggregation, and thrombus formation. It also inhibited integrin α2β1-dependent functions of human endothelial cells. Together, our data suggest rhinocetin to be a modulator of integrin α2β1 function and thus may provide valuable insights into the role of this integrin in physiological and pathophysiological scenarios, including hemostasis, thrombosis, and envenomation.

Evolutionary analysis of novel serine proteases in the venom gland transcriptome of Bitis gabonica rhinoceros

BACKGROUND

Serine proteases are major components of viper venom and target various stages of the blood coagulation system in victims and prey. A better understanding of the diversity of serine proteases and other enzymes present in snake venom will help to understand how the complexity of snake venom has evolved and will aid the development of novel therapeutics for treating snake bites.

METHODOLOGY AND PRINCIPAL FINDINGS

Four serine protease-encoding genes from the venom gland transcriptome of Bitis gabonica rhinoceros were amplified and sequenced. Mass spectrometry suggests the four enzymes corresponding to these genes are present in the venom of B. g. rhinoceros. Two of the enzymes, rhinocerases 2 and 3 have substitutions to two of the serine protease catalytic triad residues and are thus unlikely to be catalytically active, though they may have evolved other toxic functions. The other two enzymes, rhinocerases 4 and 5, have classical serine protease catalytic triad residues and thus are likely to be catalytically active, however they have glycine rather than the more typical aspartic acid at the base of the primary specificity pocket (position 189). Based on a detailed analysis of these sequences we suggest that alternative splicing together with individual amino acid mutations may have been involved in their evolution. Changes within amino acid segments which were previously proposed to undergo accelerated change in venom serine proteases have also been observed.

CONCLUSIONS AND SIGNIFICANCE

Our study provides further insight into the diversity of serine protease isoforms present within snake venom and discusses their possible functions and how they may have evolved. These multiple serine protease isoforms with different substrate specificities may enhance the envenomation effects and help the snake to adapt to new habitats and diets. Our findings have potential for helping the future development of improved therapeutics for snake bites.

Purification and characterization of a novel serine protease from the mushroom Pholiota nameko

A novel serine protease, with a molecular mass of 19 kDa and the N-terminal sequence of ARTPEAPAEV, was isolated from dried fruiting bodies of the mushroom Pholiota nameko. The purification protocol comprised ion exchange chromatography on DEAE-cellulose, Q-Sepharose and SP-Sepharose, and gel filtration on Superdex 75. It was unadsorbed on DEAE-cellulose and Q-Sepharose but adsorbed on SP-Sepharose. It exhibited an optimum temperature at 50°C, an optimum pH at pH 8.8, a Km of 5.64 mg/mL and a Vmax of 0.98 μmol/min/mL against substrate casein. A number of metal ions inhibited the enzyme including Pb(2+), Mn(2+), Ca(2+), Hg(2+), Zn(2+), Cu(2+), Co(2+), Fe(3+) and Al(3+), with the inhibition of the last two cations being the most potent. K(+) and Mg(2+) slightly enhanced, while Li(+) moderately potentiated the activity of the protease. The protease was strongly inhibited by phenylmethylsulfonyl fluoride (PMSF), suggesting that it is a serine protease.

Purification and functional characterisation of rhiminopeptidase A, a novel aminopeptidase from the venom of Bitis gabonica rhinoceros

Background

Snake bite is a major neglected public health issue within poor communities living in the rural areas of several countries throughout the world. An estimated 2.5 million people are bitten by snakes each year and the cost and lack of efficacy of current anti-venom therapy, together with the lack of detailed knowledge about toxic components of venom and their modes of action, and the unavailability of treatments in rural areas mean that annually there are around 125,000 deaths worldwide. In order to develop cheaper and more effective therapeutics, the toxic components of snake venom and their modes of action need to be clearly understood. One particularly poorly understood component of snake venom is aminopeptidases. These are exo-metalloproteases, which, in mammals, are involved in important physiological functions such as the maintenance of blood pressure and brain function. Although aminopeptidase activities have been reported in some snake venoms, no detailed analysis of any individual snake venom aminopeptidases has been performed so far. As is the case for mammals, snake venom aminopeptidases may also play important roles in altering the physiological functions of victims during envenomation. In order to further understand this important group of snake venom enzymes we have isolated, functionally characterised and analysed the sequence-structure relationships of an aminopeptidase from the venom of the large, highly venomous West African gaboon viper, Bitis gabonica rhinoceros.

Methodology and Principal Findings

The venom of B. g. rhinoceros was fractionated by size exclusion chromatography and fractions with aminopeptidase activities were isolated. Fractions with aminopeptidase activities showed a pure protein with a molecular weight of 150 kDa on SDS-PAGE. In the absence of calcium, this purified protein had broad aminopeptidase activities against acidic, basic and neutral amino acids but in the presence of calcium, it had only acidic aminopeptidase activity (APA). Together with the functional data, mass spectrometry analysis of the purified protein confirmed this as an aminopeptidase A and thus this has been named as rhiminopeptidase A. The complete gene sequence of rhiminopeptidase A was obtained by sequencing the PCR amplified aminopeptidase A gene from the venom gland cDNA of B. g. rhinoceros. The gene codes for a predicted protein of 955 amino acids (110 kDa), which contains the key amino acids necessary for functioning as an aminopeptidase A. A structural model of rhiminopeptidase A shows the structure to consist of 4 domains: an N-terminal saddle-shaped β domain, a mixed α and β catalytic domain, a β-sandwich domain and a C-terminal α helical domain.

Conclusions

This study describes the discovery and characterisation of a novel aminopeptidase A from the venom of B. g. rhinoceros and highlights its potential biological importance. Similar to mammalian aminopeptidases, rhiminopeptidase A might be capable of playing roles in altering the blood pressure and brain function of victims. Furthermore, it could have additional effects on the biological functions of other host proteins by cleaving their N-terminal amino acids. This study points towards the importance of complete analysis of individual components of snake venom in order to develop effective therapies for snake bites.

Snake bite is a major neglected public health issue causing an estimated 125,000 deaths each year, predominantly within poor communities living in rural areas of countries in South East Asia and Africa. Current treatments for snake bites are costly and have limited effectiveness, thus there is a need to develop novel therapeutics. In order to do this the toxic components of snake venom need to be clearly understood. Enzymes called aminopeptidases have been noticed in several snake venoms, but their functions have not been characterised. Related enzymes are also present in mammals, where they are involved in the maintenance of blood pressure and brain function. To further understand this important group of enzymes within snake venom we have purified and analysed the function and structure of an aminopeptidase from the venom of the West African gaboon viper. Our results suggest that this enzyme could also affect the maintenance of blood pressure and brain function in victims of snake bites. Along with other snake venom components, aminopeptidases might be a potential therapeutic target for developing novel treatments for snake bites.