A 28 kDa-protein with disintegrin-like structure (jararhagin-C) purified from Bothrops jararaca venom inhibits collagen- and ADP-induced platelet aggregation

Genomic Confirmation of the P-IIIe Subclass of Snake Venom Metalloproteinases and Characterisation of Its First Member, a Disintegrin-Like/Cysteine-Rich Protein

Disintegrin-like/cysteine-rich (DC) proteins have long been regarded just as products of proteolysis of P-III snake venom metalloproteinases (SVMPs). However, here we demonstrate that a DC protein from the venom of Vipera ammodytes (Vaa; nose-horned viper), VaaMPIII-3, is encoded per se by a P-III SVMP-like gene that has a deletion in the region of the catalytic metalloproteinase domain and in part of the non-catalytic disintegrin-like domain. In this way, we justify the proposal of the introduction of a new subclass P-IIIe of SVMP-derived DC proteins. We purified VaaMPIII-3 from the venom of Vaa in a series of chromatographic steps. A covalent chromatography step based on thiol-disulphide exchange revealed that VaaMPIII-3 contains an unpaired Cys residue. This was demonstrated to be Cys6 in about 90% and Cys19 in about 10% of the VaaMPIII-3 molecules. We further constructed a three-dimensional homology model of VaaMPIII-3. From this model, it is evident that both Cys6 and Cys19 can pair with Cys26, which suggests that the intramolecular thiol-disulphide exchange has a regulatory function. VaaMPIII-3 is an acidic 21-kDa monomeric glycoprotein that exists in at least six N-glycoforms, with isoelectric points ranging from pH 4.5 to 5.1. Consistent with the presence of an integrin-binding motif in its sequence, SECD, VaaMPIII-3 inhibited collagen-induced platelet aggregation. It also inhibited ADP- and arachidonic-acid-induced platelet aggregation, but not ristocetin-induced platelet agglutination and the blood coagulation cascade.

Jararhagin-C, a disintegrin-like protein, improves wound healing in mice through stimulation of M2-like macrophage, angiogenesis and collagen deposition

Jararhagin-C (Jar-C) is a disintegrin-like protein, isolated from the venom of B. jararaca, with affinity for α2β1 integrin and the ability to incite processes such as angiogenesis and collagen deposition in vivo. Thus, we raised the hypothesis that this protein could be used as a therapeutic strategy for stimulating the healing of excisional wounds in mice. Four wounds were made on the back of Swiss mice, treated with daily intradermal injections of PBS (control group) or Jar-C (200 ng). Ten animals from each experimental group were euthanized and the tissue from the wounds and skin around them were collected for further biochemical, histological and molecular analysis. Wounds treated with Jar-C showed a faster closure rate, accompanied by a reduction in neutrophil infiltrate (MPO), pro-inflammatory cytokine levels (TNF, CXCL1 and CCL2) and an accumulation of macrophages in the analyzed tissues. It was also observed a greater expression of genes associated with the phenotype of alternatively activated macrophages (M2). Concomitantly, the administration of Jar-C holds an angiogenic potential, increasing the density of blood vessels and the synthesis of pro-angiogenic cytokines (VEGF and FGF). We also observed an increase in collagen deposition, accompanied by higher levels of the pro-fibrogenic cytokine TGF-β1. Our data suggests Jar-C stimulates wound healing through stimulation of M2-like macrophage, angiogenesis and collagen deposition. Jar-C may be explored as a therapeutic strategy for wound healing, including the treatment of chronic wounds, where processes such as inflammation, angiogenesis and the deposition / remodeling of the matrix constituents are unregulated.

Leucurogin and melanoma therapy

Leucurogin is an ECD disintegrin-like protein, cloned from Bothrops leucurus venom gland. This new protein, encompassing the disintegrin region of a PIII metalloproteinase, is produced by recombinant technology and its biological and functional activity was partially characterized in this study. Biological activity was characterized in vitro using human fibroblasts. Functional activity of leucurogin was analysed in vitro and in vivo with murine B16F10 Nex-2 and human melanoma BLM cells. The results show that leucurogin inhibits cellular processes dependent on collagen type I. In a competition assay with collagen, leucurogin inhibits, in a dose-dependent manner, the adhesion of fibroblast to collagen. At 10 μM leucurogin reduces adhesion (40%) and migration (70%) of hFb and inhibits migration (32%) and proliferation (65%) of BLM cells. At 2.5 μM leucurogin inhibits 80% cell proliferation of B16F10 Nex-2 melanoma cells. At 4.8 μM leucurogin inhibits, in vitro, the vascular structures formation by endothelial cells by 66%. Leucurogin, injected intraperitoneally, i.p. (5 μg/animal, two-month old C57/Bl6 male mice) on alternate days for 15 days, inhibits lung metastasis of B16F10 Nex-2 cells by 70-75%. In the treatment of human melanoma, grafted intradermally in the nude mice flank, leucurogin (7.5 μg/kg in alternate days during 17 days) inhibits tumor growth by more than 40%. Leucurogin can be considered a promising agent for melanoma treatment.

Inflammation, angiogenesis and fibrogenesis are differentially modulated by distinct domains of the snake venom metalloproteinase jararhagin

Jararhagin, a metalloprotease from Bothrops jararaca snake venom, is a toxin containing the metalloproteinase, disintegrin-like and cysteine-rich domains; it causes acute inflammation and damage to vascular tissue. However, the actions of these domains on key components of chronic inflammation have not been determined. Our aim was to investigate the effects of jararhagin (Jar), jararhagin-C (Jar-C) and o-phenantrolin-treated jararhagin (Jar-Phe), on inflammatory response, blood vessel formation and extracellular matrix deposition in the murine sponge model. The polyether-polyurethane sponge matrix was implanted into Balb/c mice and injected daily with Jar (400 ng), Jar-Phe (400 ng), Jar-C (200 ng) or saline (control). Nine days after implantation, the sponge discs were removed and processed. In the Jar-treated implants, some of inflammatory markers (N-acetyl-β-d-glucosaminidase activity, CCL2 and TNF-α) and TGF-β1 levels were higher compared with the control group. In the Jar-C group, the inflammatory markers myeloperoxidase activity and CXCL1 were higher compared with the control. In this group, VEGF levels and collagen deposition were also higher. Jar-Phe treatment was able to inhibit the activity and/or production of MPO, CXCL1, CCL2 and TGF-β. The differential effects of these proteins in modulating the main components of fibrovascular tissue may be exploited in the management fibroproliferative diseases.

A New Platelet-Aggregation-Inhibiting Factor Isolated from Bothrops moojeni Snake Venom

This work reports the purification and functional characterization of BmooPAi, a platelet-aggregation-inhibiting factor from Bothrops moojeni snake venom. The toxin was purified by a combination of three chromatographic steps (ion-exchange on DEAE-Sephacel, molecular exclusion on Sephadex G-75, and affinity chromatography on HiTrap™ Heparin HP). BmooPAi was found to be a single-chain protein with an apparent molecular mass of 32 kDa on 14% SDS-PAGE, under reducing conditions. Sequencing of BmooPAi by Edman degradation revealed the amino acid sequence LGPDIVPPNELLEVM. The toxin was devoid of proteolytic, haemorrhagic, defibrinating, or coagulant activities and induced no significant oedema or hyperalgesia. BmooPAi showed a rather specific inhibitory effect on ristocetin-induced platelet aggregation in human platelet-rich plasma, whereas it had little or no effect on platelet aggregation induced by collagen and adenosine diphosphate. The results presented in this work suggest that BmooPAi is a toxin comprised of disintegrin-like and cysteine-rich domains, originating from autolysis/proteolysis of PIII SVMPs from B. moojeni snake venom. This toxin may be of medical interest because it is a platelet aggregation inhibitor, which could potentially be developed as a novel therapeutic agent to prevent and/or treat patients with thrombotic disorders.

Venom-based peptide therapy: insights into anti-cancer mechanism

The 5-year relative survival rate of all types of cancer has increased significantly over the past three decades partly due to the targeted therapy. However, still there are many targeted therapy drugs could play a role only in a portion of cancer patients with specific molecular alternation. It is necessary to continue to develop new biological agents which could be used alone and/or in combination with current FDA approved drugs to treat complex cancer diseases. Venom-based drugs have been used for hundreds of years in human history. Nevertheless, the venom-origin of the anti-cancer drug do rarely appear in the pharmaceutical market; and this is due to the fact that the mechanism of action for a large number of the venom drug such as venom-based peptide is not clearly understood. In this review, we focus on discussing some identified venom-based peptides and their anti-cancer mechanisms including the blockade of cancer cell proliferation, invasion, angiogenesis, and metastasis (hallmarks of cancer) to fulfill the gap which is hindering their use in cancer therapy. Furthermore, it also highlights the importance of immunotherapy based on venom peptide. Overall, this review provides readers for further understanding the mechanism of venom peptide and elaborates on the need to explore peptide-based therapeutic strategies.

BaltDC: purification, characterization and infrared spectroscopy of an antiplatelet DC protein isolated from Bothrops alternatus snake venom

Background

Snake venoms are a complex mixture of proteins, organic and inorganic compounds. Some of these proteins, enzymatic or non-enzymatic ones, are able to interact with platelet receptors, causing hemostatic disorders. The possible therapeutic potential of toxins with antiplatelet properties may arouse interest in the pharmacological areas. The present study aimed to purify and characterize an antiplatelet DC protein from Bothrops alternatus snake venom.

Methods

The protein, called BaltDC (DC protein from B. alternatus snake venom), was purified by a combination of ion-exchange chromatography on DEAE-Sephacel column and gel filtration on Sephadex G-75. The molecular mass was estimated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE). The amino acid sequence of the N-terminal region was carried out by Edman degradation method. Platelet aggregation assays were performed in human platelet-rich plasma (PRP). Infrared (IR) spectroscopy was used in order to elucidate the interactions between BaltDC and platelet membrane.

Results

BaltDC ran as a single protein band on SDS-PAGE and showed apparent molecular mass of 32 kDa under reducing or non-reducing conditions. The N-terminal region of the purified protein revealed the amino acid sequence IISPPVCGNELLEVGEECDCGTPENCQNECCDA, which showed identity with other snake venom metalloproteinases (SVMPs). BaltDC was devoid of proteolytic, hemorrhagic, defibrinating or coagulant activities, but it showed a specific inhibitory effect on platelet aggregation induced by ristocetin and epinephrine in PRP. IR analysis spectra strongly suggests that PO₃²⁻ groups, present in BaltDC, form hydrogen bonds with the PO₂⁻ groups present in the non-lipid portion of the membrane platelets.

Conclusions

BaltDC may be of medical interest since it was able to inhibit platelet aggregation.

Multiomics analysis of the giant triton snail salivary gland, a crown-of-thorns starfish predator

The giant triton snail (Charonia tritonis) is one of the few natural predators of the adult Crown-of-Thorns starfish (COTS), a corallivore that has been damaging to many reefs in the Indo-Pacific. Charonia species have large salivary glands (SGs) that are suspected to produce either a venom and/or sulphuric acid which can immobilize their prey and neutralize the intrinsic toxic properties of COTS. To date, there is little information on the types of toxins produced by tritons. In this paper, the predatory behaviour of the C. tritonis is described. Then, the C. tritonis SG, which itself is made up of an anterior lobe (AL) and posterior lobe (PL), was analyzed using an integrated transcriptomics and proteomics approach, to identify putative toxin- and feeding-related proteins. A de novo transcriptome database and in silico protein analysis predicts that ~3800 proteins have features consistent with being secreted. A gland-specific proteomics analysis confirmed the presence of numerous SG-AL and SG-PL proteins, including those with similarity to cysteine-rich venom proteins. Sulfuric acid biosynthesis enzymes were identified, specific to the SG-PL. Our analysis of the C. tritonis SG (AL and PL) has provided a deeper insight into the biomolecular toolkit used for predation and feeding by C. tritonis.

Metalloproteases Affecting Blood Coagulation, Fibrinolysis and Platelet Aggregation from Snake Venoms: Definition and Nomenclature of Interaction Sites

Snake venom metalloproteases, in addition to their contribution to the digestion of the prey, affect various physiological functions by cleaving specific proteins. They exhibit their activities through activation of zymogens of coagulation factors, and precursors of integrins or receptors. Based on their structure–function relationships and mechanism of action, we have defined classification and nomenclature of functional sites of proteases. These metalloproteases are useful as research tools and in diagnosis and treatment of various thrombotic and hemostatic conditions. They also contribute to our understanding of molecular details in the activation of specific factors involved in coagulation, platelet aggregation and matrix biology. This review provides a ready reference for metalloproteases that interfere in blood coagulation, fibrinolysis and platelet aggregation.

Natural Inhibitors of Snake Venom Metalloendopeptidases: History and Current Challenges

The research on natural snake venom metalloendopeptidase inhibitors (SVMPIs) began in the 18th century with the pioneering work of Fontana on the resistance that vipers exhibited to their own venom. During the past 40 years, SVMPIs have been isolated mainly from the sera of resistant animals, and characterized to different extents. They are acidic oligomeric glycoproteins that remain biologically active over a wide range of pH and temperature values. Based on primary structure determination, mammalian plasmatic SVMPIs are classified as members of the immunoglobulin (Ig) supergene protein family, while the one isolated from muscle belongs to the ficolin/opsonin P35 family. On the other hand, SVMPIs from snake plasma have been placed in the cystatin superfamily. These natural antitoxins constitute the first line of defense against snake venoms, inhibiting the catalytic activities of snake venom metalloendopeptidases through the establishment of high-affinity, non-covalent interactions. This review presents a historical account of the field of natural resistance, summarizing its main discoveries and current challenges, which are mostly related to the limitations that preclude three-dimensional structural determinations of these inhibitors using “gold-standard” methods; perspectives on how to circumvent such limitations are presented. Potential applications of these SVMPIs in medicine are also highlighted.

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

Snake venom metalloproteinases (SVMPs) are abundant in the venoms of vipers and rattlesnakes, playing important roles for the snake adaptation to different environments, and are related to most of the pathological effects of these venoms in human victims. The effectiveness of SVMPs is greatly due to their functional diversity, targeting important physiological proteins or receptors in different tissues and in the coagulation system. Functional diversity is often related to the genetic diversification of the snake venom. In this review, we discuss some published evidence that posit that processing and post-translational modifications are great contributors for the generation of functional diversity and for maintaining latency or inactivation of enzymes belonging to this relevant family of venom toxins.

ADAM and ADAMTS Family Proteins and Snake Venom Metalloproteinases: A Structural Overview

A disintegrin and metalloproteinase (ADAM) family proteins constitute a major class of membrane-anchored multidomain proteinases that are responsible for the shedding of cell-surface protein ectodomains, including the latent forms of growth factors, cytokines, receptors and other molecules. Snake venom metalloproteinases (SVMPs) are major components in most viper venoms. SVMPs are primarily responsible for hemorrhagic activity and may also interfere with the hemostatic system in envenomed animals. SVMPs are phylogenetically most closely related to ADAMs and, together with ADAMs and related ADAM with thrombospondin motifs (ADAMTS) family proteinases, constitute adamalysins/reprolysins or the M12B clan (MEROPS database) of metalloproteinases. Although the catalytic domain structure is topologically similar to that of other metalloproteinases such as matrix metalloproteinases, the M12B proteinases have a modular structure with multiple non-catalytic ancillary domains that are not found in other proteinases. Notably, crystallographic studies revealed that, in addition to the conserved metalloproteinase domain, M12B members share a hallmark cysteine-rich domain designated as the “ADAM_CR” domain. Despite their name, ADAMTSs lack disintegrin-like structures and instead comprise two ADAM_CR domains. This review highlights the current state of our knowledge on the three-dimensional structures of M12B proteinases, focusing on their unique domains that may collaboratively participate in directing these proteinases to specific substrates.

Disintegrins from snake venoms and their applications in cancer research and therapy

Integrins regulate diverse functions in cancer pathology and in tumor cell development and contribute to important processes such as cell shape, survival, proliferation, transcription, angiogenesis, migration, and invasion. A number of snake venom proteins have the ability to interact with integrins. Among these are the disintegrins, a family of small, non-enzymatic, and cysteine-rich proteins found in the venom of numerous snake families. The venom proteins may have a potential role in terms of novel therapeutic leads for cancer treatment. Disintegrin can target specific integrins and as such it is conceivable that they could interfere in important processes involved in carcinogenesis, tumor growth, invasion and migration. Herein we present a survey of studies involving the use of snake venom disintegrins for cancer detection and treatment. The aim of this review is to highlight the relationship of integrins with cancer and to present examples as to how certain disintegrins can detect and affect biological processes related to cancer. This in turn will illustrate the great potential of these molecules for cancer research. Furthermore, we also outline several new approaches being created to address problems commonly associated with the clinical application of peptide-based drugs such as instability, immunogenicity, and availability.

Isolation and characterization of moojenin, an acid-active, anticoagulant metalloproteinase from Bothrops moojeni venom

A fibrinogenolytic metalloproteinase from Bothrops moojeni venom, named moojenin, was purified by a combination of ion-exchange chromatography on DEAE-Sephacel and gel filtration on Sephacryl S-300. SDS-PAGE analysis indicated that moojenin consists of a single polypeptide chain and has a molecular mass about 45 kDa. Sequencing of moojenin by Edman degradation revealed the amino acid sequence LGPDIVSPPVCGNELLEVGEECDCGTPENCQNE, which showed strong identity with many other snake venom metalloproteinases (SVMPs). The enzyme cleaves the Aα-chain of fibrinogen first, followed by the Bβ-chain, and shows no effects on the γ-chain. Moojenin showed a coagulant activity on bovine plasma about 3.1 fold lower than crude venom. The fibrinogenolytic and coagulant activities of the moojenin were abolished by preincubation with EDTA, 1,10-phenanthroline and β-mercaptoethanol. Moojenin showed maximum activity at temperatures ranging from 30 to 40 °C and its optimal pH was 4.0. Its activity was completely lost at temperatures above 50 °C. Moojenin induced necrosis in liver and muscle, evidenced by morphological alterations, but did not cause histological alterations in mouse lungs, kidney or heart. Moojenin rendered the blood uncoagulatable when it was intraperitoneally administered into mice. This metalloproteinase may be of medical interest because of its anticoagulant activity.

Jararhagin, a hemorrhagic snake venom metalloproteinase from Bothrops jararaca

Jararhagin is a metalloproteinase isolated from Bothrops jararaca snake venom, which has been extensively studied. These studies showed its involvement on most of the systemic and local damaging effects of snakebite envenomings. In this review we comment on the major targets of jararhagin as the vascular endothelium, platelets and coagulation factors and also its action on other cell systems as inflammatory cells and their mediators, cancer and cell signaling. The mechanisms of jararhagin action are discussed together with structural features essential for the expression of its biological activities. The studies reviewed here denote jararhagin as a prototype for studies of snake venom metalloproteinases, bringing new insights into cellular-matrix interactions and adding for the improvement of snakebite treatment.

Leucurogin, a new recombinant disintegrin cloned from Bothrops leucurus (white-tailed-jararaca) with potent activity upon platelet aggregation and tumor growth

Disintegrins and disintegrins-like proteins are able to inhibit platelet aggregation and integrin-mediated cell adhesion. The aim of this study was to produce one disintegrin-like cloned from Bothrops leucurus venom gland and to characterize it regarding biological activity. The recombinant protein was purified by one step procedure involving anion-exchange chromatography (DEAE-cellulose) and presented a molecular mass of 10.4 kDa. The purified protein was able to inhibit platelet aggregation induced by collagen (IC₅₀ = 0.65 μM) and to inhibit growth of Ehrlich tumor implanted in mice by more than 50% after 7 days administration of 10 μg/day. No effects were observed upon adenosine 5'-diphosphate (ADP)-and arachidonic acid (AA)-induced platelet aggregation. The recombinant protein was recognized by an antibody specific for jararhagin one metalloproteinase isolated from Bothrops jararaca venom, and therefore it was named leucurogin. Anti-angiogenesis effect of leucurogin was evaluated by the sponge implant model. After 7 days administration leucurogin inhibited, in a dose dependent way, the vascularization process in the sponge. Leucurogin represents a new biotechnological tool to understand biological processes where disintegrins-like are involved and may help to characterize integrins that can be involved in development and progression of malignant cells.

Enzymatic toxins from snake venom: structural characterization and mechanism of catalysis

Snake venoms are cocktails of enzymes and non-enzymatic proteins used for both the immobilization and digestion of prey. The most common snake venom enzymes include acetylcholinesterases, l-amino acid oxidases, serine proteinases, metalloproteinases and phospholipases A(2) . Higher catalytic efficiency, thermal stability and resistance to proteolysis make these enzymes attractive models for biochemists, enzymologists and structural biologists. Here, we review the structures of these enzymes and describe their structure-based mechanisms of catalysis and inhibition. Some of the enzymes exist as protein complexes in the venom. Thus we also discuss the functional role of non-enzymatic subunits and the pharmacological effects of such protein complexes. The structures of inhibitor-enzyme complexes provide ideal platforms for the design of potent inhibitors which are useful in the development of prototypes and lead compounds with potential therapeutic applications.

Snake venom metalloproteinases: structure, function and relevance to the mammalian ADAM/ADAMTS family proteins

Metalloproteinases are among the most abundant toxins in many Viperidae venoms. Snake venom metalloproteinases (SVMPs) are the primary factors responsible for hemorrhage and may also interfere with the hemostatic system, thus facilitating loss of blood from the vasculature of the prey. SVMPs are phylogenetically most closely related to mammalian ADAM (a disintegrin and metalloproteinase) and ADAMTS (ADAM with thrombospondin type-1 motif) family of proteins and, together with them, constitute the M12B clan of metalloendopeptidases. Large SVMPs, referred to as the P-III class of SVMPs, have a modular architecture with multiple non-catalytic domains. The P-III SVMPs are characterized by higher hemorrhagic and more diverse biological activities than the P-I class of SVMPs, which only have a catalytic domain. Recent crystallographic studies of P-III SVMPs and their mammalian counterparts shed new light on structure-function properties of this class of enzymes. The present review will highlight these structures, particularly the non-catalytic ancillary domains of P-III SVMPs and ADAMs that may target the enzymes to specific substrates. This article is part of a Special Issue entitled: Proteolysis 50years after the discovery of lysosome.

Autolysis at the disintegrin domain of patagonfibrase, a metalloproteinase from Philodryas patagoniensis (Patagonia Green Racer; Dipsadidae) venom

Patagonfibrase is a 57.5-kDa hemorrhagic metalloproteinase isolated from the venom of Philodryas patagoniensis (Patagonia Green Racer), a South American rear-fanged snake. Herein we demonstrate that patagonfibrase undergoes autolysis at its pH optimum (7.5) and at 37 degrees C, primarily producing a approximately 32.6 kDa fragment composed of disintegrin-like and cysteine-rich domains, as identified by mass spectrometry and N-terminal sequencing. The autolysis site for production of this fragment is similar to that observed for metalloproteinases from front-fanged Viperidae snake venoms. In the presence of Ca(2+), patagonfibrase was only partially autolysed, giving rise mainly to one fragment of approximately 52.2 kDa. In addition, calcium markedly enhanced the azocaseinolytic activity of patagonfibrase. Our findings contribute to the understanding of the structural and mechanistic bases of this family of metalloenzymes that are widely distributed among snake venoms, demonstrating that important post-translational modifications such as proteolysis can also contribute to the diversity and complexity of proteins found in rear-fanged snake venoms.

Different regions of the class P-III snake venom metalloproteinase jararhagin are involved in binding to alpha2beta1 integrin and collagen

SVMPs are multi-domain proteolytic enzymes in which disintegrin-like and cysteine-rich domains bind to cell receptors, plasma or ECM proteins. We have recently reported that jararhagin, a P-III class SVMP, binds to collagen with high affinity through an epitope located within the Da-disintegrin sub-domain. In this study, we evaluated the binding of jararhagin to alpha(2)beta(1) integrin (collagen receptor) using monoclonal antibodies and recombinant jararhagin fragments. In solid phase assays, binding of jararhagin to alpha(2)beta(1) integrin was detectable from concentrations of 20 nM. Using recombinant fragments of jararhagin, only fragment JC76 (residues 344-421), showed a significant binding to recombinant alpha(2)beta(1) integrin. The anti-jararhagin monoclonal antibody MAJar 3 efficiently neutralised binding of jararhagin to collagen, but not to recombinant alpha(2)beta(1) integrin nor to cell-surface-exposed alpha(2)beta(1) integrin (alpha(2)-K562 transfected cells and platelets). The same antibody neutralised collagen-induced platelet aggregation. Our data suggest that jararhagin binding to collagen and alpha(2)beta(1) integrin occurs by two independent motifs, which are located on disintegrin-like and cysteine-rich domains, respectively. Moreover, toxin binding to collagen appears to be sufficient to inhibit collagen-induced platelet aggregation.

Platelet-active substances in the venom of Bothrops moojeni snake-a novel evaluation method using whole blood aggregometry

The objective of the present study was an investigation of the crude Bothrops moojeni venom, aiming at the identification of new compounds with platelet-activating or -inhibiting activity. The venom was separated by gel filtration chromatography into 18 fractions, which were tested by means of whole blood aggregometry for their activities affecting the aggregation of blood platelets. In order to eliminate interferences caused by prothrombin activators or thrombin like-enzymes, which are frequently present in snake venoms, a test method for screening protein mixtures was developed. To avoid clotting of the blood samples, the thrombin inhibitor hirudin and the synthetic inhibitor of fibrin polymerization Pefabloc FG were applied. In the present study, a platelet aggregation activator with an activity resembling thrombocytin from B. atrox was identified in one of the examined venom fractions. In addition, a platelet antagonist-most likely a disintegrin-with broad inhibitory activity against aggregation triggered by collagen, adenosine diphosphate and thrombin receptor activating peptide, was identified.

Leberagin-C, A disintegrin-like/cysteine-rich protein from Macrovipera lebetina transmediterranea venom, inhibits alphavbeta3 integrin-mediated cell adhesion

Leberagin-C, a new member of the disintegrin-like/cysteine-rich (D/C) family, was purified to homogeneity from the venom of Tunisian snake Macrovipera lebetina transmediterranea. It is a monomeric protein with a molecular mass of 25,787 Da. Its complete sequence of 205 amino acid residues was established by cDNA cloning. The leberagin-C shows many conserved sequences with other known D/C proteins, like the SECD binding sites and a pattern of 28 cysteines. It is the first purified protein from M. lebetina transmediterranea with only two disintegrin-like/cysteine-rich domains. Leberagin-C is able to inhibit platelet aggregation induced by thrombin and arachidonic acid with IC(50) of 40 and 50 nM respectively. It was also able to inhibit the adhesion of melanoma tumour cells on fibrinogen and fibronectin, by interfering with the function of alphavbeta3 and, to a lesser extent, with alphavbeta6 and alpha5beta1 integrins. To our knowledge, leberagin-C is the sole described D/C protein that does not specifically interact with the alpha2beta1 integrin. Structure-activity relationship study of leberagin-C suggested that there are some important amino acid differences with jararhagin, the most studied PIII metalloprotease from Bothrops jararaca, notably around the SECD motif in its disintegrin-like domain. Other regions implicated in leberagin-C specificities could not be excluded.

Engineering ecotin for identifying proteins with a trypsin fold

Ecotin is a bidentate, fold-specific inhibitor of mammalian serine-proteases produced by Escherichia coli. This molecule may be engineered to increase and/or change its affinity and specificity providing significant biotechnological potential. Since ecotin binds tightly to serine proteases of the trypsin fold, it may help to identify the role of these enzymes in different biological processes. In this work, we tested ecotin variants as an affinity purification reagent for identifying enzymes in samples of tumor progression and mammary gland involution. Initially, we used a commercial source of urokinase-type plasminogen activator (u-PA) that remained fully active after elution from an affinity column of the ecotin variant (M84R, M85R). We then successfully identified u-PA from more complex mixtures including lysates from a prostate cancer cell line and involuting mouse mammary glands. Interestingly, a membrane-type serine protease 1 was isolated from the Triton X-100-solubilized PC-3 cell lysates, and surprisingly, haptoglobin, a serine-protease homolog protein, was also identified in mammary gland lysates and in blood. Haptoglobin does not prevent ecotin inhibition of u-PA, but it may act as a carrier within blood when ecotin is used in vivo. Finally, this affinity purification matrix was also able to identify a thrombin-like enzyme from snake venom using an ecotin variant directed against thrombin. Overall, the ecotin variants acted as robust tools for the isolation and characterization of proteins with a trypsin fold. Thus, they may assist in the understanding of the role of these serine proteases and homologous proteins in different biological processes.

The three-dimensional structure of bothropasin, the main hemorrhagic factor from Bothrops jararaca venom: insights for a new classification of snake venom metalloprotease subgroups

Bothropasin is a 48kDa hemorrhagic PIII snake venom metalloprotease (SVMP) isolated from Bothrops jararaca, containing disintegrin/cysteine-rich adhesive domains. Here we present the crystal structure of bothropasin complexed with the inhibitor POL647. The catalytic domain consists of a scaffold of two subdomains organized similarly to those described for other SVMPs, including the zinc and calcium-binding sites. The free cysteine residue Cys189 is located within a hydrophobic core and it is not available for disulfide bonding or other interactions. There is no identifiable secondary structure for the disintegrin domain, but instead it is composed mostly of loops stabilized by seven disulfide bonds and by two calcium ions. The ECD region is in a loop and is structurally related to the RGD region of RGD disintegrins, which are derived from PII SVMPs. The ECD motif is stabilized by the Cys277-Cys310 disulfide bond (between the disintegrin and cysteine-rich domains) and by one calcium ion. The side chain of Glu276 of the ECD motif is exposed to solvent and free to make interactions. In bothropasin, the HVR (hyper-variable region) described for other PIII SVMPs in the cysteine-rich domain, presents a well-conserved sequence with respect to several other PIII members from different species. We propose that this subset be referred to as PIII-HCR (highly conserved region) SVMPs. The differences in the disintegrin-like, cysteine-rich or disintegrin-like cysteine-rich domains may be involved in selecting target binding, which in turn could generate substrate diversity or specificity for the catalytic domain.

Jararhagin, a snake venom metalloprotease-disintegrin, activates the Rac1 GTPase and stimulates neurite outgrowth in neuroblastoma cells

It has been shown previously that the snake venom metalloprotease-disintegrin jararhagin stimulates cell migration and cytoskeletal rearrangement, independently of its effects on cellular adhesion but possibly associated with the activation of small GTP-binding proteins from the Rho family [Costa, E.P., Santos, M.F., 2004. Toxicon 44(8), 861-870.] Here we show that jararhagin stimulates spreading, actin dynamics and neurite outgrowth in neuroblastoma cells, and that this effect is accompanied by the translocation of the Rac1 small GTPase to the membrane fraction, suggesting its activation. Stimulation of neurite outgrowth was observed within minutes and was dependent on the proteolytic activity of the toxin. These results suggest that jararhagin may stimulate neuronal differentiation, being a potential tool for neuronal regeneration studies.

Three-dimensional domain architecture of the ADAM family proteinases

A disintegrin and metalloproteinase (ADAM) family of proteins constitutes a major class of mammalian membrane-bound sheddases that are responsible for the processing of cell-surface-protein ectodomains, including the latent forms of growth factors, cytokines and their receptors. However, the molecular mechanism by which ADAMs recognize and process their substrates is largely unknown. Recent crystallographic studies on phylogenically related snake venom metalloproteinases (SVMPs) and mammalian ADAM with thrombospondin type-1 motif (ADAMTS) family proteins have shed light on the structure-function properties of ADAMs. This review will highlight these recent structures, particularly the non-catalytic ancillary domains, which might be important for substrate recognition.

Insights into and speculations about snake venom metalloproteinase (SVMP) synthesis, folding and disulfide bond formation and their contribution to venom complexity

As more data are generated from proteome and transcriptome analyses of snake venoms, we are gaining an appreciation of the complexity of the venoms and, to some degree, the various sources of such complexity. However, our knowledge is still far from complete. The translation of genetic information from the snake genome to the transcriptome and ultimately the proteome is only beginning to be appreciated, and will require significantly more investigation of the snake venom genomic structure prior to a complete understanding of the genesis of venom composition. Venom complexity, however, is derived not only from the venom genomic structure but also from transcriptome generation and translation and, perhaps most importantly, post-translation modification of the nascent venom proteome. In this review, we examine the snake venom metalloproteinases, some of the predominant components in viperid venoms, with regard to possible synthesis and post-translational mechanisms that contribute to venom complexity. The aim of this review is to highlight the state of our knowledge on snake venom metalloproteinase post-translational processing and to suggest testable hypotheses regarding the cellular mechanisms associated with snake venom metalloproteinase complexity in venoms.

Mapping von Willebrand factor A domain binding sites on a snake venom metalloproteinase cysteine-rich domain

The PIII class of the snake venom metalloproteinases (SVMPS) are acknowledged to be one of the major hemorrhage producing toxins in crotalid venoms. This class of SVMPS are structurally distinguished by the presence of disintegrin-like and cysteine-rich domains carboxy to the metalloproteinase domain and thus share structural homology with many of the ADAMs proteins. It has been suggested that the presence of the carboxy domain are the key structural determinants for potent hemorrhagic activity in that they may serve to target the proteinases to specific key extracellular matrix and cell surface substrates for proteolysis leading to hemorrhage production at the capillaries. Following from previous studies in our laboratory in this investigation we scanned the cysteine-rich domain of the PIII hemorrhagic SVMP jararhagin using synthetic peptides in an attempt to identify regions which could bind to von Willebrand factor (vWF), a known binding partner for jararhagin. From these studies we identified two such peptide, Jar6 and Jar7 that could support binding to vWF as well as block the recombinant cysteine-rich domain of jararhagin binding to vWF. Using the coordinates for the recently solved crystal structure of the PIII SVMP VAP1, we modeled the structure of jararhagin and attempted to dock the modeled cysteine-rich structure of that protein to the A1 domain of vWF. These studies indicated that effective protein-protein interaction between the two ligands was possible and supported the data indicating that the Jar6 peptide was involved, whereas the Jar7 peptide was observed to be sterically blocked from interaction. In summary, our studies have identified a region on the cysteine-rich domain of a PIII SVMP that interacts with vWF and based on molecular modeling could be involving in the interaction of the cysteine-rich domain of the SVMP with the A1 domain of vWF thus serving to target the toxin to the protein for subsequent proteolytic degradation.

Purification and functional characterization of AAV1, a novel P-III metalloproteinase, from Formosan Agkistrodon acutus venom

AAV1, an alkaline glycoprotein (GP), was purified from Agkistrodon acutus venom by two chromatographic steps on successive DEAE-Sephadex A-50 and Superdex 75 FPLC columns. AAV1 on SDS-PAGE under non-reducing conditions migrated as a monomeric and a polymeric forms with apparent molecular mass of 57 and 180 kDa, respectively. Upon reduction, it appeared as a single broad band with a mass of 50.3 kDa corresponding to the size of a typical P-III metalloproteinase acurhagin. The N-terminal sequence of an autoproteolytical 30 kDa-fragment of AAV1 showed a high homology to that of venom proteins with Metalloproteinase, Disintegrin-like, and Cysteine-rich (MDC) domains. Although it was devoid of cleaving activity toward gelatin, fibronectin and prothrombin, AAV1 preferentially digested the Aalpha chain of fibrinogen and followed by the Bbeta chain, leading to the inhibition of fibrinogen-induced platelet aggregation in elastase-treated human platelets. However, the proteolytic activity of AAV1 was completely inactivated by the chelating agent but not serine proteinase inhibitor. Furthermore, AAV1 could concentration-dependently inhibit platelet aggregation and suppress tyrosine phosphorylation of intracellular proteins in collagen- and convulxin-stimulated platelets, respectively. The interaction of MDC domains in AAV1 molecule with platelet GPVI was responsible for the inhibitory effect of AAV1 on collagen- and convulxin-induced platelet aggregation. Taken together, these pieces of evidence suggest that AAV1 from Formosan viper venom belongs to a new member of high-molecular mass metalloproteinase family and functions as a GPVI antagonist.

Molecular diversity of disintegrin-like domains within metalloproteinase precursors of Bothrops jararaca

Disintegrins are small peptides isolated from the venom of several snake families which act as integrin-antagonists or agonists, interacting with a variety of biological processes mediated by integrins. In this work we describe five new disintegrin-like domains within metalloproteinase precursor sequences, obtained from a Bothrops jararaca venom gland cDNA library. Among the new disintegrin-like domains, four were contained in PIII metalloproteinase precursors, with three of them presenting ECD-motifs and one presenting a new KCD-motif. Moreover, we found three disintegrin-like domains within PII metalloproteinase precursors. Two of them are similar to the already described disintegrins jarastatin and jararacin. The third molecule is unusual, presenting some typical PIII metalloproteinase characteristics but lacking the cysteine-rich domain being, thus, classified as a PII metalloproteinase. Only few reports presented molecules with these characteristics. Sequence analysis suggests that these molecules are intermediate steps between the more ancient PIII and the more recent PII metalloproteinases. We also investigated disintegrin N-terminus diversity in B. jararaca crude venom by purifying jarastatin and jararacin and analyzing them by mass spectrometry.

Characterization of a fibrinolytic enzyme (ussurenase) from Agkistrodon blomhoffii ussurensis snake venom: Insights into the effects of Ca2+ on function and structure

Fibrino(geno)lytic enzymes from snake venoms have been identified as high quality therapeutic agents for treatment of blood clots and strokes. They act on fibrinogen and fibrin, leading to defibrinogenation of blood, lysis of fibrin, and a consequent decrease in blood viscosity. In this work, a fibrinolytic enzyme (ussurenase) from China Agkistrodon blomhoffii Ussurensis snake venom, was purified to homogeneity, identified as a stable 23,367.8 Da monomeric protein, and was identified as a new kind of snake venom metalloproteinase. Ussurenase reacts optimally with fibrin clots at pH 7.5-8.3 and a temperature of 33-41 degrees C. Although many fibrinolytic enzymes are known to be zinc-dependent, measurements from inductively coupled plasma-atomic emission spectroscopy (ICP-AES) reveal that ussurenase is a Ca2+-containing protein with a molar ratio of 1:1 ([Ca2+]:[enzyme]). Ca2+ is crucial to the fibrin clot hydrolysis by ussurenase but also plays an important role in maintaining the structural integrity of the enzyme. The addition of Ca2+ to the apoenzyme induces a conformational change making the environments surrounding the Trp residues of the enzyme more hydrophobic. The presence of Ca2+ also increases the structural stability of ussurenase, so that higher concentrations of the denaturant guanidine hydrochloride are required to denature the native ussurenase compared to the apo-form. UV absorption and CD spectroscopy experiments show that Ca2+ increases the thermostability and changes the secondary structure of ussurenase. All these data suggest that Ca2+ is crucial for the correct folding and activity of ussurenase.

Contribution of mast cells and snake venom metalloproteinases to the hyperalgesia induced by Bothrops jararaca venom in rats

Bothrops jararaca venom (Bjv) is known to induce local inflammation and severe pain. Since, mast cells are able to secrete mediators involved in algesic processes, in this study we examined the putative role of these cells in the hyperalgesia triggered by Bjv in the rat paw. We noted that treatment with mast cell stabilizer sodium cromoglicate as well as with histamine and 5-hydroxytriptamine receptor antagonists meclizine and methysergide, respectively, inhibited the Bjv-induced hyperalgesia. In addition, we showed that stimulation of isolated rat peritoneal mast cells with Bjv in vitro resulted in the release of stored and neo-generated inflammatory mediators such as histamine and leukotriene C(4), respectively. Bjv-induced histamine secretion was clearly sensitive to treatment with sodium cromoglicate and sodium nedocromil. We further observed that metalloproteinase inhibitors 1,10-phenantroline and DM43 inhibited mast cell degranulation in vitro, under conditions where inhibitors of phospholipase A(2) as well as of serine- and cysteine-proteinases were inactive. Altogether, our findings indicate that mast cells seem to contribute to the hyperalgesia caused by Bjv in the rat paw, and also provide evidence that this response might be dependent on the ability of the Bjv to activate directly mast cells.

A snake venom metalloproteinase that inhibited cell proliferation and induced morphological changes of ECV304 cells

TSV-DM, a basic metalloproteinase with a molecular weight of 110kDa, was purified from Trimeresurus stejnegeri venom. TSV-DM degraded the Aalpha chain of fibrinogen more rapidly than the Bbeta chain in a dose dependent manner. The cDNA of TSV-DM encoded a polypeptide of 622 amino acid residues, which comprises a signal peptide, proprotein, metalloproteinase domain, spacer, disintegrin-like domain and cysteine-rich domain. The protein sequence deduced from cDNA was confirmed by peptide mass fingerprinting analysis. It is highly homologous to the members of subclass P-IIIb snake venom metalloproteinase, which comprises vascular apoptosis-inducing proteins. TSV-DM inhibited cell proliferation and induced cell morphologic changes transiently of ECV304 cells. However, DNA fragmentation and DNA content analysis demonstrated that this metalloproteinase could not induce ECV304 cells apoptosis.

Cloning of two novel P-III class metalloproteinases from Trimeresurus stejnegeri venom gland

Hemorrhagic toxins are widely distributed in viperid and crotalid snake venoms. Envenomation of Trimeresurus stejnegeri, a member of Crotalidae family, caused potent systemic and local hemorrhage. Up to now, there is no report on hemorrhage toxins from this venom. In this work, we cloned two cDNAs of P-III metalloproteinase precursors, designated as stejnihagin-A and stejnihagin-B, respectively, from T. stejnegeri venom gland. Both cDNAs encode an opening reading frame of 600 amino acid residues, containing a signal sequence, a proprotein domain, a metalloproteinase domain, a disintegrin-like domain and a cystetine-rich domain. Sequence analysis suggested that these two sequences shared highest similarity to the hemorrhagic toxin HR1b from T. flavoviridis. Aligning the deduced mature protein sequences of stejnihagin-A and stejnihagin-B with other snake venom metalloproteinases (SVMPs), we observed that stejnihagin-A and stejnihagin-B, together with HR1b shared the common cysteinyl residue at the position 100 in the metalloproteinase domain. In combination with the phylogenetic analysis, we presumed that stejnihagin-A, stejnihagin-B and HR1b might constitute a novel subclass of P-III SVMPs, named P-IIIc.

Characterization of a novel protein from Proatheris superciliaris venom: proatherocytin, a 34-kDa platelet receptor PAR1 agonist

Many toxins from viperid venoms have been characterised as powerful activators of platelets. Here, the venom from the East African Lowland viper, Proatheris superciliaris, was investigated for its effect on platelets and the coagulation system. Whole P. superciliaris venom stimulated platelet shape change and aggregation; however, the stimulation of platelet activation was unaffected by the structurally distinct Src family kinase inhibitors PP1 and PD0173952, suggesting that platelet activation was mediated by a G protein-coupled receptor. A platelet reactive 34-kDa protein was isolated from P. superciliaris venom which we have designated proatherocytin. This protein induced Src kinase-independent aggregation of both human and mouse platelets that was inhibited by the serine protease inhibitor AEBSF. Proatherocytin did not clot bovine or human fibrinogen, degrade fibrinogen or hydrolyse the serine protease substrate benzoyl-FVR-pNA. It activated human PAR1 on stably transfected rat kidney epithelial cells, whereas no activation of the trypsin receptor PAR2 was shown. Surprisingly, Edman degradation of proatherocytin revealed sequence identity with existing disintegrin-like domains of snake venom metalloproteinases. These results suggest that proatherocytin is a highly selective PAR1 agonist that also causes mouse platelet aggregation, probably through cleavage of PAR4.

Primary structure and antiplatelet mechanism of a snake venom metalloproteinase, acurhagin, from Agkistrodon acutus venom

Acurhagin has been characterized as a P-III hemorrhagic metalloproteinase. We herein report the complete sequence of acurhagin by molecular cloning. Analysis of the cDNA-predicted amino acid sequence encoding acurhagin precursor revealed that this mosaic Asn-linked glycoprotein possesses a multidomain structure including a proprotein, a metalloproteinase, a disintegrin-like and a cysteine-rich domains (189/205/102/114 residues), with an overall 87% identity to that of jararhagin, an integrin alpha2beta1-cleaving metalloproteinase. Acurhagin has a Ser-Glu-Cys-Asp sequence in the disintegrin-like domain instead of the typical Arg-Gly-Asp motif. In contrast to inhibiting fibrinogen-integrin alphaIIbbeta3 interaction by disintegrins, acurhagin selectively showed a dose-dependent inhibition on platelet aggregation induced by collagen, and suppression on tyrosine phosphorylation of several signaling proteins in convulxin-stimulated platelets. Although the immobilized acurhagin was shown to bind platelet GPVI and collagen in a primary structure- and steric conformation-dependent manner, respectively, the mechanism of acurhagin under short incubation is mainly through its binding to GPVI and collagen, instead of binding to alpha2beta1, or cleaving platelet membrane glycoproteins. Moreover, the molecular conformation maintained by divalent cations is required for the proteolytic activity of acurhagin toward extracellular matrix fibronectin. Taken together, these results suggest that all the three domains in mature acurhagin may cooperatively contribute to its biological function.

Jararhagin and its multiple effects on hemostasis

Jararhagin is a 52 kDa hemorrhagic P-III metalloproteinase isolated from the venom of the medically important Brazilian pit-viper Bothrops jararaca. It is a member of the reprolysin family of zinc metalloproteinases containing a catalytic metalloproteinase domain followed by a disintegrin-like and a cysteine-rich domain. The impact of jararhagin on hemostasis has been extensively studied using in vitro and in vivo model systems as well as in clinical studies. Jararhagin-induced hemorrhage is the result of the degradation of sub-endothelial matrix proteins leading to the disruption of the blood vessel endothelium, with accompanying disturbances in platelet function. The versatility of jararhagin is further demonstrated by its direct action on von Willebrand factor, the degradation of fibrinogen, by its inhibition of platelet adhesion to collagen and by its inability to be affected by the plasma inhibitor alpha(2)-macroglobulin. Collagen-induced platelet aggregation is inhibited by jararhagin though the binding of the molecule to the alpha(2) subunit I domain of the platelet surface alpha(2)beta(1) integrin (collagen receptor). Jararhagin also cleaves the beta(1) subunit of the same integrin, inhibiting platelet interaction and ultimately causing impairment of signal transduction. The effect of jararhagin on cell systems other than platelets is evaluated; in fibroblasts, jararhagin functions as a collagen-mimetic substrate and, in endothelial cells, it causes apoptosis and indirectly inhibits cell proliferation by release of angiostatin-like compounds. Jararhagin induces a strong pro-inflammatory response characterized by intense leukocyte accumulation at the site of the injection. Although hemorrhage and edema are a response to the direct effect of jararhagin, jararhagin-induced inflammation and necrosis are dependent on macrophages and key pro-inflammatory cytokines or their receptors. Some data also indicate that the toxin possesses anti-tumorgenic properties. Methods for inhibiting jararhagin are reviewed; this encompasses the use of synthetic peptides to the isolation of naturally occurring mammalian peptides and the development of toxin-specific antibodies through DNA immunisation and monoclonal antibody technologies. The availability of jararhagin makes it an important tool for research into the mechanisms of action of similar toxins, for insights into cellular interactions and for clinical investigations into the treatment of envenomings from B. jararaca.

Structure and function of snake venom toxins interacting with human von Willebrand factor

Hemostatic plug formation is a complex event mediated by platelets, subendothelial matrices and von Willebrand factor (VWF) at the vascular injury. Snake venom proteins have an excellent potency to regulate the interaction between VWF and platelet membrane receptors in vitro. Two protein families, C-type lectin-like proteins and Zn(2+)-metalloproteinases, have been found to affect platelet-VWF interaction. Botrocetin and bitiscetin from viper venom are disulfide-linked heterodimers with C-type lectin-like motif, and modulate VWF to elicit platelet glycoprotein Ib (GPIb)-binding activity via the A1 domain of VWF leading to the platelet agglutination. The crystal structures of botrocetin and bitiscetin together with complex from the VWF A1 domain indicate the following: (1) a central concave domain formed by two subunits of botrocetin or bitiscetin provides the binding site for VWF, (2) these modulators directly bind to the A1 domain of VWF in close proximity to the GPIb binding site, (3) both modulators induce no significant conformational change on the GPIb-binding site of the A1 domain but could provide a supplemental platform fitting for GPIb. These results suggest that the modulating mechanisms of these venoms are different from those performed by either antibiotic ristocetin in vitro or extremely high shear stress in vivo. Other modulator toxins include kaouthiagin and jararhagin, chimeric proteins composed of metalloproteinase, disintegrin-like and Cys-rich domains. These toxins cleave VWF and reduce its platelet agglutinating or collagen-binding activity. Kaouthiagin from cobra venom specifically cleaves between Pro708 and Asp709 in the C-terminal VWF A1 domain resulting in the decrease of the multimer structure of VWF. Recently a plasma proteinase, which specifically cleaves VWF into a smaller multimer, has been elucidated to be a reprolysin-like metalloproteinase with thrombospondin motif family (ADAMTS). This endogenous metalloproteinase (ADAMTS-13) specifically cleaves between Tyr842 and Met843 in the A2 domain of VWF regulating its physiological hemostatic activity. These VWF-binding snake venom proteins are suitable probes for basic research on platelet plug formation mediated by VWF, for subsidiary diagnostic use for von Willebrand disease or platelet disorder, and might be potently applicable to the regulation of VWF in thrombosis and hemostasis. Structural information of these venom proteins together with recombinant technology might strongly promote the construction of a new antihemostatic drug in the near future.

Primary structure of brevilysin L4, an enzymatically active fragment of a disintegrin precursor from Gloydius halys brevicaudus venom

Brevilysin L4 (L4) is a non-hemorrhagic P-I class metalloprotease (MP) isolated from Gloydius halys brevicaudus venom. Its complete amino acid sequence has been determined. L4 is a single-chain polypeptide and highly homologous to those of other snake venom MPs. A zinc-binding motif, HExxHxxGxxH, is located at residues 142-152. A characteristic feature of L4 is the presence of a spacer sequence (LRTDTVS) at the C-terminal that links metalloprotease and disintegrin domains and is usually removed by post-translational proteolysis, suggesting that L4 is expressed together with a spacer region and a disintegrin domain at the C-terminal. The nucleotide sequence of a cDNA clone encoding L4 has revealed that L4 is a disintegrin precursor and produced as a P-II class MP. The disintegrin coded after L4 sequence was brevicaudin 1, a disintegrin previously isolated from the same venom. P-II class MPs have been suspected to undergo autoproteolysis to release disintegrins. Although being P-I class MP, L4 itself autocatalytically degrades with a half-life of 30min at pH 8.5 and 37 degrees C in the absence of Ca(2+). Sequence analysis of several fragment peptides produced during the autolysis of L4 indicated that more than 40 peptide bonds were split, and the cleavages of Ser(60)-Asn(61), Thr(99)-Ala(100), and Phe(103)-Asp(104) bonds may trigger the autoproteolysis. Addition of Ca(2+) completely suppressed the cleavage of these particular bonds, resulting in a marked prevention of autoproteolysis. Thus, L4 provides a good model for the investigation of autolysis of some MPs.

Structural considerations of the snake venom metalloproteinases, key members of the M12 reprolysin family of metalloproteinases

The importance of proteinases in the pathologies associated with Viperid envenoming has long been appreciated. Over the past 40 years substantial research has clearly implicated metalloproteinases in the venom (snake venom metalloproteinases; SVMPs) as playing key roles in the development of such symptoms as hemorrhage, edema, hypotension, hypovolemia, inflammation and necrosis. In spite of this wealth of information there are still many unresolved questions pertaining to the structural basis for the various SVMPS giving rise to the diversity of activities. In this short review we will not attempt to provide an exhaustive collation of structural studies on the SVMPs; however, we will give a brief outline of the structural classification of the SVMPs; as well as relate them to the other members of the reprolysin family of metalloproteinases, the ADAMs. The information put forth in the text does not allow specific conclusions to be drawn on the structural basis for SVMP functional diversity, but it is our goal that it will allow for the development of testable hypotheses that can be experimentally pursued. What the reader will observe is that there are very interesting structural features displayed by the various SVMP classes and subclasses that provide insight into their functional characteristics.

Platelets as targets of snake venom metalloproteinases

For centuries snake venoms have been known to interfere with haemostasis and this is now known basically due either to toxins activating/inhibiting clotting factors, having effects on blood vessels or interfering with platelet function. In this short review, the interaction of one major group of toxins, the snake venom metalloproteinases, with platelets is considered. This is relevant for understanding the mechanism of haemorrhage induced by these toxins.