Snake Venom Constituents that Affect Platelet Function

Hemostatic Analysis of Simulated Gloydius ussuriensis Envenomation Using Canine Blood: A Comparison of Thromboelastography and Classical Coagulation Tests

Snake envenomation may lead to venom-induced consumptive coagulopathy (VICC), usually diagnosed by classical coagulation tests (CCTs), such as prothrombin time (PT) and activated partial thromboplastin time (aPTT). However, the results of CCTs are frequently normal in the initial stages, which may delay anti-venom treatments. Thromboelastography (TEG) is a point-of-care and real-time diagnostic tool that enables a comprehensive assessment of the coagulation process. This in vitro study aimed to determine concentration-dependent changes in canine blood caused by Gloydius ussuriensis (G. ussuriensis) envenomation using TEG and CCTs. Lyophilized G. ussuriensis venom was reconstructed using mouse intravenous lethal dose 50 (LD50iv) and serially diluted to 25% LD50iv, 50% LD50iv, and 75% LD50iv to reproduce VICC at different concentrations. Normal saline was used for the control. We compared TEG values of the reaction time (R), kinetic time (K), rate of clot formation (α-angle), maximum amplitude (MA), fibrinolysis at 30 min (LY30), and global strength of the clot (G) with those of PT, aPTT, fibrinogen, and platelet counts (PLTs). Most TEG parameters, except R and LY30, demonstrated statistically significant changes compared with the control at all concentrations. CCTs, except PLTs, revealed significant changes at ≥50% LD50iv. Thus, TEG could be a useful diagnostic strategy for early VICC and preventing treatment delay.

Structures and Functions of Snake Venom Metalloproteinases (SVMP) from Protobothrops venom Collected in Japan

Snake venom metalloproteinases (SVMP) are widely distributed among the venoms of Crotalinae and Viperidae, and are organized into three classes (P-I, P-II and P-III) according to their size and domain structure. P-I SVMP are the smallest SVMP, as they only have a metalloproteinase (M) domain. P-II SVMP contain a disintegrin-like (D) domain, which is connected by a short spacer region to the carboxyl terminus of the M domain. P-III SVMP contain a cysteine-rich (C) domain, which is attached to the carboxyl terminus of the D domain. Some SVMP exhibit hemorrhagic activity, whereas others do not. In addition, SVMP display fibrinolytic/fibrinogenolytic (FL) activity, and the physiological functions of SVMP are controlled by their structures. Furthermore, these proteinases also demonstrate fibrinogenolytic and proteolytic activity against synthetic substrates for matrix metalloproteinases and ADAM (a disintegrin and metalloproteinase). This article describes the structures and FL, hemorrhagic, and platelet aggregation-inhibiting activity of SVMP derived from Protobothrops snake venom that was collected in Japan.

Anti-thrombotic agents derived from snake venom proteins

Snake venoms affect blood coagulation and platelet function in a complex manner. However, two classes of venom proteins, snaclecs and disintegrins have been shown to specifically target receptors including GPIb, α2β1, GPVI, CLEC-2 and integrins αIIbβ3, αvβ3, α5β1 expressed on platelets, endothelial cells, phagocytes, tumor cells, thus affecting cell-matrices and cell-cell interactions. Here, we focus on disintegrins, a class of low molecular mass Arg-Gly-Asp(RGD)/Lys-Gly-Asp(KGD)-containing, cysteine-rich polypeptide derived from various viper snake venoms. This review describes the potential applications of disintegrins in field of integrin-related diseases, especially arterial thrombosis, angiogenesis, tumor progression and septic inflammation. In addition, a novel RGD-containing disintegrin TMV-7 is being developed as a safer antithrombotic agent with minimal side effects, such as thrombocytopenia and bleeding.

Isolation and biochemical characterization of a fibrinolytic proteinase from Bothrops leucurus (white-tailed jararaca) snake venom

In investigations aimed at characterizing snake venom clot-dissolving enzymes, we have purified a fibrinolytic proteinase from the venom of Bothrops leucurus (white-tailed jararaca). The proteinase was purified to homogeneity by a combination of molecular sieve chromatography on Sephacryl S-200 and ion-exchange chromatography on CM Sepharose. The enzyme called leucurolysin-a (leuc-a), is a 23 kDa metalloendopeptidase since it is inhibited by EDTA. PMSF, a specific serine proteinase inhibitor had no effect on leuc-a activity. The amino acid sequence was established by Edman degradation of overlapping peptides generated by a variety of selective cleavage procedures. Leuc-a is related in amino acid sequence to reprolysins. The protein is composed of 200 amino acid residues in a single polypeptide chain, possessing a blocked NH2-terminus and containing no carbohydrate. The proteinase showed proteolytic activity on dimethylcasein and on fibrin (specific activity=21.6 units/mg and 17.5 units/microg, respectively; crude venom=8.0 units/mg and 9.5 units/microg). Leuc-a degrades fibrin and fibrinogen by hydrolysis of the alpha chains. Moreover, the enzyme was capable of cleaving plasma fibronectin but not the basement membrane protein laminin. Leuc-a cleaved the Ala14-Leu15 and Tyr16-Leu17 bonds in oxidized insulin B chain. The pH optimum of the proteolysis of dimethylcasein by leuc-a was about pH 7.0. Antibody raised in rabbit against the purified enzyme reacted with leuc-a and with the crude venom of B. leucurus. In vitro studies revealed that leuc-a dissolves clots made either from purified fibrinogen or from whole blood, and unlike some other venom fibrinolytic metallopeptidases, leuc-a is devoid of hemorrhagic activity when injected (up to 100 microg) subcutaneously into mice.

Application of Recombinant Rhodostomin in Studying Cell Adhesion

Rhodostomin from venom of Agkistrodon rhodostoma (also called Calloselasma rhodostoma) contains 68 amino acid residues including 6 pairs of disulfide bonds and an arginine-glycine-aspartic acid (RGD) sequence at positions 49-51. It has been known as one of the strongest antagonists to platelet aggregation among the family termed disintegrin. In this review paper, in addition to introducing the characteristics of disintegrin and its related molecules, the advantages of using recombinant DNA technology to produce rhodostomin are described. The recombinant rhodostomin has been demonstrated to facilitate cell adhesion via interaction between the RGD motif of rhodostomin and integrins on the cell surface. This property allowed us to use the recombinant rhodostomin as an extracellular matrix to study cell adhesion and to distinguish attachment efficiency between two melanoma cell lines B16-F1 and B16-F10, the former is a low metastasis cell while the latter is a high metastasis cell. Furthermore, by using the recombinant rhodostomin as a substrate, osteoprogenitor-like cells are able to be selected and enriched within 3 days from rat bone marrow which contains a heterogeneous cell population. Finally, we show that the recombinant rhodostomin can be immobilized on beads and which serve as an affinity column to dissect cell-surface protein(s) binding to the RGD motif of rhodostomin.

Trimucytin, a collagen-like snake venom protein, activates platelets independent of I-domain within alpha2 subunit of alpha2beta1 integrin

Trimucytin is a powerful platelet aggregation inducer isolated from the venom of Taiwan habu snake (Trimeresurus mucrosquamatus). In this study, we found that the snake venom protein, crovidisin, which prevents collagen-platelet interaction through its high-affinity binding to collagen, inhibited competitively trimucytin-induced aggregation of washed human platelets with a pA(2) value of 6.65. The ability of trimucytin in triggering platelet aggregation was suppressed by a monoclonal antibody (A2-IIE10) raised against the alpha2 subunit of alpha2beta1 integrin (glycoprotein Ia/IIa), indicating that platelet alpha2beta1 integrin plays a central role in trimucytin's platelet reactivity. Many studies have localized the major reactive site of alpha2beta1 integrin to the I-domain of alpha2 subunit. However, Escherichia coli-produced recombinant alpha2 I-domain (GST-alpha2 fusion protein) blocking collagen-induced platelet aggregation failed to inhibit aggregation of platelets in response to trimucytin. Based on these findings, it is concluded that the platelet reactivity of trimucytin is alpha2beta1 integrin-dependent, while the I-domain present in the alpha2 subunit is not involved. This novel snake venom protein would be useful for mapping the functional domain of alpha2beta1 integrin.

Receptor-mediated endocytosis as a selection force to enrich bacteria expressing rhodostomin on their surface

Previously, we developed a TraT display system to express snake venom rhodostomin (RHO), a disintegrin, on the external surface of Escherichia coli [J Biomed Sci 6:64-70;1999]. To show a new potential use of the TraT display system, we employed a biotin labeling technique coupled with SDS-PAGE and flow cytometry analyses to further demonstrate and confirm the expression of TraT-RHO on the E. coli surface. We also showed that the expression of TraT-RHO on the cell surface not only facilitated the bacteria adhesion to BHK-21 cells but also induced bacterial internalization into BHK-21 cells. This feature allowed us to enrich the TraT-RHO expression bacteria about 10,000-fold starting with a mixture of TraT-RHO bacteria with beta-galactosidase-positive bacteria in a ratio of 10(2):10(7) through four cycles of BHK-21 cell endocytosis and replating of engulfed bacteria on agar plates. We therefore suggest that the TraT display system can be applied to select out bacteria expressing a specific peptide sequence from a large population of display library through the process of receptor-mediated endocytosis and reamplification cycles.

Molecular cloning and sequence analysis of aggretin, a collagen-like platelet aggregation inducer

A cDNA library derived from the Malayan-pit-viper (Calloselasma rhodostoma) venom gland was constructed in the phagemid vector. Using the information of the N-terminal amino acid sequences of two subunits of aggretin, synthetic mixed-base oligonucleotides were employed as a screening probe for colony hybridization. Separate cDNA clones encoding for the alpha and beta chains of aggretin were isolated and sequenced. The results revealed that mature alpha and beta chains contain 136 and 123 amino acid residues, respectively. Aggretin subunits show high degrees of identity with respective subunits (50-60% for alpha, 49-58% for beta) of C-type lectin-like snake venoms. The identity to rattlesnake lectin is relatively lower (i.e., 39 and 30%). All cysteine residues in each chain of aggretin are well conserved and located at the positions corresponding to those of C-type lectins. Thus, three intracatenary disulfide bridges and an interchain disulfide bond between Cys83(alpha) and Cys75(beta) may be allocated. This is the first report regarding the entire sequence of venom GPIa/IIa agonist. According to the alignment of amino acid sequences, hypervariable regions among these C-type lectin-like proteins were revealed. These hypervariable regions are proposed to be the counterparts directly interacting with different receptors or different domains of a receptor on the surface of platelet.

Recombinant rhodostomin substrates induce transformation and active calcium oscillation in human platelets

Platelet activation has been a focus of numerous studies in normal and abnormal states. Morphological changes and calcium signals found with activated platelets in vitro have been well characterized. However, the rate of cell spreading on substrates and the frequency of calcium oscillation within individual platelets upon activation have not yet been reported. In this study, we first examined the ability of a recombinant fusion protein of rhodostomin (GST-rhodostomin), a snake disintegrin containing an Arg-Gly-Asp (RGD) motif, to activate platelets when GST-rhodostomin served as a substrate. Four aspects of platelet activities induced by immobilized GST-rhodostomin and fibrinogen were analyzed in parallel. Examinations of (1) translocation of P-selectin from intracellular compartments to the plasma membrane, (2) platelet adhesion to and spreading on substrates, (3) platelet contact pattern on substrates, and (4) the degree of phosphorylation of focal adhesion kinase in platelets indicated that GST-rhodostomin was a better substrate for platelet activation than fibrinogen. Analysis of the rate of platelet spreading on GST-rhodostomin was examined by time-lapsed video microscopy. The spreading rate averaged 0.43 micrometer/minute, while cell spreading averaged 0.22 micrometer/minute when platelets were plated on fibrinogen and treated with thrombin. A newly developed method, using time-lapsed microscopy and the Metamorph program, was used to analyze calcium signals within platelets. We found that platelets on GST-rhodostomin evoked calcium oscillation at a frequency of 4.77 spike/cell/minute vs 2.76 spike/cell/minute on fibrinogen. The results of cell spreading and calcium oscillation were consistent with the results of microscopic and biochemical assays. We therefore conclude that the determination of the rate of platelet spreading and the frequency of calcium oscillation within platelets performed in this study provides more quantitative parameters for measuring platelet activities. Our results also suggest that GST-rhodostomin might potentially be used as a probe to dissect the molecular mechanisms underlying the kinetic processes of platelet activation.

A new short chain RGD-containing disintegrin, accutin, inhibits the common pathway of human platelet aggregation

A new short-chain disintegrin, accutin, was purified from the Formosan Agkistrodon acutus venom by using of gel filtration, ion exchanger and reverse phase HPLC. The homogeneous protein is a 47-residue polypeptide with a molecular mass of 5241 Da containing an Arg-Gly-Asp sequence and seven cysteinyl residues at positions highly homologous to other disintegrins. Accutin dose-dependently inhibited human platelet aggregation stimulated by ADP, collagen, thrombin or the thromboxane analogue U46619 in platelet suspension with IC50 values of 66-267 nM. It was also active in inhibiting platelet aggregation of platelet-rich plasma. However, accutin apparently did not affect the shape change caused by these agonists. Accutin also inhibited fibrinogen-induced aggregation of human elastase-treated platelets in a dose-dependent manner. Furthermore, accutin dose-dependently inhibited the binding reaction of fluorescein isothiocyanate (FITC)-conjugated arietin, a member of the disintegrin family, to human platelets. In addition, the binding of FITC-conjugated accutin to platelets was almost completely blocked by a monoclonal antibody, 7E3, raised against the platelet glycoprotein IIb/IIIa complex. On the other hand, accutin as well as other disintegrins, rhodostomin and arietin, exhibited an inhibitory effect on 7E3 binding toward platelets and endothelial cells in a dose-dependent manner. It is concluded that accutin, a new platelet aggregation inhibitor belonging to the short-chain disintegrin family, acts specifically on a binding epitope of GPIIb/IIIa overlapping with that of 7E3, leading to the blockade of fibrinogen binding to its receptor.

Full-spreading platelets induced by the recombinant rhodostomin are via binding to integrins and correlated with FAK phosphorylation

We have previously reported that non-activated platelets can be induced by morphological changes from the recombinant fusion protein of GST-rhodostomin [GST-RHO(RGD)], a member of disintegrin with an arginine-glycine-aspartic acid (RGD) motif. In this study, we further characterized the factors involved in platelet shape changes induced by rhodostomin. From less to full-spreading, four cell spreading indexes, p1, p2, s1 and s2, were designated to the platelet shape based on the scanning electron micrographs. Results of peptide competition and antibody blocking confirmed that interaction between the RGD of rhodostomin and the alpha(IIb)beta3 integrins of platelets was required for induction of a higher percentage of s2 cells. When platelets were pretreated with calphostin C, herbimycin A and cytochalasin B, respectively, the percentage of p1 and p2 cells on rhodostomin-coated plates was increased and, concomitantly, the percentage of s1 and s2 cells was decreased. Biochemical analyses indicated that the focal adhesion kinase (FAK or pp125FAK) in platelets that adhered to GST-RHO(RGD) was phosphorylated in contrast to little or no phosphorylation of FAK in cells adhered to fibrinogen or non-activated cells. Furthermore, the degree of FAK phosphorylation was consistently correlated with morphological changes in platelets treated with various drugs. Taking all the results together, we suggested that rhodostomin could directly bind to integrins of platelets and then trigger signal transduction leading to FAK phosphorylation and actin polymerization and finally resulting in platelet full-spreading.

Function of disintegrin-like/cysteine-rich domains of atrolysin A. Inhibition of platelet aggregation by recombinant protein and peptide antagonists

Snake venom hemorrhagic metalloproteinase toxins that have metalloproteinase, disintegrin-like and cysteine-rich domains are significantly more potent than toxins with only a metalloproteinase domain. The disintegrin-like domains of these toxins differ from the disintegrin peptides found in crotalid and viperid venoms by the nature of their different disulfide bond structure and, in lieu of the disintegrins' signature Arg-Gly-Asp (RGD) integrin binding sequence, there is an XXCD disulfide-bonded cysteinyl sequence in that region. Due to these apparent differences, the contribution to the overall function of the hemorrhagic metalloproteinases by the disintegrin-like domain has been unknown. In this investigation we have expressed in insect cells the disintegrin-like/cysteine-rich (DC) domains of the Crotalus atrox hemorrhagic metalloproteinase atrolysin A and demonstrated that the recombinant protein (A/DC) can inhibit collagen- and ADP-stimulated platelet aggregation. Using synthetic peptides, we have evidence that the region of the disintegrin-like domain that is positionally analogous to the RGD loop of the disintegrins is the site responsible for inhibition of platelet aggregation. For these synthetic peptides to have significant inhibitory activity, the -RSECD- cysteinyl residue must be constrained by participation in a disulfide bond with another cysteinyl residue. The two acidic amino acids adjacent to the middle cysteinyl residue in these peptides are also important for biological activity. These studies emphasize a functional role for the disintegrin-like domain in toxins and suggest structural possibilities for the design of antagonists of platelet aggregation.

Glutathione S-transferase-rhodostomin fusion protein inhibits platelet aggregation and induces platelet shape change

Rhodostomin (RHO) from Agkistrodon rhodostoma venom, consisting of 68 amino acids with an arginine-glycine-aspartic acid (RGD) sequence and 12 cysteine residues, is a potent inhibitor of platelet aggregation. We previously demonstrated that cell culture plates coated with the bacterially produced fusion protein of glutathione S-transferase-RHO [GST-RHO(RGD)] can facilitate human hepatoma cell attachment via intergrin interaction within 15 min. In this study, we further characterized the effect of RHO fusion protein on platelet cells by creating two other related fusion proteins, GST-RHO(RGE) and GST-(PS)RHO. The former was a single amino acid-substituted mutant, in which the aspartic acid residue of RGD was replaced by glutamic acid, and the latter was an insertion mutant, in which a pentapeptide of protein kinase A phosphorylation site was inserted between GST and RHO. These two mutant proteins together with a wild-type of GST-RHO(RGD) and native form of RHO were used to study effects on the inhibition of ADP-induced platelet aggregation. Results indicated that GST-RHO(RGD) inhibited platelet aggregation as potently as the native RHO, while the two other mutants were inactive. Furthermore, when unactivated platelet cells attached on the GST-RHO(RGD)-coated plate, they became a flattened pancake shape. From the results of facilitation of cell attachment on fusion protein-coated plates, we concluded that: (1) the GST-RHO(RGD) fusion protein is equally functional in inhibition of platelet aggregation and facilitation of cell attachment, which is through the interaction of RGD and integrins on the cell membrane; (2) the GST-RHO(RGE) mutant protein is unable to bind with integrins and results in loss of function; (3) the insertion mutant of GST-(PS)RHO may disrupt a proper conformation of RHO and also results in loss of function; (4) the bacterially produced fusion protein GST-RHO(RGD) can be properly used as an antithrombotic agent and an extracellular matrix.

Isolation of a venom factor devoid of proteolytic activity from Taiwan habu (Trimeresurus mucrosquamatus): N-terminal sequence homology and no functional similarity to factors IX/X-binding proteins and botrocetin

One novel venom factor was isolated and purified from the venom of Taiwan habu (Trimeresurus mucrosquamatus) using two consecutive anion-exchange and gel-filtration chromatographies followed by cation-exchange HPLC. Further characterization of the purified protein indicated that it lacks the proteolytic activity toward fibrinogen molecules, suggesting that this protein factor does not belong to the familes of metalloproteinases and thrombin-like serine proteases commonly found in the crude venoms of various crotalid snakes. The purified protein exists as a native dimeric protein of 26 kDa, consisting of two closely similar subunits of 16 and 13 kDa, held together by disulfide linkage. N-Terminal sequence analysis revealed that both chains are homologous to each other at the N-terminal fragment and also similar to the factors IX/X-binding protein isolated from Trimeresurus flavoviridis and botrocetin from Bothrops jararaca. This study points to the existence of one new two-chain venom factor without fibrinogenase activity from Taiwan habu, which, in contrast to botrocetin, promotes platelet agglutination even in the absence of von Willebrand factor. Unlike factors IX/X-binding proteins, it did not show affinity to coagulation factors IX and X in the presence of Ca2+ ion. It also shows no inhibition on thrombin, in contrast with bothrojaracin, a thrombin inhibitor isolated from Bothrops jararaca venom. We have therefore named this novel venom factor trimecetin to distinguish it from some structurally related venom factors present in various crotalid and viperid snakes.

Characterization of a cDNA encoding the precursor of platelet aggregation inhibition and metalloproteinase from Trimeresurus mucrosquamatus venom

This paper presents the nucleotide sequence of a cDNA encoding a full-length precursor of a novel platelet aggregation inhibitor named trimucrin and a hemorrhagic metalloproteinase from Trimeresurus mucrosquamatus snake venom. The deduced structure of the precursor protein is compared with those of other members of the metalloproteinase/disintegrin family.

Ex-vivo and in-vivo antithrombotic effect of triflavin, an RGD-containing peptide

Triflavin, an Arg-Gly-Asp-containing snake venom peptide, inhibits platelet aggregation through the blockade of fibrinogen binding to the activated platelets. It binds to fibrinogen receptors associated with the glycoprotein IIb/IIIa complex with a Kd value of 7 x 10(-8) M. In this study, we found that 125I-triflavin reached the maximal binding to human platelets within 5 min at 25 degrees C. In addition, when triflavin was intravenously administered at 1.0 mg kg-1 to rabbits, it reversibly impaired the platelet aggregation of platelet-rich plasma caused by ADP (20 microM) ex-vivo over 30 min. The platelet counts of the experimental rabbits remained unchanged. Triflavin was effective in reducing the mortality of ADP-induced acute pulmonary thromboembolism in mice when administered intravenously at a dose of 2 micrograms g-1. Therefore, triflavin was proven to be an effective antithrombotic agent in preventing ADP-induced acute pulmonary thromboembolism in mice and impairing reversibly the platelet function of rabbits when given intravenously.

Structural and functional aspects of RGD-containing protein antagonists of glycoprotein IIb-IIIa

In the past few years, knowledge of the structure and function of RGD-containing protein antagonists of the platelet fibrinogen receptor glycoprotein IIb-IIIa has advanced rapidly. The RGD sequence is found at the apex of extended, solvent accessible, and conformationally flexible loops in proteins of vastly different structural frameworks. Conformation of the RGD epitope and the immediate surrounding sequence are critical factors affecting potency and selectivity as integrin antagonists. The RGD sequence has recently been introduced into a number of protein and peptide scaffolds.

Triflavin, an RGD-containing antiplatelet peptide, binds to GpIIIa of ADP-stimulated platelets

Triflavin, an Arg-Gly-Asp-containing snake venom peptide, inhibits platelet aggregation through the blockade of fibrinogen binding to the activated platelets. It binds to fibrinogen receptors associated with the glycoprotein IIb/IIIa complex with a Kd value of 7 x 10(-8) M. In this report, a chemical cross-linking approach was used to further characterize the binding components of triflavin on platelet membrane. 125I-triflavin binding was performed with the aid of a chemical cross-linking reagent, DTSSP. Analysis of the cross-linked products by SDS-PAGE (7.5% gel) and subsequent autoradiogram revealed that 125I-triflavin was cross-linked specifically to a protein with an apparent molecular weight of 1.1 x 10(5), and this reaction was inhibited by GRGDS and excess of non-labeled triflavin. This 110 KDa component was identified to be GpIIIa, recognized by AP3, a mAb against GpIIIa, by immunoblotting technique. These results indicate that the triflavin-binding sites on platelets reside at a site in close proximity to GpIIIa.

An antiplatelet peptide, gabonin, from Bitis gabonica snake venom

Interaction of fibrinogen with its receptors (glycoprotein IIb/IIIa complex) on platelet membranes leads to platelet aggregation. By means of gel filtration, CM-Sephadex C-50, and reverse-phase HPLC, an antiplatelet peptide, gabonin, was purified from the venom of Bitis gabonica. The purified protein migrates as a 21,100-Da polypeptide on sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions and as a 11,000-Da peptide in the presence of beta-mercaptoethanol, indicating that gabonin is a disulfide-linked dimer. It is a polypeptide consisting of about 84 amino acid residues, rich in Asp, Pro, and half-cystine. Gabonin dose-dependently inhibited human platelet aggregation stimulated by ADP, collagen, U46619, or thrombin in preparations of platelet-rich plasma and platelet suspension (IC50 = 340-1600 nM). It also blocked platelet aggregation of whole blood. However, it apparently did not affect the initial shape change and only slightly reduced ATP release caused by aggregation agonists. Gabonin did not inhibit the rise of cytosolic calcium in Quin-2-loaded platelets stimulated by thrombin. In addition, gabonin dose-dependently inhibited fibrinogen-induced aggregation of elastase-treated platelets. In conclusion, gabonin inhibits platelet aggregation mainly through the blockade of fibrinogen binding toward fibrinogen receptors of the activated platelets.

Characterization of a protease with alpha- and beta-fibrinogenase activity from the Western diamondback rattlesnake, Crotalus atrox

A metalloprotease from the rattlesnake Crotalus atrox venom was isolated and purified from multiple-step chromatographies including anion-exchange chromatography, gel permeation and reversed-phase HPLC. The fraction was shown to be homogeneous as judged by SDS-gel electrophoresis. It also showed a high proteolytic activity against alpha- and beta-chains of fibrinogen molecules. Further characterization of the purified fraction with fibrinogenase activity indicated that it is a single-chain protease with a molecular mass of about 24 kDa and an acidic isoelectric point. It is relatively heat stable up to about 65 degrees C, inhibited by EDTA, beta-mercaptoethanol, but not by phenylmethanesulfonyl fluoride, N alpha-p-tosyl-L-phenylalanine chloromethyl ketone and N alpha-p-tosyl-L-lysine chloromethyl ketone, soybean trypsin inhibitor and aprotinin. Amino acid analysis showed that the enzyme possesses an amino acid composition very similar to some metalloproteases characterized before from the closely related rattlesnake venoms. N-Terminal sequence analysis of the enzyme corroborated some similarity between this enzyme and the reported sequences of these enzymes characterized from the Crotalidae snake family. This study indicated the presence of a novel fibrinogenase (termed Catroxase) with N-terminal sequence different from the metalloprotease with hemorrhagic activity isolated from the same Western diamondback rattlesnake.