MALDI-TOF mass spectrometry analysis of substrate specificity of lebetase, a direct-acting fibrinolytic metalloproteinase from Vipera lebetina snake venom

Post-Proline Cleaving Enzymes (PPCEs): Classification, Structure, Molecular Properties, and Applications

Proteases or peptidases are hydrolases that catalyze the breakdown of polypeptide chains into smaller peptide subunits. Proteases exist in all life forms, including archaea, bacteria, protozoa, insects, animals, and plants due to their vital functions in cellular processing and regulation. There are several classes of proteases in the MEROPS database based on their catalytic mechanisms. This review focuses on post-proline cleaving enzymes (PPCEs) from different peptidase families, as well as prolyl endoprotease/oligopeptidase (PEP/POP) from the serine peptidase family. To date, most PPCEs studied are of microbial and animal origins. Recently, there have been reports of plant PPCEs. The most common PEP/POP are members of the S9 family that comprise two conserved domains. The substrate-limiting β-propeller domain prevents unwanted digestion, while the α/β hydrolase catalyzes the reaction at the carboxyl-terminal of proline residues. PPCEs display preferences towards the Pro-X bonds for hydrolysis. This level of selectivity is substantial and has benefited the brewing industry, therapeutics for celiac disease by targeting proline-rich substrates, drug targets for human diseases, and proteomics analysis. Protein engineering via mutagenesis has been performed to improve heat resistance, pepsin-resistant capability, specificity, and protein turnover of PPCEs for pharmacological applications. This review aims to synthesize recent structure-function studies of PPCEs from different families of peptidases to provide insights into the molecular mechanism of prolyl cleaving activity. Despite the non-exhaustive list of PPCEs, this is the first comprehensive review to cover the biochemical properties, biological functions, and biotechnological applications of PPCEs from the diverse taxa.

Protease Activity Profiling of Snake Venoms Using High-Throughput Peptide Screening

Snake venom metalloproteinases (SVMPs) and snake venom serine proteinases (SVSPs) are among the most abundant enzymes in many snake venoms, particularly among viperids. These proteinases are responsible for some of the clinical manifestations classically seen in viperid envenomings, including hemorrhage, necrosis, and coagulopathies. The objective of this study was to investigate the enzymatic activities of these proteins using a high-throughput peptide library to screen for the proteinase targets of the venoms of five viperid (Echis carinatus, Bothrops asper, Daboia russelii, Bitis arietans, Bitis gabonica) and one elapid (Naja nigricollis) species of high medical importance. The proteinase activities of these venoms were each tested against 360 peptide substrates, yielding 2160 activity profiles. A nonlinear regression model that accurately described the observed enzymatic activities was fitted to the experimental data, allowing for the comparison of cleavage rates across species. In this study, previously unknown protein targets of snake venom proteinases were identified, potentially implicating novel human and animal proteins that may be involved in the pathophysiology of viper envenomings. The functional relevance of these targets was further evaluated and discussed. These new findings may contribute to our understanding of the clinical manifestations and underlying biochemical mechanisms of snakebite envenoming by viperid species.

A novel fibrinolytic metalloproteinase, barnettlysin-I from Bothrops barnetti (Barnett´s pitviper) snake venom with anti-platelet properties

BACKGROUND

Viperid snake venoms contain active components that interfere with hemostasis. We report a new P-I class snake venom metalloproteinase (SVMP), barnettlysin-I (Bar-I), isolated from the venom of Bothrops barnetti and evaluated its fibrinolytic and antithrombotic potential.

METHODS

Bar-I was purified using a combination of molecular exclusion and cation-exchange chromatographies. We describe some biochemical features of Bar-I associated with its effects on hemostasis and platelet function.

RESULTS

Bar-I is a 23.386 kDa single-chain polypeptide with pI of 6.7. Its sequence (202 residues) shows high homology to other members of the SVMPs. The enzymatic activity on dimethylcasein (DMC) is inhibited by metalloproteinase inhibitors e.g. EDTA, and by α2-macroglobulin. Bar-I degrades fibrin and fibrinogen dose- and time-dependently by cleaving their α-chains. Furthermore, it hydrolyses plasma fibronectin but not laminin nor collagen type I. In vitro Bar-I dissolves fibrin clots made either from purified fibrinogen or from whole blood. In contrast to many other P-I SVMPs, Bar-I is devoid of hemorrhagic activity. Also, Bar-I dose- and time-dependently inhibits aggregation of washed human platelets induced by vWF plus ristocetin and collagen (IC50=1.3 and 3.2 μM, respectively), presumably Bar-I cleaves both vWF and GPIb. Thus, it effectively inhibits vWF-induced platelet aggregation. Moreover, this proteinase cleaves the collagen-binding α2-A domain (160 kDa) of α2β1-integrin. This explains why it additionally inhibits collagen-induced platelet activation.

CONCLUSION

A non-hemorrhagic but fibrinolytic metalloproteinase dissolves fibrin clots in vitro and impairs platelet function.

GENERAL SIGNIFICANCE

This study provides new opportunities for drug development of a fibrinolytic agent with antithrombotic effect.

5'-Nucleotidase from Vipera lebetina venom

5'-Nucleotidase (5'-NT) is widely represented in animal tissues (CD73) as well as in almost all snake venoms. In the present study, a 5'-NT isoform has been isolated from Vipera lebetina venom. The homodimeric isoform consists of monomers with molecular masses of 60 kDa. The enzyme is thermolabile and has pH optimum at 7.5. The 5'-NT activity is inhibited by metal ions Fe(3+), Cu(2+) and Zn(2+), enhanced by Mn(2+) while Mg(2+) and Ca(2+) have no remarkable effect. In addition to 120-kDa protein there are higher molecular forms of 5'-NT present in the V. lebetina venom. The cloning and sequencing of the 5'-NT coding cDNA resulted in 5'-truncated construct. MALDI-TOF and Orbitrap mass-spectrometry of the tryptic peptides confirmed the translated N-terminally truncated protein sequence concordance to the 5'-NT isolated from the venom. The isolated protein strongly inhibited ADP- or collagen-induced platelet aggregation.

Phosphodiesterase from Vipera lebetina venom - structure and characterization

Nucleases and phosphatases are ubiquitous but mostly marginal components of snake venoms. These proteins have been studied quite extensively but up to now no data regarding their amino acid sequences confirmed at protein level have been published. The present study deals with purification, characterization, and structural properties of a phosphodiesterase from Vipera lebetina venom (VLPDE). The VLPDE with molecular mass of about 120 kDa hydrolyses ADP but not ATP and 5'-AMP. The aggregation of platelets induced by ADP or collagen is dose-dependently inhibited by VLPDE. The cloning and sequencing of the VLPDE-encoding cDNA resulted in 2772-nt sequence with ORF of 2556 nt. The translated sequence comprises 851 amino acids including the 23-amino acid signal peptide. VLPDE is synthesized as a 828-amino acid single-chain protein but subsequently cleaved to form a two-chain protein held together with disulfide bonds. In reducing conditions the enzyme behaves like a heterodimeric protein but, differently from the real heterodimers, it is synthesized as a single-chain protein. VLPDE is the first snake venom phosphodiesterase with established and confirmed primary structure.

Purification and biochemical characterization of a fibrin(ogen)olytic metalloprotease from Macrovipera mauritanica snake venom which induces vascular permeability

In the present study, a novel fibrin(ogen)olytic metalloprotease from Macrovipera mauritanica snake venom was purified and characterized in terms of enzyme kinetics and substrate specificity. The purified enzyme [termed snake venom metalloprotease-Macrovipera mauritanica (SVMP‑MM)] was composed of a single polypeptide with an apparent molecular weight of 27 kDa, as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The N-terminus of the enzyme was composed of NH(2)-QRFAPRYIEL-COOH, as determined by N-terminal sequencing. The Aα- and the Bβ-chains of fibrinogen were completely cleaved by SVMP-MM within 20 and 480 min, respectively. However, the γ-chain was much more resistant to digestion by the enzyme. The enzyme also exhibited proteolytic activity, cleaving the α-α polymer of cross-linked fibrin, but did not effectively digest the γ-γ polymer. To determine the kinetic parameters for SVMP-MM, a fluorescence-quenching peptide (termed o-aminobenzoic acid-HTEKLVTS-2,4-dinitrophenyl‑NH(2)) containing a K-L sequence for SVMP-MM cleavage was designed and synthesized. The optimal pH and temperature for the enzyme activity were found to be 5.5 and 37˚C, respectively, when the fluorogenic substrate was synthesized and used as a substrate. Among the various divalent cations tested, Ni(2+) and Cu(2+) showed strong inhibitory effects on enzyme activity, with an average of 69.6% inhibition. The enzyme activity was also inhibited by treatment with 1,10-phenanthroline, ethylenediaminetetraacetic acid and glycol-bis-(2‑aminoethylether)-N,N,N',N'-tetra-acetic acid, but not with aprotinin, tosyl-lysine chloromethyl ketone and tosyl-phenylalanyl chloromethyl ketone, suggesting that SVMP-MM is a metalloprotease and not a serine protease. The enzymatic parameters, including the K(M), k(cat), and k(cat)/K(M) values were estimated to be 0.015 mM, 0.031 sec(-1), and 20.67 mM(-1)sec(-1), respectively. SVMP-MM induced vascular permeability by digesting type IV collagen. The results obtained in our study demonstrate that SVMP-MM is a fibrin(ogen)olytic P-I class metalloprotease, which can induce a hemorrhagic reaction in vivo.

Peptidomics of three Bothrops snake venoms: insights into the molecular diversification of proteomes and peptidomes

Snake venom proteomes/peptidomes are highly complex and maintenance of their integrity within the gland lumen is crucial for the expression of toxin activities. There has been considerable progress in the field of venom proteomics, however, peptidomics does not progress as fast, because of the lack of comprehensive venom sequence databases for analysis of MS data. Therefore, in many cases venom peptides have to be sequenced manually by MS/MS analysis or Edman degradation. This is critical for rare snake species, as is the case of Bothrops cotiara (BC) and B. fonsecai (BF), which are regarded as near threatened with extinction. In this study we conducted a comprehensive analysis of the venom peptidomes of BC, BF, and B. jararaca (BJ) using a combination of solid-phase extraction and reversed-phase HPLC to fractionate the peptides, followed by nano-liquid chromatography-tandem MS (LC-MS/MS) or direct infusion electrospray ionization-(ESI)-MS/MS or MALDI-MS/MS analyses. We detected marked differences in the venom peptidomes and identified peptides ranging from 7 to 39 residues in length by de novo sequencing. Forty-four unique sequences were manually identified, out of which 30 are new peptides, including 17 bradykinin-potentiating peptides, three poly-histidine-poly-glycine peptides and interestingly, 10 L-amino acid oxidase fragments. Some of the new bradykinin-potentiating peptides display significant bradykinin potentiating activity. Automated database search revealed fragments from several toxins in the peptidomes, mainly from l-amino acid oxidase, and allowed the determination of the peptide bond specificity of proteinases and amino acid occurrences for the P4-P4' sites. We also demonstrate that the venom lyophilization/resolubilization process greatly increases the complexity of the peptidome because of the imbalance caused to the venom proteome and the consequent activity of proteinases on venom components. The use of proteinase inhibitors clearly showed different outcomes in the peptidome characterization and suggested that degradomic-peptidomic analysis of snake venoms is highly sensitive to the conditions of sampling procedures.

Nerve growth factor from Vipera lebetina venom

Nerve growth factor was isolated from the Vipera lebetina venom by a four-step procedure including gel filtration, ion exchange, heparin and hydrophobic chromatography. The purified protein is a glycosylated non-covalently bound homodimer with monomeric molecular mass of 14,380 Da. The cDNA encoding NGF is cloned and sequenced. The amino acid sequence translated from the cDNA comprises 117 or 119 amino acids depending on the N-terminus (truncated or not). The recombinant NGF (expressed in Escherichia coli) was used to prepare the anti-NGF antiserum. The antiserum interacted with the wild-type NGF and enabled to localize NGF during the purification procedure in parallel with MALDI-TOF analysis of tryptic peptides. The isolated NGF caused neurite outgrowth from PC12 cells in concentrations beginning from 2.5 ng/ml.

VGD and MLD-motifs containing heterodimeric disintegrin viplebedin-2 from Vipera lebetina snake venom. Purification and cDNA cloning

We have previously demonstrated that the fibrinolytic enzyme lebetase is synthesized with disintegrin-like domain that is cleaved posttranslationally (Siigur et al., 1996). Now we isolated a heterodimeric disintegrin viplebedin-2 containing this disintegrin-like part from Vipera lebetina venom using size-exclusion chromatography on Sephadex G-100 sf and HPLC on C18 column. The molecular masses of viplebedin-2 and tryptic peptides from both chains of viplebedin-2 were determined by MALDI-TOF mass spectrometry. Using cDNA library of the venom gland of a single V. lebetina turanica snake the viplebedin-2 coding cDNAs were cloned and sequenced. Viplebedin-2 chains are synthesized from two different genes. One chain, containing VGD sequence in disintegrin loop, is synthesized as a disintegrin-like part of the PII-type metalloprotease, lebetase. The other chain, containing MLD sequence in disintegrin loop, is synthesized from the gene without metalloproteinase domain. Two polyadenylation signal sequences have been found in MLD sequence coding chain precursor cDNAs. Viplebedin-2 dose-dependently inhibited adhesion of platelets to immobilized collagen and inhibited collagen-induced platelet aggregation.

Snake venom metalloproteases--structure and function of catalytic and disintegrin domains

Snake venoms are relevant sources of toxins that have evolved towards the engineering of highly active compounds. In the last years, research efforts have produced great advance in their understanding and uses. Metalloproteases with disintegrin domains are among the most abundant toxins in many Viperidae snake venoms. This review will focus on the structure, function and possible applications of the metalloprotease and disintegrin domains.

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.

A novel metalloprotease from Vipera lebetina venom induces human endothelial cell apoptosis

A novel endothelial cell apoptosis inducing metalloprotease (VLAIP) was found in the snake venom of Vipera lebetina. This metalloprotease is a heterodimeric glycoprotein with molecular mass of about 106 kDa. The protease hydrolyzes azocasein, fibrinogen and oxidized insulin B-chain. The enzyme readily hydrolyzes the Aalpha-chain and more slowly Bbeta-chain of fibrinogen. VLAIP does not cleave fibrin. The complete amino acid sequences of the two different monomers of VLAIP are deduced from the nucleotide sequences of cDNAs encoding these proteins. The full-length cDNA sequences of the VLAIP-A and VLAIP-B encode open reading frames of 616 and 614 amino acids that include signal peptide, propeptide and mature metalloproteinase with disintegrin-like and cysteine-rich domains. VLAIP belongs to the metalloprotease/disintegrin family of reprolysins and has high identity with the proteins that induce apoptosis of endothelial cells. Treatment of HUVEC cells with VLAIP induces changes in the attachment of cells to the substrate and causes cell death. We demonstrated that VLAIP inhibits endothelial cell adhesion to extracellular matrix proteins: fibrinogen, fibronectin, vitronectin, collagen I, and collagen IV. The induction of apoptosis by VLAIP was shown by means of a typical DNA fragmentation pattern of apoptotic cells as well as by monitoring phosphatidylserine externalization using annexin V-FITC staining and flow cytometric analysis.

A method for connecting solution-phase enzyme activity assays with immobilized format analysis by mass spectrometry

This paper reports an enzyme activity assay that combines the assets of both homogeneous and solid-phase formats. In this method, enzyme reactions are carried out in solution using substrates that are tagged with an immobilization reagent that allows the substrates to be selectively immobilized to self-assembled monolayers (SAMs), for direct analysis by matrix assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry (MS). As a model enzyme reaction, this work examined the transfer of a methyl group from S-adenosyl-l-methionine (AdoMet) to an arginine side chain of a peptide substrate by the enzyme protein arginine methyltransferase 1 (RMT1). A cysteine-terminated peptide substrate was methylated by RMT1 in solution and then applied to a maleimide-presenting SAM to give selective immobilization of the peptide. Time-dependent analysis of methylation using MALDI-TOFMS clearly showed that both the presence and relative amount of the two reaction products-the mono- and dimethylated peptides-can be conveniently evaluated. This assay strategy is rapid, takes advantage of solution-phase assay conditions, avoids the use of labels and complicated purification steps, and is applicable to multianalyte analyses.

Comparative analysis of the catalytic domain of hemorrhagic and non-hemorrhagic snake venom metallopeptidases using bioinformatic tools

Snake venom metalloproteases (SVMPs) are a set of interesting enzymes that are one of the major components of venom affecting hemostasis. A great challenge since their discovery has been to find molecular features responsible for their hemorrhagic potency and many attempts have been made without any consistent result. Here we describe a series of comparisons between the catalytic domains of hemorrhagic and non-hemorrhagic SVMPs made with the help of bioinformatics. These involved sequence and structure-based multiple alignments, phylogenetic reconstruction, predicted physical and chemical properties, motif scanning and structural analyses. Although hemorrhagic activity seems to be complex, involving multiple factors, we found some molecular characteristics that may influence the toxic effects. Among these findings, it was possible to use a molecular surface feature to subdivide the P-I class in hemorrhagic and non-hemorrhagic SVMPs. It was also possible to suggest a role for the conserved Asp148 and Ser176 residues in the stabilization of the active site.

Factor X activator from Vipera lebetina venom is synthesized from different genes

Vipera lebetina venom contains specific coagulant Factor X activator (VLFXA) that cleaves the Arg52-Ile53 bond in the heavy chain of human factor X. VLFXA is a glycoprotein that is composed of a heavy chain (HC) and two light chains (LC) linked by disulfide bonds. The complete amino acid sequences of the three chains of the factor X activator from V. lebetina snake venom are deduced from the nucleotide sequences of cDNAs encoding these chains. The full-length cDNA (2347 bp) sequence of the HC encodes an open reading frame (ORF) of 612 amino acids that includes signal peptide, propeptide and mature metalloproteinase with disintegrin-like and cysteine-rich domains. The light chain LC1 contains 123 and LC2 135 amino acid residues. Both light chains belong to the class of C-type lectin-like proteins. The N-termini of VLFXA chains and inner sequences of peptide fragments detected by liquid chromatography-electrospray ionization tandem mass spectrometry (LC MS/MS) from protein sequence are 100% identical to the sequences deduced from the cDNA. The molecular masses of tryptic fragments of VLFXA chains analyzed by matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) also confirm the protein sequences deduced from the cDNAs. These are the first cloned factor X activator heavy and light chains. We demonstrate that the heavy and light chains are synthesized from different genes.

The effect of post-translational modifications on the hemorrhagic activity of snake venom metalloproteinases

Metalloproteinases (MPs) are Zn(+)-dependent endoproteolytic enzymes, abundant in crotalid and viperid snake venoms. Most snake venom metalloproteinases (svMPs) are active on extracellular matrix components and this effect is thought to result in bleeding as a consequence of the basement membrane disruption in capillaries. Jararhagin and ACLH are hemorrhagic svMPs from Bothrops jararaca and Agkistrodon contortrix laticinctus venom, respectively. Both enzymes demonstrate proteolytic activity on fibrinogen and fibronectin and jararhagin inhibits collagen-induced platelet aggregation in vitro. This work describes the expression, purification and successful refolding of the recombinant ACLH zymogen (rPRO-ACLH) as well as the catalytic domain of jararhagin (rCDJARA). The heterologous proteins were produced in E. coli, an in vivo expression system that does not make post-translational modifications. The recombinant refolded proteins did not show any hemorrhagic activity in mice skin, as well as the native deglycosylated jararhagin and ACLH. However, they preserved their proteolytic activity on fibrinogen and fibronectin. It seems that the hemorrhagic properties of these hemorrhagins are dependent on post-translational modifications, whereas their proteolytic activity is not dependent on such modifications.

Metalloproteinase with factor X activating and fibrinogenolytic activities from Vipera berus berus venom

We have previously shown that Vipera berus berus venom contains several factor X activating enzymes. In the present study we have investigated one of them. The enzyme was separated from venom by gel filtration on Sephadex G-100 superfine and chromatography on agarose HPS-7 and phenyl-agarose. The enzyme is a glycosylated metalloproteinase containing hexoses, hexosamines and neuraminic acid. The purified factor X activating enzyme consists of two equal chains (59 kDa). The specificity studies have shown that enzyme is nonspecific factor X activating proteinase hydrolysing also proteins such as azocasein, gelatin and fibrinogen. The enzyme hydrolyses oxidized insulin B-chain at the positions Ala(14)-Leu(15) and Tyr(16)-Leu(17) but it is inactive on fibrin, plasminogen and prothrombin. We used 8-10 amino acid residues containing peptides, which reproduce the sequence around the cleavage sites in factor X, factor IX and fibrinogen, as potential substrates for enzyme. Cleavage products of peptide hydrolysis were determined by MALDI-TOF MS. The peptide Asn-Asn-Leu-Thr-Arg-Ile-Val-Gly-Gly-factor X fragment was cleaved by enzyme at positions Leu(3)-Thr(4) and Arg(5)-Ile(6). The fibrinogen peptide fragment Glu-Tyr-His-Thr-Glu-Lys-Leu-Val-Thr-Ser was hydrolysed at position Lys(6)-Leu(7).

Expression, refolding, and in vitro activation of a recombinant snake venom pro-metalloprotease

Metalloproteases comprise a family of Zn(2+)-endopeptidases that degrade most components of the extracellular matrix. Snake venoms are rich sources of metalloproteases, which also digest fibrinogen as well as fibrin, and in some cases, induce hemorrhage. A few low-molecular weight snake venom metalloproteases (svMPs) have been described as being devoid of hemorrhagic activity, but they have strong direct-acting fibrinolytic activity. This property could be very helpful in thrombosis therapy. ACLF is a fibrinolytic, non-hemorrhagic metalloprotease from the venom of the North American snake Agkistrodon contortrix laticinctus. We have developed an expression system for production of a recombinant pro-ACLF from a clone (ACLPREF) isolated from a venom gland cDNA library. The coding region including both the pro-enzyme domain and the mature protein domain was amplified by PCR and subcloned into the pET28a vector and the new plasmid was used to transform BL21(DE3) Escherichia coli cells. Culture of the transformants at 37 degrees C led to the overexpression of an insoluble 48kDa protein after induction with 1.0mM IPTG. The expressed protein was recovered from inclusion bodies with 6M buffered urea and purified by affinity chromatography under denaturing conditions. After dithiothreitol treatment, protein refolding was performed by gradual removal of the denaturing agent by dialysis. The pro-enzyme underwent auto-activation during refolding and it was active on fibrinogen and on a synthetic substrate. To control the activation step, the denaturing agent was rapidly removed to keep the protein in an unprocessed form, followed by later addition of Ca(2+) and Zn(2+) ions. This allowed controlling the enzyme activation, when it is needed.

Factor X activator from Vipera lebetina snake venom, molecular characterization and substrate specificity

Our studies of the venom from the Levantine viper Vipera lebetina have demonstrated the existence of both coagulants and anticoagulants of the hemostatic system in the same venom. We showed that V. lebetina venom contains factor X activator (VLFXA) and factor V activator, fibrinolytic enzymes. VLFXA was separated by gel filtration on Sephadex G-100 superfine and ion exchange chromatography on CM-cellulose and on TSK-DEAE (for HPLC) columns. VLFXA is a glycoprotein composed of a heavy chain (57.5 kDa) and two light chains (17.4 kDa and 14.5 kDa) linked by disulfide bonds. VLFXA has multiple molecular forms distinguished by their isoelectric points. The differences in their pI values may be caused by dissimilarities in the respective charged carbohydrate content or in the primary sequence of amino acids. We synthesized 6-9 amino acid residues containing peptides according to physiological cleavage regions of human factor X and human factor IX. The peptides (Asn-Asn-Leu-Thr-Arg-Ile-Val-Gly-Gly - factor X fragment, and Asn-Asp-Phe-Thr-Arg-Val-Val-Gly-Gly - factor IX fragment) were used as substrates for direct assay of VLFXA. Cleavage products of peptide hydrolysis and the molecular masses of cleavage products of human factor X were determined by MALDI-TOF MS. The MALDI-TOF MS was highly efficient for the recovery and identification of peptides released by VLFXA hydrolysis. We can conclude that VLFXA cleaves the Arg(52)-Ile(53) bond in the heavy chain of human factor X and the Arg(226)-Val(227) bond in human factor IX precursor. VLFXA could not activate prothrombin nor had any effect on fibrinogen, and it had no arginine esterase activity toward benzoylarginine ethyl ester.

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