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

摘要

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 chromatogra-phy on Sephacryl S-200 and ion-exchange chromatography on CM Sepharose. The enzyme called leucurolysin-a (leuc-a), is a 23 kDa met-alloendopeptidase 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 NH_2-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/μg, respectively; crude venom = 8.0 units/mg and 9.5 units/μg). 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 Ala_(14)-Leu_(15) and Tyr_(16)-Leu_(17) 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 μg) subcutaneously into mice.