TA-2, a thrombin-like enzyme from the Chinese white-lipped green pitviper (Trimeresurus albolabris): isolation, biochemical and biological characterization.

Through three chromatographic steps, a new thrombin-like enzyme (TLE), named TA-2, from the venom of the Chinese white-lipped green pitviper (Trimeresurus albolabris) has been isolated and purified to homogeneity. TA-2 was a single-chain glycoprotein with about 6% sugar, pI 3.9 and a molecular weight of 38.8 kD. Its N-terminal sequence (VVGGDECNIN) showed high sequence conformity with many other TLEs. In vitro, it coagulated bovine fibrinogen (108.6 NIH units/mg) and cleaved the Aα and Bß chains of bovine fibrinogen-releasing fibrinopeptide A and B, but did not degrade bovine fibrin; displayed high stability at different temperature, pH, and presence of several divalent cations and inhibitors; also exhibited strong activity towards casein (192.3 units/mg) and high esterase activity upon Nα-p-tosyl-L-arginine methyl ester (11 units/mg); and behaved as a promoter to platelet aggregation induced by ADP or collagen. In vivo, TA-2 caused dose-dependent prolongation of bleeding time in mice, but had no hemorrhagic and edema-inducing activities even at high concentrations.

Expression and functional characterization of chitribrisin, a thrombin-like enzyme, in the venom of the Chinese green pit viper (Trimeresurus albolabris).

In the present study, functionally active, recombinant chitribrisin, which is a thrombin-like enzyme in the venom of the Chinese green pit viper (Trimeresurus albolabris), was expressed and purified using a prokaryotic system. The fusion protein of chitribrisin, together with TrxA and 6x His via an E.coli expression vector pET-32a(+), was successfully expressed in E.coli BL21(DE3) cells. After the fusion protein was isolated and purified by chelated Ni(2+) resin and specifically cleaved by enterokinase, the recombinant chitribrisin showed a strong fibrinogenolytic activity against the alpha and beta chains of human plasminogen-free fibrinogen and weak fibrinogen clotting activity. In addition, multiple sequence alignment revealed that the expressed chitribrisin was homologous to GPV-TL1 and GPV-TL2 from the snake venom of T. albolabris from central Thailand in terms of the amino acid sequence identities. However, there were some differences in the amino acid sequences of the proteins from the same species from different geographical locations. The causes for the geographical variation in TELs in the same species remain to be investigated. Mutagenesis of chitribrisin should be performed in future studies to study the structural and functional relationship and to identify the critical residues responsible for the properties of the thrombin-like enzyme.