Snake Venom Toxins Affecting Platelet Function

Botrocetin from the South American pit viper Bothrops jararaca was described as an activator of von Willebrand factor-dependent platelet aggregation by Read, Shermer, and Brinkhous in 1978 (1 ). Subsequently, botrocetin has been widely used as an important in vitro modulator in the analysis of von Willebrand factor and platelet aggregation. Botrocetin has since been identified as a heterodimer of the C-type lectin family of snake venom proteins (∼25 kDa nonreduced, ∼14 kDa reduced), the primary sequence and crystal structure have been determined, and specific binding sites within the A1 domain of von Willebrand factor have been identified (2 –8 ). Interestingly, members of the metalloproteinase-disintegrin family of snake venom proteins—jararhagin, jaracetin, and one-chain botrocetin—are functionally related to two-chain botrocetin, and also interact with the von Willebrand factor A1 domain (4 ,9 ,10 ). Jaracetin and one-chain botrocetin are variably processed forms of jararhagin and are found in the same viper species as the C-type lectin family, two-chain botrocetin. In this regard, recent evidence suggests that C-type lectin proteins and metalloproteinase-disintegrins may be derived from a common gene encoding a much larger precursor protein (11 ).