Alboaggregin-B and botrocetin, two snake venom proteins with highly homologous amino acid sequences but totally distinct functions on von Willebrand factor binding to platelets.

Alboaggregin-B (AL-B) (Peng et al., Biochemistry (1991) 30, 11529-11536) was highly purified from the snake venom of Trimeresurus albolabris and characterized structurally and functionally, comparing with botrocetin, another snake venom protein recently characterized (Usami et al., Proc. Natl. Acad. Sci. USA (1993) 90, 928-932). Both the venom proteins are a heterodimer and show a high degree of sequence homology to each other and also to C-type lectins. Botrocetin specifically binds to von Willebrand factor (vWF), whereas AL-B binds to platelet glycoprotein (GP) Ib without affecting the binding of botrocetin to vWF. The binding of AL-B to GPIb does not potentiate the platelet aggregation even by exogenous fibrinogen, suggesting that AL-B binding to GPIb does not activate GPIIb/IIIa complex.