Binds to the subunit GPIbalpha (GP1BA) of the platelet GPIb/V/IX receptor system. It inhibits ristocetin- and vWF-induced platelet aggregation in platelet-rich plasma by inhibiting the binding of vWF to GPIbalpha. Heterodimer of subunits alpha and beta; disulfide-linked. Expressed by the venom gland. Belongs to the snaclec family.