Purification and characterization of kaouthiagin, a von Willebrand factor-binding and -cleaving metalloproteinase from Naja kaouthia cobra venom

A von Willebrand factor (vWF)-binding and -cleaving metalloproteinase, termed "kaouthiagin", was purified from the venom of cobra snake Naja kaouthia. Kaouthiagin is a monomer with a molecular mass of about 46 kDa and 51 kDa under non-reducing and reducing conditions, respectively, and the N-terminal amino acid sequence is homologous to high molecular mass snake venom metalloproteinases. Kaouthiagin bound to VWF in a divalent ion-independent manner, but the reduced kaouthiagin failed to interact with VWF, suggesting that the protein conformation maintained by intrachain-disulfide linkages of the molecule is essential for the binding to VWF. Neither botrocetin nor bitiscetin, vWF-binding modulators from another snake venom, interfered with the binding between kaouthiagin and vWF, but a monoclonal antibody VW92-3 specific to the N-terminal region of VWF (residues 1-910) inhibited the binding. Without affecting platelet GPIb/IX and GPIIb/IIIa, kaouthiagin specifically cleaved vWF between residues Pro-708 and Asp-709 in a divalent ion-dependent manner to diminish the multimeric structure of vWF in plasma, resulting in the loss of ristocetin-induced platelet aggregability and the collagen-binding activity of VWF. These results indicate that kaouthiagin is a unique metalloproteinase which specifically binds to and cleaves VWF at a specific site and that it will be a useful tool for functional dissection of VWF.