The Procoagulant Snake Venom Serine Protease Potentially Having a Dual, Blood Coagulation Factor V and X-Activating Activity.

A procoagulant snake venom serine protease was isolated from the venom of the nose-horned viper (Vipera ammodytes ammodytes). This 34 kDa glycoprotein, termedVaaSP-VX, possesses five kDa N-linked carbohydrates. Amino acid sequencing showedVaaSP-VX to be a chymotrypsin-like serine protease. Structurally, it is highly homologous toVaaSP-6 from the same venom and to nikobin from the venom ofVipera nikolskii, neither of which have known functions.VaaSP-VX does not affect platelets. The specific proteolysis of blood coagulation factors X and V by VaaSP-VX suggests that its blood-coagulation-inducing effect is due to its ability to activate these two blood coagulation factors, which following activation, combine to form the prothrombinase complex.VaaSP-VX may thus represent the first example of a serine protease with such a dual activity, which makes it a highly suitable candidate to replace diluted Russell's viper venom in lupus anticoagulant testing, thus achieving greater reliability of the analysis. As a blood-coagulation-promoting substance that is resistant to serpin inhibition,VaaSP-VX is also interesting from the therapeutic point of view for treating patients suffering from hemophilia.