A novel snake venom C-type lectin-like protein modulates blood coagulation by targeting von Willebrand factor and coagulation factor IX.

Snake venom C-type lectin-like proteins (CLPs) belong to the nonenzymatic proteins. To date, no CLP with both platelet and coagulation factors activating activities has been reported. In this study, a novel CLP, termed protocetin, with molecular weight of 29.986 kDa, was purified from the Protobothrops mucrosquamatus venom (PMV). It consists of α- and β-chains, with 67% similarity in their N-terminal sequence. Protocetin activates glycoprotein Ib (GPIb) by binding to von Willebrand factor (vWF), inducing platelet aggregation. It also activates the intrinsic coagulation pathway by binding to coagulation factor IX. After injection of protocetin into mice at dose of 0.5 µg/g or 1.5 µg/g, it resulted in activation of platelets, a notable reduction in platelet count and prolonged tail bleeding time. Additionally, the plasma activated partial thromboplastin time (APTT) was significantly extended, and the fibrinogen concentration was markedly reduced. Thrombelastogram comfirmed the anticoagulation effect of protocetin. Notably, no microthrombosis was observed in tissues of lung, liver and kidney within 1 h after injection of protocetin into the mice at dose of 0.5 µg/g. This study revealed protocetin as a novel CLP from PMV that has dual functions in activating platelet and coagulation factor IX, thereby modulates coagulation in vivo. This work contributes to a better understanding of the structure and function of snake venom CLP.