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Abstract
Blood coagulation is a highly synchronized event of sequential activation reactions of several coagulation factors, and prothrombin activation is in the center of this cascade. In the physiological system, activated coagulation factor X (FXa) forms a complex (prothrombinase complex) with factor Va, Ca2+, and phospholipids and converts prothrombin to thrombin. Several exogenous prothrombin activators, particularly groups C and D from the Australian snake venoms, also activate prothrombin in a similar fashion. Recent studies have shown that they are structurally and functionally similar to the blood coagulation factors. Group C prothrombin activators resemble FVa-FXa complex, whereas group D prothrombin activators are similar to FXa. Thus, these snakes possess two parallel prothrombin activating systems, one in their venom and the other in their blood. These closely related proteins have distinctly different physiological roles. In this review, we will discuss the structural characteristics and evolution of the venom prothrombin activators and blood coagulation factors from Australian elapids.