Blood coagulation factor Va's key interactive residues and regions for prothrombinase assembly and prothrombin binding

Blood coagulation factor Va serves an indispensable role in hemostasis as cofactor for the serine protease factor Xa. In the presence of an anionic phospholipid membrane and calcium ions, factors Va and Xa assemble into the prothrombinase complex. Following formation of the ternary complex with the macromolecular zymogen substrate prothrombin, the latter is rapidly converted into thrombin, the key regulatory enzyme of coagulation. Over the years, multiple binding sites have been identified in factor Va that play a role in the interaction of the cofactor with factor Xa, prothrombin, or the anionic phospholipid membrane surface. In this review, an overview of the currently available information on these interactive sites in factor Va is provided, and data from biochemical approaches and 3D structural protein complex models are discussed. The structural models have been generated in recent years and provide novel insights into the molecular requirements for assembly of both the prothrombinase and the ternary prothrombinase-prothrombin complexes. Integrated knowledge of functionally important regions in factor Va will allow for a better understanding of factor Va cofactor activity.

Blood coagulation factors V and VIII: Molecular Mechanisms of Procofactor Activation

A hallmark of hemostasis is that cells and proteins involved in the formation of a blood clot remain in a quiescent state and are only activated following an appropriate stimulus. The homologous proteins factors V and VIII cannot participate to any significant degree in their macromolecular enzyme complexes and are thus considered procofactors. Activity is generated following limited proteolysis, indicating that the conversion of the procofactors to factor Va and factor VIIIa must result in structural changes that impart cofactor function. The proteolytic events that lead to the activation of these proteins have been extensively characterized over the past three decades. However, a fundamental understanding of the mechanism(s) by which these proteins are kept as inactive procofactors and how specific bond cleavage facilitates the conversion to the active cofactor state is only starting to become known. These molecular processes undoubtedly play critical regulatory roles, evolved to maintain normal hemostasis since factor Va and factor VIIIa have a tremendous influence on thrombin generation. This review will detail our current understanding of the molecular process of procofactor activation and highlight structural features that play a major role in factor V and factor VIII activation.

Procoagulant adaptation of a blood coagulation prothrombinase-like enzyme complex in australian elapid venom

The macromolecular enzyme complex prothrombinase serves an indispensable role in blood coagulation as it catalyzes the conversion of prothrombin to thrombin, a key regulatory enzyme in the formation of a blood clot. Interestingly, a virtually identical enzyme complex is found in the venom of some Australian elapid snakes, which is composed of a cofactor factor Va-component and a serine protease factor Xa-like subunit. This review will provide an overview of the identification and characterization of the venom prothrombinase complex and will discuss the rationale for its powerful procoagulant nature responsible for the potent hemostatic toxicity of the elapid venom.

The molecular basis of factor V and VIII procofactor activation

Activation of precursor proteins by specific and limited proteolysis is a hallmark of the hemostatic process. The homologous coagulation factors (F)V and FVIII circulate in an inactive, quiescent state in blood. In this so-called procofactor state, these proteins have little, if any procoagulant activity and do not participate to any significant degree in their respective macromolecular enzymatic complexes. Thrombin is considered a key physiological activator, cleaving select peptide bonds in FV and FVIII which ultimately leads to appropriate structural changes that impart cofactor function. As the active cofactors (FVa and FVIIIa) have an enormous impact on thrombin and FXa generation, maintaining FV and FVIII as inactive procofactors undoubtedly plays an important regulatory role that has likely evolved to maintain normal hemostasis. Over the past three decades there has been widespread interest in studying the proteolytic events that lead to the activation of these proteins. While a great deal has been learned, mechanistic explanations as to how bond cleavage facilitates conversion to the active cofactor species remain incompletely understood. However, recent advances have been made detailing how thrombin recognizes FV and FVIII and also how the FV B-domain plays a dominant role in maintaining the procofactor state. Here we review our current understanding of the molecular process of procofactor activation with a particular emphasis on FV.