The roles of factor Va and protein S in formation of the activated protein C/protein S/factor Va inactivation complex.

Magdalena Gierula, Isabelle I Salles-Crawley, Salvatore Santamaria, Adrienn Teraz-Orosz, James T B Crawley, David A Lane, Josefin Ahnström

Journal of thrombosis and haemostasis : JTH 2019 Dec

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Activated protein C (APC)-mediated inactivation of factor (F)Va is greatly enhanced by protein S. For inactivation to occur, a trimolecular complex among FVa, APC, and protein S must form on the phospholipid membrane. However, direct demonstration of complex formation has proven elusive. To elucidate the nature of the phospholipid-dependent interactions among APC, protein S, and FVa. We evaluated binding of active site blocked APC to phospholipid-coated magnetic beads in the presence and absence of protein S and/or FVa. The importance of protein S and FV residues were evaluated functionally. Activated protein C alone bound weakly to phospholipids. Protein S mildly enhanced APC binding to phospholipid surfaces, whereas FVa did not. However, FVa together with protein S enhanced APC binding (>14-fold), demonstrating formation of an APC/protein S/FVa complex. C4b binding protein-bound protein S failed to enhance APC binding, agreeing with its reduced APC cofactor function. Protein S variants (E36A and D95A) with reduced APC cofactor function exhibited essentially normal augmentation of APC binding to phospholipids, but diminished APC/protein S/FVa complex formation, suggesting involvement in interactions dependent upon FVa. Similarly, FVaNara (W1920R), an APC-resistant FV variant, also did not efficiently incorporate into the trimolecular complex as efficiently as wild-type FVa. FVa inactivation assays suggested that the mutation impairs its affinity for phospholipid membranes and with protein S within the complex. FVa plays a central role in the formation of its inactivation complex. Furthermore, membrane proximal interactions among FVa, APC, and protein S are essential for its cofactor function. © 2019 The Authors. Journal of Thrombosis and Haemostasis published by Wiley Periodicals, Inc. on behalf of International Society on Thrombosis and Haemostasis.

Citation

Magdalena Gierula, Isabelle I Salles-Crawley, Salvatore Santamaria, Adrienn Teraz-Orosz, James T B Crawley, David A Lane, Josefin Ahnström. The roles of factor Va and protein S in formation of the activated protein C/protein S/factor Va inactivation complex. Journal of thrombosis and haemostasis : JTH. 2019 Dec;17(12):2056-2068