Gierula M, Salles‐Crawley II, Santamaria S, Teraz‐Orosz A, Crawley JTB, Lane DA, Ahnström J. The roles of factor Va and protein S in formation of the activated protein C/protein S/factor Va inactivation complex.
J Thromb Haemost 2019;
17:2056-2068. [PMID:
31364267 PMCID:
PMC6916587 DOI:
10.1111/jth.14594]
[Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2019] [Accepted: 07/26/2019] [Indexed: 12/22/2022]
Abstract
BACKGROUND
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.
OBJECTIVES
To elucidate the nature of the phospholipid-dependent interactions among APC, protein S, and FVa.
METHODS
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.
RESULTS
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.
CONCLUSIONS
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.
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