Location of the multimerin 1 binding site in coagulation factor V: An update

Abstract

Activated coagulation factor V (FVa) is an important cofactor that accelerates thrombin production. In human blood, 25% of the factor V (FV) is stored in platelets, complexed to the polymeric, FV binding protein multimerin 1 (MMRN1). The light chain of FV is required for MMRN1 binding, and its C2 domain contains a MMRN1 binding site that overlaps phospholipid binding residues essential for FVa procoagulant function. The homologous structures and roles of the FVa light chain C1 and C2 domains led us to investigate if the C1 domain also contains a MMRN1 binding site. The MMRN1 binding properties of FV constructs were tested by modified enzyme-linked immunoassays, before and after thrombin activation. The constructs tested included the combined C1 and C2 domain deleted FV, and B-domain deleted forms of FV containing C1 domain point mutations or combined C1 and C2 domain phospholipid binding site mutations. The MMRN1 binding site in FV/FVa was mapped to a large region that included the C1 domain phospholipid binding residues Y1956 and L1957. The FV construct with combined C1 and C2 domain phospholipid binding site mutations had no MMRN1 binding, highlighting the critical role of the FV C1 and C2 domain phospholipid binding residues in MMRN1 binding. Our data update the information on the structural features of FV and FVa important for MMRN1 binding, and suggest that the extended MMRN1 binding site in the C1 and C2 domains is important for the storage of FV-MMRN1 complexes in platelets.Activated FV (FVa) is a key coagulation cofactor that accelerates the production of thrombin by the prothrombinase complex [1]. In blood, approximately 25% of the factor V (FV) is retained in platelet α-granules, where FV is stored as a partially activated cofactor complexed to the polymeric protein multimerin 1 (MMRN1) [2,3]. In humans, MMRN1-FV binding is predominantly noncovalent, although 25% of platelet FV is disulfide linked to MMRN1 [3]. Noncovalent FV-MMRN1 binding involves an extended region of the FV light chain C2 domain, that overlaps the FVa membrane binding site [4]. Recently solved FVa crystal structures and mutagenesis studies of FV function have provided evidence that the C domains of FV use structurally similar features to promote FVa binding to phospholipid membranes [5][6][7][8]. Nonetheless, the functions of the FV C1 domain are not as well characterized as those of the C2 domain. The possibility that the C1 domain contributes to MMRN1 binding is supported by the absent MMRN1 binding of FV constructs lacking the entire light chain, compared to the impaired MMRN1 binding of FV constructs lacking only the C2 domain [4]. These observations led us to investigate a potential MMRN1 binding site in the FV C1 domain.

Severe thrombophilia in a factor V‐deficient patient homozygous for the Ala2086Asp mutation (FV Besançon)

“…23,24 Platelet FV originates from the internalization and subsequent processing of plasma FV by bone marrow megakaryocytes [25][26][27] and is stored in platelet α-granules in (mostly) noncovalent complexes with multimerin 1 (MMRN1), 28 which also binds to the C1 and C2 domains of FV. 29,30 Platelet FV is stored in a partially proteolysed form and is very resistant to APC-catalyzed inactivation. 31 Mutations in the F5 gene have been associated with both bleeding and thrombotic complications.…”