title: Mapping of the factor Xa binding site on factor Va by site-directed mutagenesis.
abstract: Activated coagulation factor V functions as a cofactor to factor Xa in the conversion of prothrombin to thrombin. Based on the introduction of extra carbohydrate side chains in recombinant factor V, we recently proposed several regions in factor Va to be important for factor Xa binding. To further define which residues are important for factor Xa binding, we prepared fifteen recombinant factor V variants in which clusters of charged amino acid residues were mutated, mainly to alanines. The factor V variants were expressed in COS-1 cells, and their functional properties evaluated in a prothrombinase-based assay, as well as in a direct binding test. Four of the factor V variants, 501A/510A/511D, 501A/510A/511D/513A, 513A/577A/578A, and 501A/510A/511D/513A/577A/578A exhibited markedly reduced factor Xa-cofactor activity tested in the prothrombinase assay, and reduced binding affinity as judged by the direct binding assay. These factor Va variants were normally cleaved at Arg-506 by activated protein C, and the interaction between the factor Xa-factor Va complex and prothrombin was unaffected by the introduced mutations. Based on the integration of all available data, we propose a key factor Xa binding surface to be centered on Arg-501, Arg-510, Ala-511, Asp-513, Asp-577, and Asp-578 in the factor Va A2 domain. These residues form an elongated charged factor Xa binding cluster on the factor Va surface.
authors.affiliation: Department of Laboratory Medicine, Division of Clinical Chemistry, Lund University, The Wallenberg Laboratory, MAS, SE-205 02 Malmö, Sweden.
authors.forename: Mårten
authors.initials: M
authors.lastname: Steen
authors.forename: Sinh
authors.initials: S
authors.lastname: Tran
authors.forename: Ludovic
authors.initials: L
authors.lastname: Autin
authors.forename: Bruno O
authors.initials: BO
authors.lastname: Villoutreix
authors.forename: Ann-Louise
authors.initials: AL
authors.lastname: Tholander
authors.forename: Björn
authors.initials: B
authors.lastname: Dahlbäck
mesh_terms: D000409:Alanine / Q000737:chemistry; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002522:Chlorocebus aethiops; D015943:Factor Va / Q000737:chemistry* / Q000235:genetics*; D015951:Factor Xa / Q000737:chemistry* / Q000235:genetics*; D006801:Humans; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D011485:Protein Binding; D011516:Prothrombin / Q000737:chemistry; D013816:Thermodynamics; D013925:Thromboplastin / Q000737:chemistry
chemical_list: D015943:Factor Va; D011516:Prothrombin; D013925:Thromboplastin; D015951:Factor Xa; D000409:Alanine