title: Tissue factor residues 157-167 are required for efficient proteolytic activation of factor X and factor VII.
abstract: The cell surface receptor tissue factor (TF) initiates coagulation by supporting the proteolytic activation of factors X and IX as well as VII to active serine proteases. Architectural similarity of TF to the cytokine receptor family suggests a strand-loop-strand structure for TF residues 151-174. Site-directed Ala exchanges in the predicted surface loop demonstrated that residues Tyr157, Lys159, Ser163, Gly164, Lys165, and Lys166 are important for function. Addition of side chain atoms at the Ser162 position decreased function, whereas the Ala exchange was tolerated. The dysfunctional mutants bound VII with high affinity and fully supported the catalysis of small peptidyl substrates by the mutant TF.VIIa complex. Lys159-->Ala substitution was compatible with efficient activation of factor X, whereas the Try157-->Ala exchange and mutations in the carboxyl aspect of the predicted loop resulted in diminished activation of factor X. The specific plasma procoagulant activity of all functionally deficient mutants increased 7- to 200-fold upon the supplementation of VIIa suggesting that TF residues 157-167 also provide important interactions that accelerate the activation of VII to VIIa. These data are consistent with assignment of the TF 157-167 region as contributing to protein substrate recognition and cleavage by the TF.VIIa complex.
authors.affiliation: Department of Immunology, Scripps Research Institute, La Jolla, California 92037.
authors.forename: W
authors.initials: W
authors.lastname: Ruf
authors.forename: D J
authors.initials: DJ
authors.lastname: Miles
authors.forename: A
authors.initials: A
authors.lastname: Rehemtulla
authors.forename: T S
authors.initials: TS
authors.lastname: Edgington
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D001777:Blood Coagulation; D010450:Endopeptidases / Q000737:chemistry; D005167:Factor VII / Q000737:chemistry / Q000378:metabolism*; D005170:Factor X / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship; D013925:Thromboplastin / Q000737:chemistry / Q000378:metabolism*
chemical_list: D009838:Oligodeoxyribonucleotides; D005167:Factor VII; D005170:Factor X; D013925:Thromboplastin; D010450:Endopeptidases