title: Probing the interface between factor Xa and tissue factor in the quaternary complex tissue factor-factor VIIa-factor Xa-tissue factor pathway inhibitor.
abstract: Blood coagulation is triggered by the formation of a complex between factor VIIa (FVIIa) and its cofactor, tissue factor (TF). TF-FVIIa is inhibited by tissue factor pathway inhibitor (TFPI) in two steps: first TFPI is bound to the active site of factor Xa (FXa), and subsequently FXa-TFPI exerts feedback inhibition of TF-FVIIa. The FXa-dependent inhibition of TF-FVIIa activity by TFPI leads to formation of the quaternary complex TF-FVIIa-FXa-TFPI. We used site-directed fluorescence probing to map part of the region of soluble TF (sTF) that interacts with FXa in sTF-FVIIa-FXa-TFPI. We found that the C-terminal region of sTF, including positions 163, 166, 200 and 201, is involved in binding to FXa in the complex, and FXa, most likely via its Gla domain, is also in contact with the Gla domain of FVIIa in this part of the binding region. Furthermore, a region that includes the N-terminal part of the TF2 domain and the C-terminal part of the TF1 domain, i.e. the residues 104 and 197, participates in the interaction with FXa in the quaternary complex. Moreover, comparisons of the interaction areas between sTF and FX(a) in the quaternary complex sTF-FVIIa-FXa-TFPI and in the ternary complexes sTF-FVII-FXa or sTF-FVIIa-FX demonstrated large similarities.
authors.affiliation: IFM-Department of Chemistry, Linköping University, Linköping, Sweden. msv@ifm.liu.se
authors.forename: Karin
authors.initials: K
authors.lastname: Carlsson
authors.forename: Per-Ola
authors.initials: PO
authors.lastname: Freskgård
authors.forename: Egon
authors.initials: E
authors.lastname: Persson
authors.forename: Uno
authors.initials: U
authors.lastname: Carlsson
authors.forename: Magdalena
authors.initials: M
authors.lastname: Svensson
mesh_terms: D019943:Amino Acid Substitution; D001665:Binding Sites; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics; D015942:Factor VIIa / Q000737:chemistry*; D015951:Factor Xa / Q000737:chemistry*; D005456:Fluorescent Dyes; D014644:Genetic Variation; D008074:Lipoproteins / Q000737:chemistry; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D010713:Phosphatidylcholines; D020836:Protein Structure, Quaternary; D011994:Recombinant Proteins / Q000737:chemistry; D013050:Spectrometry, Fluorescence
chemical_list: D005456:Fluorescent Dyes; D008074:Lipoproteins; D010713:Phosphatidylcholines; D011994:Recombinant Proteins; C051928:lipoprotein-associated coagulation inhibitor; D015942:Factor VIIa; D015951:Factor Xa