title: Effect of heparin on the inhibition of factor Xa by tissue factor pathway inhibitor: a segment, Gly212-Phe243, of the third Kunitz domain is a heparin-binding site.
abstract: Tissue factor pathway inhibitor (TFPI) inhibits the tissue factor--factor VIIa complex and factor Xa with its first and second Kunitz domains (K1 and K2), respectively. The inhibitory activity is enhanced by heparin, and the C-terminal basic part has been shown to be a heparin-binding site (HBS-1). To characterize and localize a second heparin-binding site (HBS-2), we studied the effect of heparin on the inhibitory activity of two forms of recombinant human TFPI, the full-length TFPI (rTFPI), and TFPI lacking the C-terminal basic part (rTFPI-C), by assaying the inhibition of human factor Xa. rTFPI-C inhibited factor Xa with an initial Ki of 6.79 nM in the absence of Ca2+ and 22.3 nM in the presence of 5 mM CaCl2. Heparin decreased the initial Ki to 1.79 nM in the absence of Ca2+ and 2.68 nM in the presence of 5 mM CaCl2, indicating the presence of HBS-2 in rTFPI-C. The dissociation constant for the binding of HBS-2 with heparin was determined to be 830 nM using fluorescein-labeled heparin and rTFPI-C. Heparin enhanced the inhibitory activity of a fragment consisting of the K2 and K3 domains, but it did not stimulate the inhibitory activity of the K2 domain. A synthetic peptide mimicking from Gly212 to Phe243 in the K3 domain reduced the effect of heparin on the inhibition by rTFPI-C and rTFPI. These results defined the location of HBS-2 in the basic region of the K3 domain between Gly212 and Phe243.
authors.affiliation: National Cardiovascular Center Research Institute, Osaka, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Enjyoji
authors.forename: T
authors.initials: T
authors.lastname: Miyata
authors.forename: Y
authors.initials: Y
authors.lastname: Kamikubo
authors.forename: H
authors.initials: H
authors.lastname: Kato
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D065427:Factor Xa Inhibitors; D019793:Fluorescein; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006493:Heparin / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D008074:Lipoproteins / Q000737:chemistry* / Q000235:genetics / Q000494:pharmacology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000494:pharmacology; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology*
chemical_list: D065427:Factor Xa Inhibitors; D005452:Fluoresceins; D005456:Fluorescent Dyes; D008074:Lipoproteins; D010446:Peptide Fragments; D011994:Recombinant Proteins; D015842:Serine Proteinase Inhibitors; C051928:lipoprotein-associated coagulation inhibitor; D006493:Heparin; D002118:Calcium; D019793:Fluorescein