title: Inhibitory properties of human recombinant Arg24-->Gln type-2 tissue factor pathway inhibitor (R24Q TFPI-2).
abstract: Human type-2 tissue factor pathway inhibitor (TFPI-2), also known as placental protein 5, is a 32-kDa serine proteinase inhibitor consisting of three tandemly arranged Kunitz-type domains homologous to tissue factor pathway inhibitor. TFPI-2 inhibits a variety of serine proteinases involved in coagulation and fibrinolysis through an arginine residue (R24) in its first Kunitz-type domain, which constitutes a putative P1 residue for the substrate recognition sites of these proteinases. As recent studies have shown that this P1 residue to be a glutamine in murine TFPI-2, we constructed, expressed, and purified a human TFPI-2 mutant with glutamine substituted for arginine at position 24 (R24Q TFPI-2). R24Q TFPI-2 lost approximately 90% of its inhibitory activity towards bovine trypsin and virtually all inhibitory activity towards human plasmin and the factor VIIa-tissue factor complex, emphasizing the importance of the P1 Arg24 residue in the inhibition of these serine proteinases. However, whereas wild-type TFPI-2 is a relatively weak inhibitor of human factor Xa amidolytic activity (IC50 approximately 1 microM), R24Q TFPI-2 exhibited enhanced inhibitory activity towards the amidolytic and coagulant activities of this proteinase with a Ki of 18 nM. While the molecular basis for the enhanced inhibition of human factor Xa by R24Q TFPI-2 is unknown, these data provide suggestive evidence that murine TFPI-2 may function as a serine proteinase inhibitor in spite of the absence of a P1 Arg or Lys residue.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004591:Electrophoresis, Polyacrylamide Gel; D006023:Glycoproteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000302:isolation & purification; D006801:Humans; D007223:Infant; D008969:Molecular Sequence Data; D017354:Point Mutation; D011257:Pregnancy Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000302:isolation & purification; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology*