title: Expression, purification, and inhibitory properties of human proteinase inhibitor.
abstract: In a previous report, the cDNA for human proteinase inhibitor 8 (PI8) was first identified, isolated, and subcloned into a mammalian expression vector and expressed in baby hamster kidney cells. Initial studies indicated that PI8 was able to inhibit the amidolytic activity of trypsin and form an SDS-stable approximately 67-kDa complex with human thrombin [Sprecher, C. A., et al. (1995) J. Biol Chem. 270, 29854-29861]. In the present study, we have expressed recombinant PI8 in the methylotropic yeast Pichia pastoris, purified the inhibitor to homogeneity, and investigated its ability to inhibit a variety of proteinases. PI8 inhibited the amidolytic activities of porcine trypsin, human thrombin, human coagulation factor Xa, and the Bacillus subtilis dibasic endoproteinase subtilisin A through different mechanisms but failed to inhibit the Staphylococcus aureus endoproteinase Glu-C. PI8 inhibited trypsin in a purely competitive manner, with an equilibrium inhibition constant (Ki) of less than 3.8 nM. The interaction between PI8 and thrombin occurred with a second-order association rate constant (kassoc) of 1.0 x 10(5) M-1 s-1 and a Ki of 350 pM. A slow-binding kinetics approach was used to determine the kinetic constants for the interactions of PI8 with factor Xa and subtilisin A. PI8 inhibited factor Xa via a two-step mechanism with a kassoc of 7.5 x 10(4) M-1 s-1 and an overall Ki of 272 pM. PI8 was a potent inhibitor of subtilisin A via a single-step mechanism with a kassoc of 1.16 x 10(6) M-1 s-1 and an overall Ki of 8.4 pM. The interaction between PI8 and subtilisin A may be of physiological significance, since subtilisin A is an evolutionary precursor to the intracellular mammalian dibasic processing endoproteinases.
authors.affiliation: Department of Pathology, University of New Mexico School of Medicine, Albuquerque 87131, USA.
authors.forename: J R
authors.initials: JR
authors.lastname: Dahlen
authors.forename: D C
authors.initials: DC
authors.lastname: Foster
authors.forename: W
authors.initials: W
authors.lastname: Kisiel
mesh_terms: D065427:Factor Xa Inhibitors; D006801:Humans; D007700:Kinetics; D008956:Models, Chemical; D010843:Pichia / Q000235:genetics; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology; D015843:Serpins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology*; D013917:Thrombin / Q000037:antagonists & inhibitors; D014357:Trypsin / Q000378:metabolism; D014361:Trypsin Inhibitors / Q000494:pharmacology
chemical_list: D065427:Factor Xa Inhibitors; D011994:Recombinant Proteins; C108403:SERPINB8 protein, human; D015843:Serpins; D014361:Trypsin Inhibitors; D014357:Trypsin; D013917:Thrombin