title: Ecotin is a potent inhibitor of the contact system proteases factor XIIa and plasma kallikrein.
abstract: Ecotin, a serine protease inhibitor found in the periplasm of Escherichia coli, has been characterized as a potent reversible tight-binding inhibitor of the human contact activation proteases factor XIIa (FXIIa) and plasma kallikrein, having Ki values of 89 pM and 163 pM, respectively. Ecotin also inhibited human leukocyte elastase (HLE) with high affinity (Ki = 55 pM). The association rate constants kon for FXIIa and kallikrein were 5.3 x 10(5) M-1.s-1 and 2.9 x 10(5) M-1.s-1, respectively. The dissociation rate constant koff for kallikrein, measured in the presence of HLE to prevent reassociation, was 6.3 x 10(-5) s-1; the koff for ecotin with FXIIa was 4.7 x 10(-5) s-1. Both FXIIa and kallikrein cleaved ecotin slowly at pH 5.0, identifying Met-84 as the P1 residue. The potent anticoagulant effect by ecotin is explained by the coincident inhibition of FXIIa, kallikrein, and FXa and suggests that it may be useful in the study of inflammatory or thrombotic disorders such as sepsis or cardiopulmonary bypass.
authors.affiliation: Department of Protein Engineering, Genentech Inc., South San Francisco, CA 94080, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: Ulmer
authors.forename: R N
authors.initials: RN
authors.lastname: Lindquist
authors.forename: M S
authors.initials: MS
authors.lastname: Dennis
authors.forename: R A
authors.initials: RA
authors.lastname: Lazarus
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000302:isolation & purification / Q000494:pharmacology*; D003001:Cloning, Molecular; D004789:Enzyme Activation; D004926:Escherichia coli; D029968:Escherichia coli Proteins; D015956:Factor XIIa / Q000037:antagonists & inhibitors*; D006801:Humans; D007610:Kallikreins / Q000037:antagonists & inhibitors*; D007700:Kinetics; D008969:Molecular Sequence Data; D033903:Periplasmic Proteins; D011485:Protein Binding; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000494:pharmacology; D013379:Substrate Specificity; D013997:Time Factors; D014361:Trypsin Inhibitors / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; C039076:Eco protein, E coli; D029968:Escherichia coli Proteins; D033903:Periplasmic Proteins; D011994:Recombinant Proteins; D014361:Trypsin Inhibitors; D007610:Kallikreins; D015956:Factor XIIa