Tick anticoagulant peptide: kinetic analysis of the recombinant inhibitor with blood coagulation factor X.alpha.

Publisher Website
Google Scholar
Abstract
Tick anticoagulant peptide (TAP) is a 60 amino acid protein which is a highly specific inhibitor of human blood coagulation factor Xa (fXa) isolated from the tick Ornithodoros moubata [Waxman, L., Smith, D. E., Arcuri, K. E., and Vlasuk, G. P. (1990) Science 248, 593-596]. Due to the limited quantities of native TPA, a recombinant version of TAP produced in Saccharomyces cervisiae was used for a detailed kinetic analysis of the inhibition interaction with human fXa. rTAP was determined to be reversible, slow, tight-binding inhibitor of fXa, displaying a competitive type of inhibition. The binding of rTAP to fXa is stoichiometric with a dissociation constant of (1.8 .+-. 0.02) .times. 10-10 M, a calculated association rate constant of (2.85 .+-. 0.07) .times. 106 M-1 s-1, and a dissociation rate constant of (0.554 .+-. 0.178) .times. 10-3 s-1. Binding studies show that 35S-rTAP binds only to fXa and not to DFP-treated fXa or zymogen factor X, which suggests the active site of fXa is required for rTAP inhibition. That rTAP is a unique serine proteinase inhibitor is suggested both by its high specificity for its target enzyme, fXa, and also by its unique structure.