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Title: Triabin, a highly potent exosite inhibitor of thrombin. Author: Noeske-Jungblut C, Haendler B, Donner P, Alagon A, Possani L, Schleuning WD. Journal: J Biol Chem; 1995 Dec 01; 270(48):28629-34. PubMed ID: 7499380. Abstract: Triabin, a new thrombin inhibitor, has been purified from the saliva of Triatoma pallidipennis, a blood-sucking triatomine bug. It forms a noncovalent complex with thrombin at a molar ratio of 1:1, inhibits thrombin-induced platelet aggregation, and prolongs thrombin clotting time and activated partial thromboplastin time. However, it only minimally suppresses the amidolytic activity of thrombin, as measured by a chromogenic peptide substrate assay. It completely blocks trypsin-catalyzed cleavage of thrombin, probably via protection of the anion-binding exosite and inhibits the effect of thrombomodulin on thrombin in a dose-dependent fashion. These results indicate that the inhibitor is directed toward the anion-binding exosite of thrombin. The protein was partially sequenced and the information used to isolate cDNA clones from a T. pallidipennis salivary gland library. Four slightly polymorphic variants coding for mature proteins of 142 amino acids preceded by a putative leader sequence were obtained. The recombinant protein expressed in the periplasmic space of Escherichia coli has a biological activity similar to that of salivary triabin, as tested in a thrombin-induced platelet aggregation assay. In addition, recombinant triabin inhibits thrombin-catalyzed hydrolysis of fibrinogen with a Ki of about 3 pM.[Abstract] [Full Text] [Related] [New Search]