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.
Highlights
Evolution has provided hematophageous animals with specific mechanisms to interfere with blood coagulation
The saliva of T. pallidipennis was found to inhibit platelet aggregation induced by collagen and aggregation mediated by thrombin
Other inhibitors from hematophageous animals form noncovalent complexes with thrombin but they differ in their mechanism of action
Summary
Evolution has provided hematophageous animals with specific mechanisms to interfere with blood coagulation. In contrast to the inhibitor from R. prolixus, the protein we isolated from T. pallidipennis and called triabin appears to be directed at the anion-binding exosite of thrombin. 20 l of thrombin (human from Sigma, 45 pM final concentration) were incubated with 80 l of 10 mM Tris-HCl, pH 7.4, 150 mM NaCl, and 100 l of inhibitor or buffer for 2 min at 37 °C
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
