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  • Title: Effect of the hirudin carboxy-terminal peptide 54-65 on the interaction of thrombin with platelets.
    Author: Jandrot-Perrus M, Huisse MG, Krstenansky JL, Bezeaud A, Guillin MC.
    Journal: Thromb Haemost; 1991 Sep 02; 66(3):300-5. PubMed ID: 1746000.
    Abstract:
    The carboxy-terminal region of hirudin (residues 54-65) has previously been shown to inhibit thrombin clotting activity without binding to the catalytic site of the enzyme. In the present study, the effect of hirudin 54-65 on thrombin interaction with specified platelet proteins has been investigated. Hirudin 54-65 was found to inhibit thrombin-induced platelet aggregation and secretion in a dose-dependent manner. Substitution of either Phe56, Glu57, Ile59, Pro60 or Leu64 showed that these residues were critical for inhibition of thrombin-induced platelet activation whereas sulfation of Tyr63 increased the inhibitory potency of the peptide. Hydrolysis of glycoprotein V, a platelet membrane substrate for thrombin, was only partially inhibited by hirudin 54-65. Although hirudin 54-65 did not decrease the amount of thrombin bound to platelets during cross-linking experiments, it was found to inhibit the specific binding of thrombin to platelet glycoprotein Ib. Since the carboxy-terminal region of hirudin has previously been reported to bind near the trypsin-catalyzed beta cleavage site, we have analyzed the consequences of alpha to beta-thrombin conversion on both thrombin-hirudin 54-65 interaction and thrombin activity toward platelets. The beta cleavage induced a decrease in the affinity of thrombin for both glycoprotein Ib and hirudin 54-65. Altogether, our results indicate that thrombin recognition sites for hirudin 54-65 and platelet membrane glycoprotein Ib share common structures located near the beta cleavage site at Arg 73 on the thrombin B chain.
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