Inhibition of thrombin's clotting activity by synthetic peptide segments of its inhibitors and substrates

Abstract

Synthetic peptides corresponding to segments of heparin cofactor II, fibrinogen, thrombomodulin, and hirudin were identified that inhibit thrombin's clotting of fibrinogen without blocking the enzyme's active site. Thrombin activity was inhibited 50% by the following peptide concentrations, with numbers in parenthesis indicating residues in the protein sequence: heparin cofactor II(54-75), 38 microM; heparin cofactor II(49-75), 28 microM; fibrinogen gamma B-chain(410-427), 130 microM; thrombomodulin(426-444), 140 microM; hirudin(54-65), 1.3 microM; hirudin(54-75)SO4, 0.17 microM. All of these peptides are likely to bind to thrombin's anion-binding exosite, suggesting that this site has broad sequence specificity such that it may participate in many of thrombin's interactions with physiological substrates and inhibitors.