title: Interaction of hirudin with thrombin: identification of a minimal binding domain of hirudin that inhibits clotting activity.
abstract: Hirudin, isolated from the European leech Hirudo medicinalis, is a potent inhibitor of thrombin, forming an almost irreversible thrombin-hirudin complex. Previously, we have shown that the carboxyl terminus of hirudin (residues 45-65) inhibits clotting activity and without binding to the catalytic site of thrombin. In the present study, a series of peptides corresponding to this carboxyl-terminal region of hirudin have been synthesized, and their anticoagulant activity and binding properties to thrombin were examined. Binding was assessed by their ability to displace 125I-hirudin 45-65 from Sepharose-immobilized thrombin and by isolation of peptide-thrombin complexes. We show that the carboxyl-terminal 10 amino acid residues 56-65 (Phe-Glu-Glu-Ile-Pro-Glu-Glu-Tyr-Leu-Gln) are minimally required for binding to thrombin and inhibition of clotting. Phe-56 was critical for maintaining anticoagulant activity as demonstrated by the loss of activity when Phe-56 was substituted with D-Phe, Glu, or Leu. In addition, we found that the binding of the carboxyl-terminal peptide of hirudin with thrombin was associated with a significant conformational change of thrombin as judged by circular dichroism. This conformational change might be responsible for the loss of clotting activity of thrombin.
authors.affiliation: Merrell Dow Research Institute, Cincinnati, Ohio 45215.
authors.forename: S J
authors.initials: SJ
authors.lastname: Mao
authors.forename: M T
authors.initials: MT
authors.lastname: Yates
authors.forename: T J
authors.initials: TJ
authors.lastname: Owen
authors.forename: J L
authors.initials: JL
authors.lastname: Krstenansky
mesh_terms: D001665:Binding Sites; D002942:Circular Dichroism; D005260:Female; D006629:Hirudins / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D009842:Oligopeptides / Q000138:chemical synthesis / Q000378:metabolism / Q000494:pharmacology; D011485:Protein Binding; D011487:Protein Conformation; D013917:Thrombin / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D006629:Hirudins; D009842:Oligopeptides; D013917:Thrombin