The structural elements of hirudin which bind to the fibrinogen recognition site of thrombin are exclusively located within its acidic C‐terminal tail

Abstract

Six lysyl residues of human thrombin (Lys^B21, Lys^B52, Lys^B65, Lys^B106, Lys^B107 and Lys^B154) have been previously shown to participate in the binding site of hirudin, a thrombin-specific inhibitor [(1989) J. Biol. Chem. 264, 7141-7146]. In this report, we attempted to delineate the region of hirudin which binds to these basic amino acids of thrombin. Using the N-terminal core domains (r-Hir^1–43 and r-Hir^1–52) derived from recombinant hirudins and synthetic C-terminal peptides (Hir^45–65 and Hir^52–65) - all fragments form complexes with thrombin — we are able to demonstrate that the structural elements of hirudin which account for the shielding of these 6 lysyl residues are exclusively located within the acidic C-terminal region. Since hirudin C-terminal peptides were shown to bind to a non-catalytic site of thrombin and inhibit its interaction with fibrinogen [(1987) FEBS Lett. 211, 10-16], our data consequently imply that these 6 lysyl residues are constituents of the fibrinogen recognition site of thrombin.