Synthesis of Oligopeptide Chloromethanes to Investigate Extended Binding Regions of Proteinases: Application to the Interaction of Fibrinogen with Thrombin

A method was established for the synthesis of oligopeptide chloromethanes which should be useful in the study of serine and cysteine proteinases with extended binding sites. The method involved condensation of an N-terminal peptide fragment obtained by solid-phase synthesis with a C-terminal peptide chloromethane synthesized by solution-phase chemistry. By using this procedure, oligopeptide chloromethanes of up to 16 residues were synthesized. These chloromethanes were based on the sequence of fibrinopeptide A. By using oligopeptide chloromethanes of different length, it was possible to show that the residues Asp7-Phe8-Leu9 play a crucial role in the recognition of fibrinopeptide A by thrombin. In contrast, the residues Ala1-Asp2-Ser3-Gly4-Glu5-Gly6 seem to play a minor role. Substitution of valine for Gly12, which occurs in a dysfibrinogenaemia, markedly decreased the rate of inactivation of thrombin by the oligopeptide chloromethane. The results are discussed in terms of the recently published structure of the complex between human thrombin and a chloromethane inhibitor based on fibrinopeptide A.