Estimation of the Possible Recognition Sites for Thrombomodulin, Procoagulant, and Anticoagulant Proteins around the Active Center of α-Thrombin1

alpha-Thrombin has several characteristic module structures around its active center. Previously we showed that a synthetic peptide, TWTANVGKGQPS, corresponding to the residues Thr147 to Ser158 of the B-chain of human thrombin, a possible interaction site of thrombomodulin near the active center of thrombin, specifically blocked the interactions between thrombin and thrombomodulin, fibrinogen, Factor V, or platelets [Suzuki, K. & Nishioka, J. (1991) J. Biol. Chem. 266, 18498-18501]. To elucidate further the role of the other module structures, we studied the effects of several synthetic peptides; FRKSPQELL, LLYPPWDKNF, RIGKHSRTRYER, LEKIYIHP, RYNWREN, DSTRIRI, EGDSGGP, and SWGEGCDRDGK, respectively corresponding to the residues Phe19 to Leu27, Leu45 to Phe54, Arg62 to Arg73, Leu81 to Pro88, Arg89 to Asn95, Asp175 to Ile181, Glu202 to Pro208, and Ser226 to Lys236 of the B-chain of human thrombin, which are located around the active center, as well as TWTANVGKGQPS, on the interaction between thrombin and thrombomodulin, protein C, fibrinogen, Factor V, antithrombin III, or hirudin. Thrombin-thrombomodulin interaction was inhibited significantly by RYNWREN as well as TWTANVGKGQPS, and partially by LLYPPWDKNF. The inhibitory effects of the two former peptides were additive and thrombomodulin directly bound to them. RYNWREN and TWTANVGKGQPS also increased the Km values 3-7 times for protein C as compared with the conditions without peptide. Thrombin-induced protein C activation in the absence of thrombomodulin was specifically blocked by EGDSGGP. Thrombin-induced fibrinogen clotting was blocked by FRKSPQELL, RIGKHSRTRYER as well as TWTANVGKGQPS at lower concentrations, and by RYNWREN and DSTRIRI at higher concentrations. Thrombin-induced Factor V activation was blocked by FRKSPQELL, RIGKHSRTRYER as well as TWTANVGKGQPS.(ABSTRACT TRUNCATED AT 250 WORDS)