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J. Biol. Chem., Vol. 266, Issue 28, 18498-18501, 10, 1991
K Suzuki and J Nishioka
Thrombomodulin, a cofactor in the thrombin-catalyzed activation of protein
C, blocks the procoagulant activities of thrombin such as fibrinogen
clotting, Factor V activation, and platelet activation. The binding site
for thrombomodulin within human thrombin has been localized at a region
comprising residues Thr147-Ser158 of the B-chain of thrombin. The
dodecapeptide sequence, TWTANVGKGQPS, corresponding to these residues
inhibits thrombin binding to thrombomodulin with an apparent Ki = 94 microM
(Suzuki, K., Nishioka, J., and Hayashi, T. (1990) J. Biol. Chem. 265,
13263-13267). We have found that the inhibitory effect of the dodecapeptide
on the thrombin-thrombomodulin interaction is sequence-specific, and that
residues Asn151, Lys154, and Gln156 are essential for thrombomodulin
binding. The dodecapeptide was also found to directly block thrombin
procoagulant activities, fibrinogen clotting (concentration for
half-maximum inhibition, 385 microM). Factor V activation (concentration
for half-maximum inhibition, 33 microM), and platelet activation
(concentration for half- maximum inhibition, 645 microM). This peptide did
not block thrombin inhibition by antithrombin III, but blocked thrombin
inhibition by hirudin. These findings suggest that the binding site for
thrombomodulin in thrombin is shared with the sites for fibrinogen, Factor
V, platelets, and hirudin, and that, therefore, the inhibition of thrombin
procoagulant activities by thrombomodulin in part results from blocking of
the interaction between thrombin and the procoagulant protein substrates by
thrombomodulin.
A thrombin-based peptide corresponding to the sequence of the thrombomodulin-binding site blocks the procoagulant activities of thrombin
Department of Molecular Biology on Genetic Disease, Mie University School of Medicine, Japan.
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