Cloned platelet thrombin receptor is necessary for thrombin-induced platelet activation.

Platelet activation by thrombin is critical for hemostasis and thrombosis. Structure-function studies with a recently cloned platelet thrombin receptor suggest that a hirudin-like domain in the receptor's extracellular amino terminal extension is a thrombin-binding determinant important for receptor activation. We now report that a peptide antiserum to this domain is a potent and specific antagonist of thrombin-induced platelet activation. This study demonstrates that the cloned platelet thrombin receptor is necessary for platelet activation by thrombin, and provides a strategy for developing blocking monoclonal antibodies of potential therapeutic value.