Importance of the Arg-Gly-Asp Triplet in Human Thrombin for Maintenance of Structure and Function

Site-directed mutagenesis was employed to assess the importance of the Arg-Gly-Asp triplet that comprises residues 197 to 199 in the B-chain of thrombin. Properties of the R197E and the D199E variants were compared with those of ζ-thrombin and the inactive S205A variant wherein the active site Ser is replaced by Ala. Relative to ζ-thrombin, the R197E thrombin variant under the assay conditions used exhibits 26% activity toward a small chromogenic substrate, 13% activity in the activation of protein C in the presence of thrombomodulin,