Role of the Residue L254 in the Substrate Recognition by Carboxypeptidase T from Thermoactinomyces Vulgaris Revealed by X-Ray Diffraction

The crystal structures of the L254N mutant of carboxypeptidase T in complexes with stable transition state analogs, such as sulfamoyl-L-glutamate, N-sulfamoyl-L-arginine, N-sulfamoyl-L-valine, and N-sulfamoyl-L-leucine, were determined at 2.05, 1.89, 2.30, and 1.79 Å resolution, respectively. The association constants of these inhibitors and the catalytic efficiency of the corresponding tripeptide substrates ZAAX were found to depend on the distances between the О15, О16, О20, and Т19 atoms of the ligand and the active-site residues N146, Y225, and E277 of the mutant protein. This dependence significantly differs from that found previously for wild-type carboxypeptidase T. These results demonstrate that leucine 254 of the flexible loop of metallocarboxypeptidases is involved in the substrate discrimination by carboxypeptidase T via the induced-fit mechanism.