Structure of Carboxypeptidase T from Thermoactinomyces Vulgaris in Complex with L-Phenyl Lactate

The crystal structure of metallocarboxypeptidase T (CPT) from Thermoactinomyces vulgaris in complex with L-phenyl lactate was determined at 1.73 Å resolution. As opposed to pancreatic carboxypeptidase A, which binds one L-phenyl lactate molecule, the ligand in the complex with CPT occupies simultaneously the S1 and S' subsites of the active site. This leads to conformational changes, which differ from those caused by the alternating occupation of the S1 and S1' subsites by tert-butyloxycarbonyl-L-leucine (BOC-leucine) and benzylsuccinic acid. These changes concern the residues E277, E59, L254, G192, S127, and Y218 and are up to 0.77 Å. A conclusion was drawn about the possible role of the residue E59 in the substrate recognition and catalysis by carboxypeptidase Т.