CRYSTAL-STRUCTURES OF L201A MUTANT OF D-AMINO-ACID AMINOTRANSFERASE AT 2.0 ANGSTROM RESOLUTION - IMPLICATION OF THE STRUCTURAL ROLE OF LEU201 IN TRANSAMINATION

The leucine-to-alanine mutation at residue 201 of D-amino acid aminotr ansferase provides a unique enzyme which gradually loses its activity while catalyzing the normal transamination; the co-enzyme form is conv erted from pyridoxal SI-phosphate to pyridoxamine 5'-phosphate upon th e inactivation [Kishimoto,K., Yoshimura,T., Esaki,N., Sugio,S., Mannin g,J.M. and Soda,K. (1995) J. Biochem., 117, 691-696]. Crystal structur es of both co-enzyme forms of the mutant enzyme have been determined a t 2.0 Angstrom resolution: they are virtually identical, and are quite similar to that of the wild-type enzyme. Significant differences in b oth forms of the mutant are localized only on the bound co-enzyme, the side chains of Lys145 and Tyr31, and a water molecule sitting on the putative substrate binding site, Detailed comparisons of the structure s of the mutant, together with that of the pyridoxamine-5'-phosphate f orm of the wild-type enzyme, imply that Leu201 would play a crucial ro le in the transamination reaction by keeping the pyridoxyl ring in the proper location without disturbing its oscillating motion, although t he residue seems to not be especially important for the structural int egrity of the enzyme.