CRYSTALLOGRAPHIC STUDY OF THE ASPARTATE-AMINOTRANSFERASE COMPLEX WITHD-ASPARTATE

The first X-ray crystallographic study was made on the complex of anim al aminotransferase with a D-amino acid at 2.5-Angstrom resolution. Cr ystals of the chicken heart cytosolic aspartate aminotransferase with D-aspartate were grown by cocrystallization (space group P2(1)2(1)2(1) , cell parameters a = 62.48 Angstrom, b = 117.71 Angstrom, c = 124.38 Angstrom, containing one dimeric protein molecule in the independent u nit). The 3D structure and changes therein were analyzed with computer graphics. D-Aspartate was found to bind in the active sites of both s ubunits, inducing significant conformational rearrangements of almost all active-site residues, which are most pronounced for Phe-18 and Glu -141. In both subunits of the complex the coenzyme pyridine ring is de formed, and the coenzyme swings about 90 degrees in the closed-confirm ation subunit. The substrate amino group appears to be the trigger of conformational alterations in the enzyme active site.