Three-Dimensional Structures of Aspartate Aminotransferase from Escherichia coli and Its Mutant Enzyme at 2.5 Å Resolution

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Abstract
The structure of Escherichia cvli aspartate aminotransferase complex with the inhibitor 2-methylaspartate, and that of the mutant enzyme In which an arginine was substituted for a lysine residue thereby forming a Schiff base with the coenzyme pyridoxal 5′-phosphate, were determined at 2.5 Å resolution, by the molecular replacement method using the known structure of pig cytosolic aspartate aminotransferase. The enzyme catalyzes the reversible transainination between L-aspartate and α-ketoglutarate, and forms a dimeric structure of two identical subunits. Each subunit comprises two domains, a small and a large one. Although, in general, the overall and secondary structures of E. cvli enzyme are similar to those of higher animals, some differences of enzymatic action between the enzyme from E. cvli and those from higher animals could be explained on the basis of the X-ray structures and molecular mechanics calculation based on them.