The GLY1 gene of Saccharomyces cerevisiae encodes a low-specific L-threonine aldolase that catalyzes cleavage of L-allo-threonine and L-threonine to glycine - Expression of the gene in Escherichia coli and purification and characterization of the enzyme

The GLY1 gene of Saccharomyces cerevisiae is required for the biosynthesis of glycine for cell growth [McNeil, J. B., McIntosh, E. V., Taylor, B. V., Zhang, F.-R., Tang, S. & Bognar, A. L. (1994) J. Biol. Chem. 269, 9155-9165], but its gene product has not been identified. We have found that the GLY1 protein is similar in primary structure to L-allo-threonine aldolase of Aeromonas jandiae DK-39, which stereospecifically catalyzes the interconversion of L-allo-threonine and glycine. The GLY1 gene was amplified by PCR, with a designed ribosome-binding site, cloned into pUC118, and expressed in Escherichia coli cells. The enzyme was purified to homogeneity, as judged by polyacrylamide gel electrophoresis. The enzyme has a molecular mass of about 170 kDa and consists of four subunits identical in molecular mass. The enzyme contains 2 mol pyridoxal 5'-phosphate/4 mol of subunit as a cofactor, and its absorption spectrum exhibits maxims at 280 nm and 420 nm. The enzyme catalyzes the cleavage of not only L-allo-threonine to glycine but also L-threonine. We have termed the enzyme a low-specific L-threonine aldolase to distinguish it from L-allo-threonine aldolase.