Catalytic properties and crystal structure of UDP-galactose 4-epimerase-like L-threonine 3-dehydrogenase from Phytophthora infestans

We report, for the first time, the three-dimensional structure and biochemical properties of a UDP-galactose 4-epimerase-like L-threonine 3-dehydrogenase (GalE-like L-ThrDH) from Phytophthora infestans, a plant disease-causing fungus. We identified GalE-like L-ThrDH using Kyoto Encyclopedia of Genes and Genomes (KEGG) database as a candidate target for the development of a new fungicide. The GalE-like L-ThrDH gene was expressed in Escherichia coli, and its product was purified and characterized. N-Acetylglycine was found to act as a competitive inhibitor of the enzyme (Ki = 0.18 mM). The crystal structure of the unique hexameric GalE-like L-ThrDH was determined using the molecular replacement method at a resolution of 2.3 angstrom, in the presence of NAD(+) and citrate, an analogue of the substrate. Based on the molecular docking simulation, N-acetylglycine molecule was modeled into the active site and the binding mode and inhibition mechanism of N-acetylglycine were elucidated.