Crystal structure of γ-aminobutyrate aminotransferase in complex with a PLP-GABA adduct from Corynebacterium glutamicum

γ-Aminobutyrate (GABA), a four carbon non-protein amino acid, is used by some microorganisms as a source of carbon and/or nitrogen. Corynebacterium glutamicum has an incomplete GABA shunt that lacks a glutamate decarboxylase coding gene for the conversion of glutamate to GABA. Recently, a novel GABA assimilation system was identified in C. glutamicum. In the cell, GABA aminotransferase (GABA-AT) is the first step of GABA assimilation in the process of utilizing GABA as a carbon and/or nitrogen source. In this study, we report the crystal structure of CgGABA-AT in complex with PLP-GABA. We used structural studies and site-directed mutagenesis experiments to identify the key residues that contribute to the formation of the active site. Furthermore, based on structural comparisons and amino acid sequence alignment, we demonstrate the differences between the GABA-ATs of bacteria, fungi, and animals.