Regulation of homoserine O-succinyltransferase for efficient production of L-methionine in engineered Escherichia coli.

l-Methionine biosynthesis in Eschericha coli consists of multiple unit modules with various enzymes involved and the imbalance between different modules always restricted its productivity. In this study, the key enzymes participating in the pathway were investigated for their effect on l-methionine production and the pivotal enzyme homoserine O-succinyltransferase (MetA) was designed to be regulated. The surface amino acid residues of MetA were effectively modified through site-saturation mutagenesis and single mutants L63F, A28V, P298L and double mutant L63F/A28V were obtained with improved l-methionine productivity. The structure analysis revealed that the involved residues were on the surface loop regions, which was proposed to be conducive to the refolding of MetA and thus reduce the inhibition effect caused by l-methionine. After expression of the selected single mutant L63F in engineered E. coli ΔIJA-HFEBC strain with l-methionine efflux pump and mutated 3-phosphoglycerate dehydrogenase, the l-methionine production was significantly improved, with a final yield of 3528 mg/L. The results demonstrated the efficiency of MetA regulation for enhanced production of l-methionine and meanwhile provided important guidance for further engineering of MetA with increased l-methionine productivity.