Improved l-Leucine Production in by Optimizing the Aminotransferases.

The production of branched-chain amino acids (BCAAs) is still challenging, therefore we rationally engineered FA-1 to increase the l-leucine production by optimizing the aminotransferases. Based on this, we investigated the effects of the native aminotransferases, i.e., branched-chain amino acid aminotransferase (BCAT; encoded by ) and aspartate aminotransferase (AspB; encoded by ) on l-leucine production in C. glutamicum. The strain FA-1△ still exhibited significant growth without leucine addition, while FA-1△△ couldn't, which indicated that AspB also contributes to L-leucine synthesis in vivo and the yield of leucine reached 20.81 ± 0.02 g/L. It is the first time that AspB has been characterized for l-leucine synthesis activity. Subsequently, the aromatic aminotransferase TyrB and the putative aspartate aminotransferases, the , , gene products, were cloned, expressed and characterized for leucine synthesis activity in FA-1△△. Only TyrB was able to synthesize l-leucine and the l-leucine production was 18.55 ± 0.42 g/L. The two putative branched-chain aminotransferase genes, and , were also cloned and expressed. Both genes products function efficiently in BCAAs biosynthesis. This is the first report of a rational modification of aminotransferase activity that improves the l-leucine production through optimizing the aminotransferases.