Efficient Expression and Enzymatic Properties of L-Threonine Dehydrogenase from Escherichia coli

Our aim was to improve the catalytic efficiency of L-threonine dehydrogenase (L-TDH) on L-threonine dehydrogenation to synthesize ethyl L-2-aminoacetate. An L-TDH gene from Escherichia coli was mined and solubly expressed in E. coli BL21(DE3) through pACYCDuet-1 expression system. The expressed enzyme was purified and characterized. The results showed that high-level soluble expression of L-TDH was achieved in E. coli BL21(DE3), and the enzyme activity in the lysate was 19.13 IU/mL, which was about 79 times higher than that the level of E. coli BL21 (DE3) background expression. The specific activity of the purified L-TDH was 12.77 IU/mg; its optimal reaction temperature was 45 ℃, and its optimal reaction pH was 9.0. The residual enzyme activity was still more than 90% after being held at 35 or 40 ℃ for 120 min. In addition, the kinetic parameters of EcTDH were better than those of other reported L-TDHs, and EcTDH was superior in the synthesis of 2,5-dimethylpyrazine (2,5-DMP) by converting L-threonine. Our findings could lay a theoretical foundation for the industrial production of 2,5-DMP.