L-异亮氨酸生产菌的苏氨酸脱水酶特性及应用OA

Threonine dehydratase(TD)is a key enzyme in the biosynthesis pathways of α-ketobutyrate and L-isoleucine,and its activity is subject to the feedback inhibition by L-isoleucine.In this study,sequence of TDYI from the L-isoleucine produc-ing strain Corynebacterium glutamicum YI was analyzed.The L-proline at 363rd site was substituted by L-leucine(P363L)in TDYI.Enzymatic assays demonstrated that the feedback inhibition by L-isoleucine of TDYI was abolished.Meanwhile,TDYI exhibited a Km of 8.7 mmol/L,a vmax of 88.2 μmol/(min·mg),a Kcat of 9.2 s-1,and a Kcat/Km of 1.06 L/(mmol·s).Its optimal pH and temperature were 7.0 and 35℃,respectively,similar with those of the wild-type TD,indicating that the P363L muta-tion did not markedly affect the catalytic performance of TDYI.Subsequently,TDYI were applied in biosynthesis of α-ketobutyrate and L-isoleucine,achieving a production of 13.3 and 5.3 g/L,respectively,significantly higher than those of the strains harboring TDM derived from Escherichia coli.This study identified and characterized TDYI,a feedback-inhibition-relieved threonine dehydratase from the industrial strain C.glutamicum YI.The findings provide a valuable reference for the biosynthesis of α-ketobutyrate,L-isoleucine,and their related products.