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  • Title: Co-expression of feedback-resistant threonine dehydratase and acetohydroxy acid synthase increase L-isoleucine production in Corynebacterium glutamicum.
    Author: Yin L, Hu X, Xu D, Ning J, Chen J, Wang X.
    Journal: Metab Eng; 2012 Sep; 14(5):542-50. PubMed ID: 22771937.
    Abstract:
    Threonine dehydratase and acetohydroxy acid synthase are critical enzymes in the L-isoleucine biosynthesis pathway of Corynebacterium glutamicum, but their activities are usually feedback-inhibited. In this study, we characterized a feedback-resistant threonine dehydratase and an acetohydroxy acid synthase from an L-isoleucine producing strain C. glutamicum JHI3-156. Sequence analysis showed that there was only a single amino acid substitution (Phe383Val) in the feedback-resistant threonine dehydratase, and there were three mutated amino acids (Pro176Ser, Asp426Glu, and Leu575Trp) in the big subunit of feedback-resistant acetohydroxy acid synthase. The mutated threonine dehydratase over-expressed in E. coli not only showed completely resistance to L-isoleucine inhibition, but also showed enhanced activity. The mutated acetohydroxy acid synthase over-expressed in E. coli showed more resistance to L-isoleucine inhibition than the wild type. Over-expression of the feedback-resistant threonine dehydratase or acetohydroxy acid synthase in C. glutamicum JHI3-156 led to increase of L-isoleucine production; co-expression of them in C. glutamicum JHI3-156 led to 131.7% increase in flask cultivation, and could produce 30.7g/L L-isoleucine in 72-h fed-batch fermentation. These results would be useful to enhance L-isoleucine production in C. glutamicum.
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