细菌苏氨酸脱水酶受L-异亮氨酸反馈抑制的关键在于其调控结构域

苏氨酸脱水酶是细菌L-异亮氨酸合成途径中的关键酶,酶活力受终产物L-异亮氨酸的反馈抑制。苏氨酸脱水酶包含催化结构域及调控结构域,其中调控结构域所起的作用有待进一步研究。本文在大肠杆菌中分别克隆表达了四种不同的苏氨酸脱水酶:来自谷氨酸棒杆菌的苏氨酸脱水酶CgIlvA及其不合调控结构域的突变体CgIlvA~M和来自大肠杆菌的苏氨酸脱水酶EcIlvA及其不合调控结构域的突变体EcIlvA~M。通过蛋白纯化和酶活分析发现,CgIlvA~M和EcIlvA~M的酶活力比CgIlvA和EcIlvA的酶活力有所降低,但它们不再受L-异亮氨酸的反馈抑制,说明L-异亮氨酸对苏氨酸脱水酶的反馈抑制是通过其调控结构域来实现的。

Regulatory domain of bacterial threonine dehydratase,a key role in feedback inhibition of L-isoleucine

Threonine dehydratase is a key enzyme in the biosynthesis pathway of L-isoleucine, and its activity is inhibited by the end product L-isoleucine. Threonine dehydratase is composed of two domains, the catalytic domain and the regula- tory domain, but the role of the regulatory domain requires further study. In this work, four different threonine dehydrata- ses in E. coli, CgIlvA and CgIlvAM from Corynebacterium glutamicum as well as EcIlvA and EcIlvAM from Escherichia coli （ CgIlvAM and EcIlvAM, mutants of CgIlvA and EcIlvA by deleting the regulatory domain, respectively） were expressed. Enzyme activity analysis showed that activities of CgIlvAM and EcIlvAs were lower than those of CgIlvA and EcIlvA, respectively, but they were not inhibited by L-isoleucine. The results suggested the regulatory domain of threonine dehydratase played an important role in the L-isoleucine feedback inhibition to the enzyme activity.