基于代谢流量分布信息理解大肠杆菌中异柠檬酸裂解酶调节因子的代谢调控作用

Metabolic regulation of isocitrate lyase regulator in Escherichia coli based on metabolic flux information

摘要:

基因的表达受不同的转录调节因子调节。大肠杆菌中的异柠檬酸裂解酶调节因子 (IclR) 能够抑制编码乙醛酸支路酶的aceBAK操纵子的表达。本研究基于代谢物的13C同位体物质分布来定量解析代谢反应，主要研究了iclR基因在大肠杆菌生理和代谢中的作用。大肠杆菌iclR基因缺失突变株的生长速率、糖耗速率和乙酸的产量相对于原始菌株都有所降低，但菌体得率略有增加。通过代谢途径的流量比率分析发现基因缺失株的乙醛酸支路得到了激活，33％的异柠檬酸流经了乙醛酸支路；戊糖磷酸途径的流量变小，使得CO2的生成量减少。同时，乙

Abstract:

Gene expression is regulated by different transcriptional regulators. The transcriptional regulator isocitrate lyase regulator (IclR) of Escherichia coli represses the expression of the aceBAK operon that codes for the glyoxylate pathway enzymes. In this study, physiological and metabolic responses of the deletion of the iclR gene in E. coli BW25113 were investigated based on the quantification and analysis of intracellular metabolic fluxes. The knockout of the iclR gene resulted in a decrease in the growth rate, glucose uptake rate and the acetate secretion rate, but a slight increase in biomass yield. The latter could be attributed to the lowered metabolic fluxes through several CO2 generating pathways, including the redirection of 33% of isocitrate directly to succinate and malate without CO2 production as well as the reduced flux through the pentose phosphate pathway. Furthermore, although the glyoxylate shunt was activated in the iclR mutant, the flux through phosphoenolpyruvate (PEP) carboxykinase kept almost unchanged, implying an inactive PEP-glyoxylate cycle and no extra loss of carbon atoms in the mutant strain. Both the reduced glucose uptake rate and the active glyoxylate shunt were responsible for the minor decrease in acetate secretion in the iclR knockout strain compared to that in the wild-type E. coli strain.