Laboratory of Biochemistry and Genetics, NIDDK, National Institutes of Health, Bethesda, Maryland 20892.
Laboratory of Biochemistry and Genetics, NIDDK, National Institutes of Health, Bethesda, Maryland 20892.
J Biol Chem. 2013 Nov 22;288(47):33559-33570. doi: 10.1074/jbc.M113.510552. Epub 2013 Oct 4.
As part of our studies on the biological functions of polyamines, we have used a mutant of Escherichia coli that lacks all the genes for polyamine biosynthesis for a global transcriptional analysis on the effect of added polyamines. The most striking early response to the polyamine addition is the increased expression of the genes for the glutamate-dependent acid resistance system (GDAR) that is important for the survival of the bacteria when passing through the acid environment of the stomach. Not only were the two genes for glutamate decarboxylases (gadA and gadB) and the gene for glutamate-γ-aminobutyrate antiporter (gadC) induced by the polyamine addition, but the various genes involved in the regulation of this system were also induced. We confirmed the importance of polyamines for the induction of the GDAR system by direct measurement of glutamate decarboxylase activity and acid survival. The effect of deletions of the regulatory genes on the GDAR system and the effects of overproduction of two of these genes were also studied. Strikingly, overproduction of the alternative σ factor rpoS and of the regulatory gene gadE resulted in very high levels of glutamate decarboxylase and almost complete protection against acid stress even in the absence of any polyamines. Thus, these data show that a major function of polyamines in E. coli is protection against acid stress by increasing the synthesis of glutamate decarboxylase, presumably by increasing the levels of the rpoS and gadE regulators.
作为我们对多胺生物功能研究的一部分，我们使用了一种缺乏所有多胺生物合成基因的大肠杆菌突变体，进行了添加多胺对其全转录组影响的分析。添加多胺后最显著的早期反应是谷氨酸依赖型酸抗性系统（GDAR）基因表达增加，这对于细菌通过胃酸环境的生存至关重要。不仅谷氨酸脱羧酶（gadA 和 gadB）的两个基因和谷氨酸-γ-氨基丁酸转运体（gadC）的基因被多胺添加诱导，而且该系统的各种调节基因也被诱导。我们通过直接测量谷氨酸脱羧酶活性和酸存活来证实多胺对 GDAR 系统诱导的重要性。还研究了调节基因缺失对 GDAR 系统的影响以及这些基因中两个基因过表达的影响。引人注目的是，替代σ因子 rpoS 和调节基因 gadE 的过表达导致谷氨酸脱羧酶水平非常高，即使在没有任何多胺的情况下，也几乎完全免受酸应激。因此，这些数据表明，多胺在大肠杆菌中的主要功能是通过增加谷氨酸脱羧酶的合成来保护细菌免受酸应激，推测是通过增加 rpoS 和 gadE 调节剂的水平。
