Ministry of Education Key Laboratory of Protein Science, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China.
Cell Res. 2013 May;23(5):635-44. doi: 10.1038/cr.2013.13. Epub 2013 Jan 22.
Bacteria, exemplified by enteropathogenic Escherichia coli (E. coli), rely on elaborate acid resistance systems to survive acidic environment (such as the stomach). Comprehensive understanding of bacterial acid resistance is important for prevention and clinical treatment. In this study, we report a previously uncharacterized type of acid resistance system in E. coli that relies on L-glutamine (Gln), one of the most abundant food-borne free amino acids. Upon uptake into E. coli, Gln is converted to L-glutamate (Glu) by the acid-activated glutaminase YbaS, with concomitant release of gaseous ammonia. The free ammonia neutralizes proton, resulting in elevated intracellular pH under acidic environment. We show that YbaS and the amino acid antiporter GadC, which exchanges extracellular Gln with intracellular Glu, together constitute an acid resistance system that is sufficient for E. coli survival under extremely acidic environment.
以肠致病性大肠杆菌（E. coli）为代表的细菌依赖于精细的酸抗性系统来在酸性环境（如胃）中生存。全面了解细菌的酸抗性对于预防和临床治疗非常重要。在这项研究中，我们报告了大肠杆菌中一种以前未被描述的酸抗性系统，该系统依赖于 L-谷氨酰胺（Gln），这是最丰富的食物来源游离氨基酸之一。进入大肠杆菌后，Gln 被酸激活的谷氨酰胺酶 YbaS 转化为 L-谷氨酸（Glu），同时释放出氨气。游离氨中和质子，导致酸性环境下细胞内 pH 值升高。我们表明，YbaS 和氨基酸转运蛋白 GadC（它将细胞外的 Gln 与细胞内的 Glu 交换）共同构成了一种酸抗性系统，足以使大肠杆菌在极其酸性的环境中生存。
