Lloyd Chelsea R, Park Seongjin, Fei Jingyi, Vanderpool Carin K
Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
Department of Biochemistry and Molecular Biology, University of Chicago, Institute for Biophysical Dynamics, Chicago, Illinois, USA.
J Bacteriol. 2017 May 9;199(11). doi: 10.1128/JB.00869-16. Print 2017 Jun 1.
The bacterial small RNA (sRNA) SgrS has been a fruitful model for discovery of novel RNA-based regulatory mechanisms and new facets of bacterial physiology and metabolism. SgrS is one of only a few characterized dual-function sRNAs. SgrS can control gene expression posttranscriptionally via sRNA-mRNA base-pairing interactions. Its second function is coding for the small protein SgrT. Previous work demonstrated that both functions contribute to relief of growth inhibition caused by glucose-phosphate stress, a condition characterized by disrupted glycolytic flux and accumulation of sugar phosphates. The base-pairing activity of SgrS has been the subject of numerous studies, but the activity of SgrT is less well characterized. Here, we provide evidence that SgrT acts to specifically inhibit the transport activity of the major glucose permease PtsG. Superresolution microscopy demonstrated that SgrT localizes to the cell membrane in a PtsG-dependent manner. Mutational analysis determined that residues in the N-terminal domain of PtsG are important for conferring sensitivity to SgrT-mediated inhibition of transport activity. Growth assays support a model in which SgrT-mediated inhibition of PtsG transport activity reduces accumulation of nonmetabolizable sugar phosphates and promotes utilization of alternative carbon sources by modulating carbon catabolite repression. The results of this study expand our understanding of a basic and well-studied biological problem, namely, how cells coordinate carbohydrate transport and metabolism. Further, this work highlights the complex activities that can be carried out by sRNAs and small proteins in bacteria. Sequencing, annotation and investigation of hundreds of bacterial genomes have identified vast numbers of small RNAs and small proteins, the majority of which have no known function. In this study, we explore the function of a small protein that acts in tandem with a well-characterized small RNA during metabolic stress to help bacterial cells maintain balanced metabolism and continue growing. Our results indicate that this protein acts on the glucose transport system, inhibiting its activity under stress conditions in order to allow cells to utilize alternative carbon sources. This work sheds new light on a key biological problem: how cells coordinate carbohydrate transport and metabolism. The study also expands our understanding of the functional capacities of small proteins.
细菌小RNA（sRNA）SgrS一直是发现新型RNA调控机制以及细菌生理学和代谢新方面的一个富有成果的模型。SgrS是少数几个已被表征的双功能sRNA之一。SgrS可以通过sRNA与mRNA的碱基配对相互作用在转录后控制基因表达。它的第二个功能是编码小蛋白SgrT。先前的研究表明，这两种功能都有助于缓解由磷酸葡萄糖应激引起的生长抑制，这种应激状态的特征是糖酵解通量中断和糖磷酸积累。SgrS的碱基配对活性已成为众多研究的主题，但SgrT的活性表征较少。在这里，我们提供证据表明SgrT的作用是特异性抑制主要葡萄糖通透酶PtsG的转运活性。超分辨率显微镜显示SgrT以PtsG依赖的方式定位于细胞膜。突变分析确定PtsG N端结构域中的残基对于赋予对SgrT介导的转运活性抑制的敏感性很重要。生长试验支持这样一个模型，即SgrT介导的对PtsG转运活性的抑制通过调节碳分解代谢物阻遏来减少不可代谢糖磷酸的积累并促进替代碳源的利用。这项研究的结果扩展了我们对一个基础且研究充分的生物学问题的理解，即细胞如何协调碳水化合物的运输和代谢。此外，这项工作突出了细菌中sRNA和小蛋白可以进行的复杂活动。对数百个细菌基因组的测序、注释和研究已经鉴定出大量的小RNA和小蛋白，其中大多数功能未知。在这项研究中，我们探索了一种小蛋白的功能，该小蛋白在代谢应激期间与一个已被充分表征的小RNA协同作用，以帮助细菌细胞维持代谢平衡并继续生长。我们的结果表明，这种蛋白作用于葡萄糖转运系统，在应激条件下抑制其活性，以便细胞能够利用替代碳源。这项工作为一个关键的生物学问题提供了新的线索：细胞如何协调碳水化合物的运输和代谢。该研究还扩展了我们对小蛋白功能能力的理解。
