Herrou Julien, Willett Jonathan W, Czyż Daniel M, Babnigg Gyorgy, Kim Youngchang, Crosson Sean
Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, USA.
Howard Taylor Ricketts Laboratory, University of Chicago, Chicago, Illinois, USA.
J Bacteriol. 2017 Feb 14;199(5). doi: 10.1128/JB.00746-16. Print 2017 Mar 1.
σ is an EcfG family sigma factor that regulates the transcription of dozens of genes in response to diverse stress conditions and is required for maintenance of chronic infection in a mouse model. A putative ATP-binding cassette transporter operon, , is among the most highly activated gene sets in the σ regulon. The proteins encoded by the operon resemble quaternary ammonium-compatible solute importers but are most similar in sequence to the broadly conserved YehZYXW system, which remains largely uncharacterized. Transcription of is activated by the general stress sigma factor σ in , which suggests a functional role for this transport system in bacterial stress response across the classes and We present evidence that YehZYXW does not function as an importer of known compatible solutes under physiological conditions and does not contribute to the virulence defect of a σ-null strain. The sole phenotype associated with genetic disruption of this putative transport system is reduced growth in the presence of high Li ion concentrations. A crystal structure of YehZ revealed a class II periplasmic binding protein fold with significant structural homology to ProX, which binds glycine betaine. However, the structure of the YehZ ligand-binding pocket is incompatible with high-affinity binding to glycine betaine. This is consistent with weak measured binding of YehZ to glycine betaine and related compatible solutes. We conclude that YehZYXW is a conserved, stress-regulated transport system that is phylogenetically and functionally distinct from quaternary ammonium-compatible solute importers. σ regulates transcription in response to stressors encountered in its mammalian host and is necessary for maintenance of chronic infection in a mouse model. The functions of the majority of genes regulated by σ remain undefined. We present a functional/structural analysis of a conserved putative membrane transport system (YehZYXW) whose expression is strongly activated by σ Though annotated as a quaternary ammonium osmolyte uptake system, experimental physiological studies and measured ligand-binding properties of the periplasmic binding protein (PBP), YehZ, are inconsistent with this function. A crystal structure of YehZ provides molecular insight into differences between bona fide quaternary ammonium osmolyte importers and YehZ-related proteins, which form a distinct phylogenetic and functional group of PBPs.
σ是一种EcfG家族的σ因子，可响应多种应激条件调节数十个基因的转录，并且是小鼠模型中维持慢性感染所必需的。一个假定的ATP结合盒转运蛋白操纵子是σ调控子中激活程度最高的基因集之一。该操纵子编码的蛋白质类似于季铵兼容溶质转运蛋白，但在序列上与广泛保守的YehZYXW系统最为相似，而该系统在很大程度上仍未被表征。在 中， 的转录由一般应激σ因子σ激活，这表明该转运系统在细菌跨 和 类别的应激反应中具有功能作用。我们提供的证据表明，YehZYXW在生理条件下不作为已知兼容溶质的转运蛋白，并且对σ缺失菌株的毒力缺陷没有影响。与该假定转运系统的基因破坏相关的唯一表型是在高锂离子浓度存在下生长减少。YehZ的晶体结构揭示了一种II类周质结合蛋白折叠，与结合甘氨酸甜菜碱的ProX具有显著的结构同源性。然而，YehZ配体结合口袋的结构与高亲和力结合甘氨酸甜菜碱不兼容。这与测得的YehZ与甘氨酸甜菜碱及相关兼容溶质的弱结合一致。我们得出结论，YehZYXW是一种保守的、应激调节的转运系统，在系统发育和功能上与季铵兼容溶质转运蛋白不同。σ响应其哺乳动物宿主中遇到的应激源调节转录，并且是小鼠模型中维持慢性感染所必需的。由σ调节的大多数基因的功能仍未确定。我们对一个保守的假定膜转运系统（YehZYXW）进行了功能/结构分析，其表达被σ强烈激活。尽管注释为季铵渗透溶质摄取系统，但实验生理学研究和周质结合蛋白（PBP）YehZ的测得配体结合特性与该功能不一致。YehZ的晶体结构提供了对真正的季铵渗透溶质转运蛋白和YehZ相关蛋白之间差异的分子见解，这些蛋白形成了一个独特的系统发育和功能组的PBPs。
