Department Biology I, Microbiology, Ludwig-Maximilians-University, Munich, Germany.
Mol Microbiol. 2010 Oct;78(2):271-7. doi: 10.1111/j.1365-2958.2010.07336.x.
In addition to stress-specific responses, most bacteria can mount a general stress response (GSR), which protects the cells against a wide range of unspecific stress conditions. The best-understood examples of GSR are the σ(B)-cascade of Bacillus subtilis and the RpoS response in Escherichia coli. While the latter is conserved in many other proteobacteria of the ß-, γ- and δ-clades, RpoS homologues are absent in α-proteobacteria and their GSR has long been a mystery. Recent publications finally unraveled the core of the GSR in this proteobacterial class, which is mediated by EcfG-like σ-factors. EcfG activity is controlled by NepR-like anti-σ factors and PhyR-like proteins that act as anti-anti-σ factors. These unusual hybrid proteins contain an N-terminal EcfG-like domain that acts as a docking interface for NepR, and a C-terminal receiver domain typical for bacterial response regulators. Upon phosphorylation, PhyR titrates NepR away from EcfG, thereby releasing the σ-factor to recruit RNA polymerase and initiate transcription of its target genes. In this issue of Molecular Microbiology, Herrou et al. describe the function and three-dimensional structure of PhyR from Caulobacter crescentus. This structure is key to understanding the mechanism of the reversible, phosphorylation-dependent partner switching module that orchestrates the GSR in α-proteobacteria.
除了特定压力反应外，大多数细菌还可以启动一般应激反应（GSR），以保护细胞免受广泛的非特异性应激条件的影响。GSR 最典型的例子是枯草芽孢杆菌的 σ(B)-级联和大肠杆菌中的 RpoS 反应。虽然后者在许多其他β-、γ-和δ- 分支的变形菌中都保守，但α-变形菌中没有 RpoS 同源物，它们的 GSR 一直是个谜。最近的出版物终于揭示了这个类别的 GSR 的核心，它是由 EcfG 样 σ 因子介导的。EcfG 活性受到 NepR 样抗 σ 因子和 PhyR 样蛋白的控制，它们作为抗抗 σ 因子发挥作用。这些不寻常的杂合蛋白包含一个 N 端 EcfG 样结构域，作为 NepR 的对接接口，以及一个 C 端典型的细菌反应调节剂的受体结构域。磷酸化后，PhyR 将 NepR 从 EcfG 上脱离下来，从而释放 σ 因子以招募 RNA 聚合酶并启动其靶基因的转录。在本期《分子微生物学》中，Herrou 等人描述了新月柄杆菌 PhyR 的功能和三维结构。这个结构是理解协调α-变形菌中可逆、磷酸化依赖的伙伴交换模块的机制的关键。
