Department of Microbiology & Molecular Genetics, University of California, Irvine, CA 92697-4025, USA.
J Bacteriol. 2011 Dec;193(23):6733-41. doi: 10.1128/JB.05792-11. Epub 2011 Sep 30.
Chlamydial heat shock proteins have important roles in Chlamydia infection and immunopathogenesis. Transcription of chlamydial heat shock genes is controlled by the stress response regulator HrcA, which binds to its cognate operator CIRCE, causing repression by steric hindrance of RNA polymerase. All Chlamydia spp. encode an HrcA protein that is larger than other bacterial orthologs because of an additional, well-conserved C-terminal region. We found that this unique C-terminal tail decreased HrcA binding to CIRCE in vitro as well as HrcA-mediated transcriptional repression in vitro and in vivo. When we isolated HrcA from chlamydiae, we only detected the full-length protein, but we found that endogenous HrcA had a higher binding affinity for CIRCE than recombinant HrcA. To examine this difference further, we tested the effect of the heat shock protein GroEL on the function of HrcA since endogenous chlamydial HrcA has been previously shown to associate with GroEL as a complex. GroEL enhanced the ability of HrcA to bind CIRCE and to repress transcription in vitro, but this stimulatory effect was greater on full-length HrcA than HrcA lacking the C-terminal tail. These findings demonstrate that the novel C-terminal tail of chlamydial HrcA is an inhibitory region and provide evidence that its negative effect on repressor function can be counteracted by GroEL. These results support a model in which GroEL functions as a corepressor that interacts with HrcA to regulate chlamydial heat shock genes.
沙眼衣原体热休克蛋白在沙眼衣原体感染和免疫发病机制中具有重要作用。沙眼衣原体热休克基因的转录受应激反应调节剂 HrcA 控制，HrcA 通过空间位阻抑制 RNA 聚合酶与其同源操纵子 CIRCE 结合，从而抑制转录。所有沙眼衣原体均编码一种 HrcA 蛋白，由于其 N 端额外存在一个保守的 C 端区域，该蛋白比其他细菌的同源物更大。我们发现，这个独特的 C 端尾巴在体外和体内均降低了 HrcA 与 CIRCE 的结合，以及 HrcA 介导的转录抑制。当我们从衣原体中分离 HrcA 时，我们只检测到全长蛋白，但发现内源性 HrcA 与 CIRCE 的结合亲和力高于重组 HrcA。为了进一步研究这种差异，我们测试了热休克蛋白 GroEL 对 HrcA 功能的影响，因为内源性沙眼衣原体 HrcA 先前已被证明与 GroEL 作为复合物相关。GroEL 增强了 HrcA 与 CIRCE 结合和体外转录抑制的能力，但全长 HrcA 的这种刺激作用大于缺乏 C 端尾巴的 HrcA。这些发现表明，沙眼衣原体 HrcA 的新型 C 端尾巴是一个抑制区域，并提供了证据表明，其对抑制子功能的负效应可以被 GroEL 抵消。这些结果支持了一种模型，即 GroEL 作为一种核心抑制物与 HrcA 相互作用，以调节沙眼衣原体热休克基因。
