Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045, USA.
J Bacteriol. 2011 Jan;193(2):389-98. doi: 10.1128/JB.00833-10. Epub 2010 Nov 5.
Two-component signal transduction systems are widespread in bacteria and are essential regulatory mechanisms for many biological processes. These systems predominantly rely on a sensor kinase to phosphorylate a response regulator for controlling activity, which is frequently transcriptional regulation. In recent years, an increasing number of atypical response regulators have been discovered in phylogenetically diverse bacteria. These atypical response regulators are not controlled by phosphorylation and exhibit transcriptional activity in their wild-type form. Relatively little is known regarding the mechanisms utilized by these atypical response regulators and the conserved characteristics of these atypical response regulators. Chlamydia spp. are medically important bacteria and encode an atypical OmpR/PhoB subfamily response regulator termed ChxR. In this study, protein expression analysis supports that ChxR is likely exerting its effect during the middle and late stages of the chlamydial developmental cycle, stages that include the formation of infectious elementary bodies. In the absence of detectable phosphorylation, ChxR formed homodimers in vitro and in vivo, similar to a phosphorylated OmpR/PhoB subfamily response regulator. ChxR was demonstrated to bind to its own promoter in vivo, supporting the role of ChxR as an autoactivator. Detailed analysis of the ChxR binding sites within its own promoter revealed a conserved cis-acting motif that includes a tandem repeat sequence. ChxR binds specifically to each of the individual sites and exhibits a relatively large spectrum of differential affinity. Taken together, these observations support the conclusion that ChxR, in the absence of phosphorylation, exhibits many of the characteristics of a phosphorylated (active) OmpR/PhoB subfamily response regulator.
双组分信号转导系统在细菌中广泛存在，是许多生物过程的重要调节机制。这些系统主要依赖于传感器激酶来磷酸化反应调节剂以控制活性，这通常是转录调控。近年来，在系统发育多样化的细菌中发现了越来越多的非典型反应调节剂。这些非典型反应调节剂不受磷酸化控制，在其野生型形式下表现出转录活性。关于这些非典型反应调节剂所利用的机制以及这些非典型反应调节剂的保守特征，人们知之甚少。衣原体属是医学上重要的细菌，编码一种称为 ChxR 的非典型 OmpR/PhoB 亚家族反应调节剂。在这项研究中，蛋白质表达分析支持 ChxR 可能在衣原体发育周期的中期和后期发挥作用，这包括形成传染性的原始体。在没有可检测到的磷酸化的情况下，ChxR 在体外和体内形成同源二聚体，类似于磷酸化的 OmpR/PhoB 亚家族反应调节剂。ChxR 被证明可以在体内与其自身启动子结合，支持 ChxR 作为自激活因子的作用。对其自身启动子内 ChxR 结合位点的详细分析揭示了一个保守的顺式作用基序，包括串联重复序列。ChxR 特异性地结合到每个单独的位点，并表现出相对较大的差异亲和力谱。综上所述，这些观察结果支持了这样的结论，即在没有磷酸化的情况下，ChxR 表现出许多磷酸化（活性）OmpR/PhoB 亚家族反应调节剂的特征。
