Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas, United States of America.
Department of Pharmaceutical Chemistry, University of Kansas, Lawrence, Kansas, United States of America.
PLoS One. 2014 Mar 19;9(3):e91760. doi: 10.1371/journal.pone.0091760. eCollection 2014.
ChxR is an atypical two-component signal transduction response regulator (RR) of the OmpR/PhoB subfamily encoded by the obligate intracellular bacterial pathogen Chlamydia trachomatis. Despite structural homology within both receiver and effector domains to prototypical subfamily members, ChxR does not require phosphorylation for dimer formation, DNA binding or transcriptional activation. Thus, we hypothesized that ChxR is in a conformation optimal for DNA binding with limited interdomain interactions. To address this hypothesis, the NMR solution structure of the ChxR effector domain was determined and used in combination with the previously reported ChxR receiver domain structure to generate a full-length dimer model based upon SAXS analysis. Small-angle scattering of ChxR supported a dimer with minimal interdomain interactions and effector domains in a conformation that appears to require only subtle reorientation for optimal major/minor groove DNA interactions. SAXS modeling also supported that the effector domains were in a head-to-tail conformation, consistent with ChxR recognizing tandem DNA repeats. The effector domain structure was leveraged to identify key residues that were critical for maintaining protein - nucleic acid interactions. In combination with prior analysis of the essential location of specific nucleotides for ChxR recognition of DNA, a model of the full-length ChxR dimer bound to its cognate cis-acting element was generated.
ChxR 是专性细胞内细菌病原体沙眼衣原体编码的 OmpR/PhoB 亚家族的非典型双组分信号转导响应调节剂 (RR)。尽管在受体和效应结构域中都与典型亚家族成员具有结构同源性，但 ChxR 不需要磷酸化即可形成二聚体、结合 DNA 或转录激活。因此，我们假设 ChxR 处于与 DNA 结合的最佳构象，具有有限的结构域间相互作用。为了解决这个假设，确定了 ChxR 效应结构域的 NMR 溶液结构，并结合先前报道的 ChxR 受体结构域结构，根据 SAXS 分析生成了全长二聚体模型。ChxR 的小角度散射支持具有最小结构域间相互作用的二聚体，并且效应结构域的构象似乎只需要细微的重定向即可实现最佳的主/小沟 DNA 相互作用。SAXS 建模还支持效应结构域呈头对头构象，这与 ChxR 识别串联 DNA 重复序列一致。利用效应结构域结构来确定对维持蛋白质-核酸相互作用至关重要的关键残基。结合对特定核苷酸对于 ChxR 识别 DNA 的必需位置的先前分析，生成了全长 ChxR 二聚体与同源顺式作用元件结合的模型。
