Joslin Stephanie N, Hendrixson David R
University of Texas Southwestern Medical School, Department of Microbiology, Dallas, TX 75390, USA.
J Bacteriol. 2008 Apr;190(7):2422-33. doi: 10.1128/JB.01827-07. Epub 2008 Jan 25.
Flagellar motility in Campylobacter jejuni mediates optimal interactions with human or animal hosts. Sigma(54) and the FlgSR two-component system are necessary for the expression of many C. jejuni flagellar genes. The FlgR response regulator is homologous to the NtrC family of transcriptional activators. These regulators usually contain an N-terminal receiver domain, a central domain that interacts with sigma(54) and hydrolyzes ATP, and a DNA-binding C-terminal domain. Most often, phosphorylation of the receiver domain influences its inherent ability to either positively or negatively control the activity of the regulator. In this study, we performed genetic and biochemical analyses to understand how FlgR activity is controlled to culminate in the expression of sigma(54)-dependent flagellar genes. Our data suggest that the FlgR receiver domain has the capacity for both positive and negative regulation in controlling the activation of the protein. Analysis of the C-terminal domain of FlgR revealed that it lacks a DNA-binding motif and is not required for sigma(54)-dependent flagellar gene expression. Further analysis of FlgR lacking the C-terminal domain indicates that this protein is partially functional in the absence of the cognate sensor kinase, FlgS, but its activity is still dependent on the phosphorylated residue in the receiver domain, D51. We hypothesize that the C-terminal domain may not function to bind DNA but may ensure the specificity of the phosphorylation of FlgR by FlgS. Our results demonstrate that FlgR activation mechanisms are unusual among characterized NtrC-like proteins and emphasize that various means are utilized by the NtrC family of proteins to control the transcription of target genes.
空肠弯曲杆菌的鞭毛运动介导了与人类或动物宿主的最佳相互作用。σ⁵⁴和FlgSR双组分系统对于许多空肠弯曲杆菌鞭毛基因的表达是必需的。FlgR反应调节蛋白与转录激活因子的NtrC家族同源。这些调节蛋白通常包含一个N端接收结构域、一个与σ⁵⁴相互作用并水解ATP的中央结构域以及一个DNA结合C端结构域。大多数情况下，接收结构域的磷酸化会影响其正向或负向控制调节蛋白活性的固有能力。在本研究中，我们进行了遗传和生化分析，以了解FlgR的活性是如何被控制从而最终导致σ⁵⁴依赖性鞭毛基因的表达。我们的数据表明，FlgR接收结构域在控制该蛋白的激活方面具有正向和负向调节的能力。对FlgR C端结构域的分析表明，它缺乏DNA结合基序，并且对于σ⁵⁴依赖性鞭毛基因的表达不是必需的。对缺失C端结构域的FlgR的进一步分析表明，该蛋白在没有同源传感激酶FlgS的情况下部分具有功能，但其活性仍然依赖于接收结构域中的磷酸化残基D51。我们推测，C端结构域可能不具有结合DNA的功能，但可能确保FlgS对FlgR磷酸化的特异性。我们的结果表明，FlgR激活机制在已表征的NtrC样蛋白中是不同寻常的，并强调NtrC家族蛋白利用各种方式来控制靶基因的转录。
