Ward Scott M, Bormans Arjan F, Manson Michael D
Department of Biology, 3258 TAMU, Texas A&M University, College Station, TX 77843, USA.
J Bacteriol. 2006 Jun;188(11):3944-51. doi: 10.1128/JB.00117-06.
Signal-transducing proteins that span the cytoplasmic membrane transmit information about the environment to the interior of the cell. In bacteria, these signal transducers include sensor kinases, which typically control gene expression via response regulators, and methyl-accepting chemoreceptor proteins, which control flagellar rotation via the CheA kinase and CheY response regulator. We previously reported that a chimeric protein (Nart) that joins the ligand-binding, transmembrane, and linker regions of the NarX sensor kinase to the signaling and adaptation domains of the Tar chemoreceptor elicits a repellent response to nitrate and nitrite. As with NarX, nitrate evokes a stronger response than nitrite. Here we show that mutations targeting a highly conserved sequence (the P box) in the periplasmic domain alter chemoreception by Nart and signaling by NarX similarly. In particular, the G51R substitution converts Nart from a repellent receptor into an attractant receptor for nitrate. Our results underscore the conclusion that the fundamental mechanism of transmembrane signaling is conserved between homodimeric sensor kinases and chemoreceptors. They also highlight the plasticity of the coupling between ligand binding and signal output in these systems.
跨越细胞质膜的信号转导蛋白将有关环境的信息传递到细胞内部。在细菌中，这些信号转导器包括传感器激酶，其通常通过响应调节因子控制基因表达，以及甲基接受化学感受器蛋白，其通过CheA激酶和CheY响应调节因子控制鞭毛旋转。我们之前报道过一种嵌合蛋白（Nart），它将NarX传感器激酶的配体结合、跨膜和连接区域与Tar化学感受器的信号传导和适应结构域连接起来，引发对硝酸盐和亚硝酸盐的排斥反应。与NarX一样，硝酸盐引发的反应比亚硝酸盐更强。在这里，我们表明，针对周质结构域中高度保守序列（P盒）的突变同样会改变Nart的化学感受和NarX的信号传导。特别是，G51R取代将Nart从硝酸盐的排斥受体转变为吸引受体。我们的结果强调了这样一个结论，即跨膜信号传导的基本机制在同二聚体传感器激酶和化学感受器之间是保守的。它们还突出了这些系统中配体结合和信号输出之间耦合的可塑性。
