Department of Biological Sciences, Life Science I, Virginia Polytechnic Institute and State University, Washington Street, Blacksburg, Virginia 24060, USA.
Biochemistry. 2010 Jul 20;49(28):5870-9. doi: 10.1021/bi100432e.
Pseudomonas aeruginosa, like many Gram-negative bacterial pathogens, requires its type III secretion system (T3SS) to facilitate acute infections. In P. aeruginosa, the expression of all T3SS-related genes is regulated by the transcriptional activator ExsA. A signaling cascade involving ExsA and three additional proteins, ExsC, ExsD, and ExsE, directly ties the upregulation of ExsA-mediated transcription to the activation of the type III secretion apparatus. In order to characterize the events underlying the signaling process, the crystal structure of the T3SS chaperone ExsC in complex with its cognate effector ExsE has been determined. The structure reveals critical contacts that mediate the interactions between these two proteins. Particularly striking is the presence of two Arg-X-Val-X-Arg motifs in ExsE that form identical interactions along opposite sides of an ExsC dimer. The structure also provides insights into the interactions of ExsC with the antiactivator protein ExsD. It was shown that the amino-terminal 46 residues of ExsD are sufficient for ExsC binding. On the basis of these findings, a new model for the ExsC.ExsD complex is proposed to explain its distinctive 2:2 stoichiometry and why ExsC displays a weaker affinity for ExsD than for ExsE.
铜绿假单胞菌与许多革兰氏阴性细菌病原体一样，需要其三型分泌系统（T3SS）来促进急性感染。在铜绿假单胞菌中，所有与 T3SS 相关的基因的表达都受转录激活因子 ExsA 的调控。涉及 ExsA 和另外三个蛋白（ExsC、ExsD 和 ExsE）的信号级联反应将 ExsA 介导的转录上调与 III 型分泌装置的激活直接联系起来。为了描述信号转导过程中的事件，已经确定了 T3SS 伴侣蛋白 ExsC 与其同源效应蛋白 ExsE 复合物的晶体结构。该结构揭示了介导这两种蛋白质相互作用的关键接触点。特别引人注目的是，ExsE 中存在两个 Arg-X-Val-X-Arg 基序，它们在 ExsC 二聚体的相对两侧形成相同的相互作用。该结构还提供了 ExsC 与反激活蛋白 ExsD 相互作用的见解。结果表明，ExsD 的氨基末端 46 个残基足以与 ExsC 结合。基于这些发现，提出了一个新的 ExsC.ExsD 复合物模型，以解释其独特的 2:2 化学计量比以及为什么 ExsC 与 ExsD 的亲和力比与 ExsE 的亲和力弱。
