Eguchi Yoko, Itou Junji, Yamane Masatake, Demizu Ryo, Yamato Fumiyuki, Okada Ario, Mori Hirotada, Kato Akinori, Utsumi Ryutaro
Department of Bioscience, Graduate School of Agriculture, Kinki University, 3327-204, Nakamachi, Nara, 631-8505, Japan.
Proc Natl Acad Sci U S A. 2007 Nov 20;104(47):18712-7. doi: 10.1073/pnas.0705768104. Epub 2007 Nov 12.
Two-component signal-transduction systems (TCSs) of bacteria are considered to form an intricate signal network to cope with various environmental stresses. One example of such a network in Escherichia coli is the signal transduction cascade from the EvgS/EvgA system to the PhoQ/PhoP system, where activation of the EvgS/EvgA system promotes expression of PhoP-activated genes. As a factor connecting this signal transduction cascade, we have identified a small inner membrane protein (65 aa), B1500. Expression of the b1500 gene is directly regulated by the EvgS/EvgA system, and b1500 expression from a heterologous promoter simultaneously activated the expression of mgtA and other PhoP regulon genes. This activation was PhoQ/PhoP-dependent and EvgS/EvgA-independent. Furthermore, deletion of b1500 from an EvgS-activated strain suppressed mgtA expression. B1500 is localized in the inner membrane, and bacterial two-hybrid data showed that B1500 formed a complex with the sensor PhoQ. These results indicate that the small membrane protein, B1500, connected the signal transduction between EvgS/EvgA and PhoQ/PhoP systems by directly interacting with PhoQ, thus activating the PhoQ/PhoP system.
细菌的双组分信号转导系统（TCSs）被认为可形成一个复杂的信号网络来应对各种环境压力。大肠杆菌中这样一个网络的一个例子是从EvgS/EvgA系统到PhoQ/PhoP系统的信号转导级联，其中EvgS/EvgA系统的激活促进PhoP激活基因的表达。作为连接这个信号转导级联的一个因子，我们鉴定出了一种小的内膜蛋白（65个氨基酸），即B1500。b1500基因的表达直接受EvgS/EvgA系统调控，并且来自异源启动子的b1500表达同时激活了mgtA和其他PhoP调控子基因的表达。这种激活是PhoQ/PhoP依赖性的且EvgS/EvgA非依赖性的。此外，从EvgS激活的菌株中缺失b1500会抑制mgtA的表达。B1500定位于内膜，并且细菌双杂交数据表明B1500与传感器PhoQ形成了复合物。这些结果表明，小膜蛋白B1500通过直接与PhoQ相互作用连接了EvgS/EvgA和PhoQ/PhoP系统之间的信号转导，从而激活了PhoQ/PhoP系统。
