Raivio T L, Laird M W, Joly J C, Silhavy T J
Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
Mol Microbiol. 2000 Sep;37(5):1186-97. doi: 10.1046/j.1365-2958.2000.02074.x.
The Cpx envelope stress response of Escherichia coli is controlled by a two-component regulatory system that senses misfolded proteins in extracytoplasmic compartments and responds by inducing the expression of envelope protein folding and degrading factors. We have proposed that in the absence of envelope stress the pathway is maintained in a downregulated state, in part through interactions between the periplasmic inhibitor molecule CpxP and the sensing domain of the histidine kinase CpxA. In this study, we show that depletion of the periplasmic contents of the cell by spheroplast formation does indeed lead to induction of the Cpx envelope stress response. Further, removal of CpxP is an important component of this induction because tethering an MBP-CpxP fusion protein to the spheroplast inner membranes prevents full activation by this treatment. Spheroplast formation has previously been demonstrated to induce the expression of a periplasmic protein of unknown function, Spy. Analysis of spy expression in response to spheroplast formation by Western blot analysis and by lacZ operon fusion in various cpx mutant backgrounds demonstrated that spy is a member of the Cpx regulon. Interestingly, although the only known spy homologue is cpxP, Spy does not appear to perform the same function as CpxP as it is not involved in inhibiting the Cpx envelope stress response. Rather, deletion of spy leads to activation of the sigmaE stress response. Because the sigmaE response is specifically affected by alterations in outer membrane protein biogenesis, we think it possible that Spy may be involved in this process.
大肠杆菌的Cpx包膜应激反应由一个双组分调节系统控制，该系统可感知胞外区室中错误折叠的蛋白质，并通过诱导包膜蛋白折叠和降解因子的表达做出反应。我们提出，在没有包膜应激的情况下，该途径部分通过周质抑制剂分子CpxP与组氨酸激酶CpxA的传感结构域之间的相互作用维持在下调状态。在本研究中，我们表明通过原生质球形成耗尽细胞的周质内容物确实会导致Cpx包膜应激反应的诱导。此外，去除CpxP是这种诱导的一个重要组成部分，因为将MBP-CpxP融合蛋白拴系到原生质球内膜上可防止这种处理的完全激活。先前已证明原生质球形成可诱导一种功能未知的周质蛋白Spy的表达。通过蛋白质免疫印迹分析以及在各种cpx突变背景下通过lacZ操纵子融合分析对原生质球形成做出反应的spy表达，结果表明Spy是Cpx调节子的成员。有趣的是，尽管唯一已知的spy同源物是cpxP，但Spy似乎并不执行与CpxP相同的功能，因为它不参与抑制Cpx包膜应激反应。相反，spy的缺失会导致sigmaE应激反应的激活。由于sigmaE反应特别受外膜蛋白生物合成变化的影响，我们认为Spy可能参与了这一过程。
