Raivio T L, Silhavy T J
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9; Canada.
Annu Rev Microbiol. 2001;55:591-624. doi: 10.1146/annurev.micro.55.1.591.
Envelope stress responses play important physiological roles in a variety of processes, including protein folding, cell wall biosynthesis, and pathogenesis. Many of these responses are controlled by extracytoplasmic function (ECF) sigma factors that respond to external signals by means of a membrane-localized anti-sigma factor. One of the best-characterized, ECF-regulated responses is the sigma(E) envelope stress response of Escherichia coli. The sigma(E) pathway ensures proper assembly of outer-membrane proteins (OMP) by controlling expression of genes involved in OMP folding and degradation in response to envelope stresses that disrupt these processes. Prevailing evidence suggests that, in E. coli, a second envelope stress response controlled by the Cpx two-component system ensures proper pilus assembly. The sensor kinase CpxA recognizes misfolded periplasmic proteins, such as those generated during pilus assembly, and transduces this signal to the response regulator CpxR through conserved phosphotransfer reactions. Phosphorylated CpxR activates transcription of periplasmic factors necessary for pilus assembly.
包膜应激反应在多种过程中发挥重要的生理作用，包括蛋白质折叠、细胞壁生物合成和致病过程。许多此类反应由胞外功能（ECF）σ因子控制，这些因子通过膜定位的抗σ因子对外部信号作出反应。最具特征的ECF调控反应之一是大肠杆菌的σ（E）包膜应激反应。σ（E）途径通过控制参与外膜蛋白（OMP）折叠和降解的基因表达，以应对破坏这些过程的包膜应激，从而确保外膜蛋白的正确组装。现有证据表明，在大肠杆菌中，由Cpx双组分系统控制的第二种包膜应激反应可确保菌毛的正确组装。传感激酶CpxA识别错误折叠的周质蛋白，例如菌毛组装过程中产生的那些蛋白，并通过保守的磷酸转移反应将此信号传递给反应调节因子CpxR。磷酸化的CpxR激活菌毛组装所需的周质因子的转录。
