Regulation and Function of the Envelope Stress Response Controlled by σE

Abstract

This chapter discusses regulation and function of the σ E envelope stress response. σ E is regulated by its antisigma factor, RseA. The cytoplasmic fragment of RseA is degraded by ClpXP, an ATPdependent cytoplasmic protease, and active σ E is released. This proteolytic cascade is activated by unassembled porins, which accumulate during appropriate envelope stress. Degradation of RseA by appropriate envelope stress releases σ E that is active for transcription. Two issues remain to be resolved concerning the proposed mechanism of induction. First, the critical contact between DegS and the porin is made by the -1 position of the peptide, an amino acid that is not a critical determinant of induction ability. Second, whereas wild-type (wt) DegS is active only in the presence of added C-terminal peptides, DegSΔPDZ cleaves RseA on its own. The current validated σ E regulon in E. coli K-12 is presented. It was recently shown that numerous proteins localized to the cytoplasmic membrane are controlled by σ 32, including two proteins essential for lipoprotein maturation: signal peptidase II and CutE. The porin signal allows the cell to use the σ E response to respond to general envelope stress as well as specific problems in porin/LPS status. The core function of the regulon is to maintain porin and lipopolysaccharide (LPS) homeostasis so that the barrier function of the cell is intact. The signal transduction system and the transcriptional circuitry of the core regulon are set up to ensure that this function is performed efficiently.