The CpxQ sRNA Negatively Regulates Skp To Prevent Mistargeting of β-Barrel Outer Membrane Proteins into the Cytoplasmic Membrane.

Marcin Grabowicz,Daria Koren,Thomas J Silhavy,Scott J Hultgren

doi:10.1128/mbio.00312-16

Abstract

ABSTRACTThe promoter most strongly induced upon activation of the Cpx two-component envelope stress response is the cpxP promoter. The 3′ untranscribed region (UTR) of the cpxP transcript is shown to produce a small RNA (sRNA), CpxQ. We investigated the role of CpxQ in combating envelope stress. Remarkably, the two effectors specified by the transcript are deployed to combat distinct stresses in different cellular compartments. CpxP acts in both a regulatory negative-feedback loop and as an effector that combats periplasmic protein misfolding. We find that CpxQ combats toxicity at the inner membrane (IM) by downregulating the synthesis of the periplasmic chaperone Skp. Our data indicate that this regulation prevents Skp from inserting β-barrel outer membrane proteins (OMPs) into the IM, a lethal event that likely collapses the proton motive force. Our findings suggest that Skp can fold and directly insert OMPs into a lipid bilayer in vivo without the aid of the Bam complex.

Highlights

The promoter most strongly induced upon activation of the Cpx two-component envelope stress response is the cpxP promoter
Zones of inhibition with incomplete clearance are given within parentheses
Despite being produced from the same mRNA, our results show that CpxP protein and CpxQ small RNA (sRNA) mature to become effectors lamB(A23D) ⌬skp::kan [18] [18] 0 a The zone of inhibition is the diameter of growth clearance minus the 6-mm disc

Summary

Introduction

The promoter most strongly induced upon activation of the Cpx two-component envelope stress response is the cpxP promoter. We show that the most highly expressed transcript of the Cpx stress response produces an sRNA from the 3= UTR, CpxQ, which combats this potential toxicity by downregulating Skp production. The complexity of coordinate envelope biogenesis during cell growth is underpinned by several stress response systems that sense envelope defects and alter gene expression to either alleviate or clear the damage [2]. Some of these systems are specific: for example, ␴E responds primarily to OM membrane defects [3, 4]. A second highly upregulated CpxR target is degP, which encodes a periplasmic protein with dual chaperone and protease function [14]

Methods

Results

Conclusion