Lipoprotein DolP supports proper folding of BamA in the bacterial outer membrane promoting fitness upon envelope stress.

David Ranava,Cyril Moulin,Catherine Turlan,Carine Froment,Raffaele Ieva,Gladys Munoz,Yiying Yang,Jérôme Rech,Lun Cui,Violette Morales,Luis Orenday-Tapia,Anne Caumont-Sarcos,François Rousset,Cécile Albenne,Julien Marcoux,David Bikard

doi:10.7554/elife.67817

Abstract

In Proteobacteria, integral outer membrane proteins (OMPs) are crucial for the maintenance of the envelope permeability barrier to some antibiotics and detergents. In Enterobacteria, envelope stress caused by unfolded OMPs activates the sigmaE (σE) transcriptional response. σE upregulates OMP biogenesis factors, including the β-barrel assembly machinery (BAM) that catalyses OMP folding. Here we report that DolP (formerly YraP), a σE-upregulated and poorly understood outer membrane lipoprotein, is crucial for fitness in cells that undergo envelope stress. We demonstrate that DolP interacts with the BAM complex by associating with outer membrane-assembled BamA. We provide evidence that DolP is important for proper folding of BamA that overaccumulates in the outer membrane, thus supporting OMP biogenesis and envelope integrity. Notably, mid-cell recruitment of DolP had been linked to regulation of septal peptidoglycan remodelling by an unknown mechanism. We now reveal that, during envelope stress, DolP loses its association with the mid-cell, thereby suggesting a mechanistic link between envelope stress caused by impaired OMP biogenesis and the regulation of a late step of cell division.

Highlights

The outer membrane (OM) of Gram-negative bacteria forms a protective barrier against harmful compounds, including several antimicrobials
Upon addition of 1 mM aTc to induce single guide RNAs (sgRNAs)-mediated targeting of dcas9 for approximately 17 generations, samples of cells from each culture were newly subjected to plasmid extraction and Illumina sequencing to determine the final distribution of sgRNA constructs. (C) Left: Comparison of gene scores obtained in dolP+ and DdolP screens
The x-axis shows a genetic interaction score calculated for each gene based on the minimum hypergeometric test conducted on the ranked difference of sgRNA-specific log2 fold-change (log2FC) values between the dolP and the dolP+ screens

Summary

Introduction

The outer membrane (OM) of Gram-negative bacteria forms a protective barrier against harmful compounds, including several antimicrobials. This envelope structure surrounds the inner membrane and the periplasm that contains the peptidoglycan, a net-like structure made of glycan chains and interconnecting peptides. At a late step of division, septal peptidoglycan synthesized by the divisome undergoes splitting, initiating the formation of the new poles of adjacent daughter cells. Remodelling of the OM barrier completes formation of the new poles in the cell offspring. The mechanisms by which cells coordinate OM remodelling with peptidoglycan splitting, preserving the permeability barrier of this protective membrane, are ill-defined (Egan et al, 2020)

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Conclusion