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

Abstract

Integral outer membrane proteins (OMPs) are crucial for the maintenance of the proteobacterial envelope permeability barrier to some antibiotics and detergents. In Enterobacteria, envelope stress caused by unfolded OM proteins (OMPs) activates the sigmaE (σE) transcriptional response. σE upregulates OMP-biogenesis factors, including the b-barrel assembly machinery (BAM) that catalyzes OMP folding. Here we report that DolP (formerly YraP), a σE-upregulated and poorly understood OM lipoprotein, is crucial for fitness in cells that undergo envelope stress. We demonstrate that DolP interacts with the BAM complex by associating to OM-assembled BamA. We provide evidence that DolP is important for proper folding of BamA that overaccumulates in the OM, thus supporting OMP biogenesis and OM 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.

A novel decoy strategy for polymyxin resistance in Acinetobacter baumannii

“…The Bam complex is an OM complex that mediates the folding and insertion of OM proteins into the membrane ( Malinverni and Silhavy, 2011 ). DolP, a lipoprotein, is known to promote proper folding of BamA, one of the essential subunits of the BAM complex, which might also play a role in OM integrity ( Ranava et al, 2021 ). Deletion of bamE in E. coli or in Salmonella enteritidis results in a more severe defect in OM and lower OM protein levels than does loss of bamC ( Sklar et al, 2007 ; Fardini et al, 2009 ).…”

BonA from Acinetobacter baumannii Forms a Divisome-Localized Decamer That Supports Outer Envelope Function

“…They lack conserved residues indicative of an enzyme active site, though some family members bind phospholipids ( 27 ). Archetypical members of this dual-BON domain family are the outer membrane-associated lipid-binding protein DolP (formerly YraP) and the soluble periplasmic protein OsmY, both of which play a role in the construction and maintenance of the bacterial outer envelope ( 25 – 29 ). OsmY is an abundant periplasmic protein in E. coli induced in response to stressors such as osmotic shock, heat shock, acidic pH, and bile salts ( 25 , 30 ).…”

“…DolP was initially identified in E. coli as a lipoprotein whose expression is induced under cell envelope stress and it forms part of the σ E regulon ( 35 ). Mutants of E. coli , N. meningitidis , and Salmonella enterica lacking DolP are compromised in outer membrane integrity, rendering the cells more sensitive to agents like the detergent sodium dodecyl sulfate (SDS) or the antibiotic vancomycin ( 26 , 27 , 29 , 33 , 35 , 36 ). Possibly as a result of impaired outer membrane integrity, loss of DolP leads to attenuation of virulence in rodent models of infection ( 26 ).…”

“…There has been significant recent progress in determining the function of DolP in E. coli , suggesting multifaceted roles in regulating cell division and aiding outer membrane protein insertion during protein folding stress ( 27 , 29 , 32 ); however, the mechanism by which DolP mediates these functions remains to be elucidated. In E. coli , DolP is recruited to the site of cell division through interaction with anionic phospholipids, mediated α-helix 1 of its C-terminal BON domain ( 27 , 32 ).…”

“…A recent study resolved the solution structure of DolP from E. coli , showing that it conforms to a dual-BON domain architecture and is monomeric ( 27 ). However, analysis of DolP isolated from E. coli membranes suggests that it forms oligomeric species ( 29 ). Furthermore, DolP interacts transiently with the BAM complex, which is responsible for the insertion of outer membrane proteins, and this interaction is important for coping with outer membrane protein folding stress ( 29 ).…”