The Synthetic Phenotype of ΔbamB ΔbamE Double Mutants Results from a Lethal Jamming of the Bam Complex by the Lipoprotein RcsF

Publication Year
2019

Type

Journal Article
Abstract
The selective permeability of the Gram-negative outer membrane (OM)
is maintained by integral -barrel outer membrane proteins (OMPs). The heteropentomeric
-barrel assembly machine (Bam) folds and inserts OMPs into the OM. Coordination
of the essential proteins BamA and BamD is critical for OMP assembly and
therefore the viability of the cell. The role of the nonessential lipoproteins BamBCE
has yet to be characterized; however, genetic evidence suggests that they have nonoverlapping
roles in OMP assembly. In this work, we quantify changes of the proteome
in the conditional lethal ΔbamB ΔbamE double mutant. We show that cells
lacking BamB and BamE have a global OMP defect that is a result of a lethal obstruction
of an assembly-competent Bam complex by the lipoprotein RcsF. RcsF is a
stress-sensing lipoprotein that is threaded through the lumen of abundant -barrel
OMPs by the Bam complex to expose the amino terminus on the cell surface. We
demonstrate that simply removing this lipoprotein corrects the severe OMP assembly
defect of the double mutant nearly as efficiently as a previously isolated suppressor
mutation in bamA. We propose that BamB and BamE play crucial, nonoverlapping
roles to coordinate the activities of BamA and BamD during OMP
biogenesis.
Journal
mBio
Volume
10
Issue
3
Pages
e00662-19