Understanding the interaction of SurA and BAM in the outer membrane of E. coli

The outer membrane (OM) is a formidable barrier that protects Gram-negative bacteria against environmental threats. The correct folding and insertion of outer membrane proteins (OMPs) into the OM requires the essential OM-embedded β-barrel assembly machinery (BAM), a heptameric protein complex in E. coli. OMPs are delivered to BAM by the periplasmic chaperone SurA. However, how the activity of SurA and BAM are coordinated to ensure successful OMP delivery to BAM for folding into the OM remained unclear. We have trapped SurA in the act of OMP delivery to BAM and, via cryoEM, solved the structures of this assembly. By mutating key interaction sites we validate this interaction and use proteomics to determine how this perturbs the proteome of E. coli.