Integration of Membrane Proteins into the Outer Membrane of Diderm Bacteria by the BAM Complex

Assembly of the outer membrane (OM) of diderm bacteria is coordinated by the essential β-barrel assembly machinery (BAM) and is critical for cellular survival and pathogenicity. BAM operates in a membrane environment that is highly rigid and spatiotemporally organized, and functions without ready access to an energy source. In addition, BAM interacts with many other proteins to efficiently fold outer membrane proteins (OMP), assemble complexes in the OM, and maintain cell envelope homeostasis. In recent years, great strides have been made toward understanding the molecular mechanism of BAM-mediated (OMP) folding, with structural biology used to visualize the different stages of the pathways of OMP folding and membrane insertion. The conformational cycling of BAM and its ability to transiently form hybrid barrels with substrate OMPs facilitates their folding. Both these mechanistic features appear to be well conserved and are attractive targets for antimicrobials.