Bacterial outer membrane proteins assemble via asymmetric interactions with the BamA ?-barrel.

ABSTRACT: The integration of ?-barrel proteins into the bacterial outer membrane (OM) is catalysed by the ?-barrel assembly machinery (BAM). The central BAM subunit (BamA) itself contains a ?-barrel domain that is essential for OM protein biogenesis, but its mechanism of action is unknown. To elucidate its function, here we develop a method to trap a native Escherichia coli ?-barrel protein bound stably to BamA at a late stage of assembly in vivo. Using disulfide-bond crosslinking, we find that the first ?-strand of a laterally 'open' form of the BamA ?-barrel forms a rigid interface with the C-terminal ?-strand of the substrate. In contrast, the lipid-facing surface of the last two BamA ?-strands forms weaker, conformationally heterogeneous interactions with the first ?-strand of the substrate that likely represent intermediate assembly states. Based on our results, we propose that BamA promotes the membrane integration of partially folded ?-barrels by a 'swing' mechanism.

SUBMITTER: Doyle MT 

PROVIDER: S-EPMC6659671 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature