Folding of a bacterial integral outer membrane protein is initiated in the periplasm.

ABSTRACT: The Bam complex promotes the insertion of ?-barrel proteins into the bacterial outer membrane, but it is unclear whether it threads ?-strands into the lipid bilayer in a stepwise fashion or catalyzes the insertion of pre-folded substrates. Here, to distinguish between these two possibilities, we analyze the biogenesis of UpaG, a trimeric autotransporter adhesin (TAA). TAAs consist of three identical subunits that together form a single ?-barrel domain and an extracellular coiled-coil ("passenger") domain. Using site-specific photocrosslinking to obtain spatial and temporal insights into UpaG assembly, we show that UpaG ?-barrel segments fold into a trimeric structure in the periplasm that persists until the termination of passenger-domain translocation. In addition to obtaining evidence that at least some ?-barrel proteins begin to fold before they interact with the Bam complex, we identify several discrete steps in the assembly of a poorly characterized class of virulence factors.

SUBMITTER: Sikdar R 

PROVIDER: S-EPMC5670179 | biostudies-literature | 2017 Nov

REPOSITORIES: biostudies-literature