Dissection of ?-barrel outer membrane protein assembly pathways through characterizing BamA POTRA 1 mutants of Escherichia coli.

ABSTRACT: BamA of Escherichia coli is an essential component of the hetero-oligomeric machinery that mediates ?-barrel outer membrane protein (OMP) assembly. The C- and N-termini of BamA fold into trans-membrane ?-barrel and five soluble POTRA domains respectively. Detailed characterization of BamA POTRA 1 missense and deletion mutants revealed two competing OMP assembly pathways, one of which is followed by the archetypal trimeric ?-barrel OMPs, OmpF and LamB, and is dependent on POTRA 1. Interestingly, our data suggest that BamA also requires its POTRA 1 domain for proper assembly. The second pathway is independent of POTRA 1 and is exemplified by TolC. Site-specific cross-linking analysis revealed that the POTRA 1 domain of BamA interacts with SurA, a periplasmic chaperone required for the assembly of OmpF and LamB, but not that of TolC and BamA. The data suggest that SurA and BamA POTRA 1 domain function in concert to assist folding and assembly of most ?-barrel OMPs except for TolC, which folds into a unique soluble ?-helical barrel and an OM-anchored ?-barrel. The two assembly pathways finally merge at some step beyond POTRA 1 but presumably before membrane insertion, which is thought to be catalysed by the trans-membrane ?-barrel domain of BamA.

SUBMITTER: Bennion D 

PROVIDER: S-EPMC2975826 | biostudies-literature | 2010 Sep

REPOSITORIES: biostudies-literature