Dissection of β-barrel outer membrane protein assembly pathways through characterizing BamA POTRA 1 mutants of Escherichia coli.
BamA of Escherichia coli is an essential component of the hetero-oligomeric machinery that mediates β-barrel outer membrane protein (OMP) assembly. The C- and N-termini of BamA fold into trans-membrane β-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 β-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 β-barrel OMPs except for TolC, which folds into a unique soluble α-helical barrel and an OM-anchored β-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 β-barrel domain of BamA.
Bennion
Drew
D
School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA.
Charlson
Emily S
ES
Coon
Eric
E
Misra
Rajeev
R
D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense; D019696:Peptidylprolyl Isomerase / Q000378:metabolism; D017434:Protein Structure, Tertiary; D017384:Sequence Deletion
D001425:Bacterial Outer Membrane Proteins; C503914:BamA protein, E coli; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D050505:Mutant Proteins; C490900:SurA protein, E coli; D019696:Peptidylprolyl Isomerase