The protein-disulfide isomerase DsbC cooperates with SurA and DsbA in the assembly of the essential β-barrel protein LptD.
The assembly of the β-barrel proteins present in the outer membrane (OM) of Gram-negative bacteria is poorly characterized. After translocation across the inner membrane, unfolded β-barrel proteins are escorted across the periplasm by chaperones that reside within this compartment. Two partially redundant chaperones, SurA and Skp, are considered to transport the bulk mass of β-barrel proteins. We found that the periplasmic disulfide isomerase DsbC cooperates with SurA and the thiol oxidase DsbA in the folding of the essential β-barrel protein LptD. LptD inserts lipopolysaccharides in the OM. It is also the only β-barrel protein with more than two cysteine residues. We found that surAdsbC mutants, but not skpdsbC mutants, exhibit a synthetic phenotype. They have a decreased OM integrity, which is due to the lack of the isomerase activity of DsbC. We also isolated DsbC in a mixed disulfide complex with LptD. As such, LptD is identified as the first substrate of DsbC that is localized in the OM. Thus, electrons flowing from the cytoplasmic thioredoxin system maintain the integrity of the OM by assisting the folding of one of the most important β-barrel proteins.
Denoncin
Katleen
K
de Duve Institute, Université catholique de Louvain, Brussels, Belgium.
Vertommen
Didier
D
Paek
Eunok
E
Collet
Jean-François
JF
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D019696:Peptidylprolyl Isomerase / Q000235:genetics / Q000378:metabolism*; D019704:Protein Disulfide-Isomerases / Q000235:genetics / Q000378:metabolism*; D053719:Tandem Mass Spectrometry; D013696:Temperature
D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; C475958:LptD protein, E coli; C490900:SurA protein, E coli; D019696:Peptidylprolyl Isomerase; D019704:Protein Disulfide-Isomerases; C526648:dsbA protein, E coli; C526649:dsbC protein, E coli