Disulfide Rearrangement Triggered by Translocon Assembly Controls Lipopolysaccharide Export

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Science  30 Aug 2012:
DOI: 10.1126/science.1227215

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The presence of lipopolysaccharide (LPS) on the cell surface of Gram-negative bacteria is critical for viability. A conserved β-barrel membrane protein LptD translocates LPS from the periplasm across the outer membrane (OM). In Escherichia coli, this protein contains two disulfide bonds and forms the OM LPS translocon with the lipoprotein LptE. Here, we identified seven in vivo states on the oxidative folding pathway of LptD. Proper assembly involved a nonfunctional intermediate containing nonnative disulfides. Intermediate formation required the oxidase DsbA, and subsequent maturation to the active form with native disulfides was triggered by LptE. Thus, disulfide bond-dependent protein folding of LptD requires the proper assembly of a two-protein complex in order to promote disulfide bond rearrangement.

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