title: Dominant negative lptE mutation that supports a role for LptE as a plug in the LptD barrel.
abstract: Lipopolysaccharide (LPS) is the major outer leaflet constituent of the Gram-negative outer membrane (OM) bilayer. A bipartite protein complex of LptD and LptE assembles LPS into the OM. It has been established that LptE assists folding and assembly of its β-barrel partner LptD, yet reported biochemical evidence suggested additional LptE functions. Here, we isolated dominant negative lptE mutations, seeking to inform these functions. The lptE14 mutation increased OM permeability to erythromycin, even when the wild-type lptE gene was present. We show that the lptE14 mutation does not cause a defect in either LptD assembly or LPS export. A spontaneous IS1 insertion in secA suppressed lptE14 erythromycin sensitivity by removing the C-terminal SecB-binding domain of SecA. While this suppressor mutation broadly impeded SecB-dependent secretion of preproteins, we show that suppression was a direct and specific consequence of reduced LptD levels in the OM. We suggest that lptE14 causes poor plugging of the LptD β barrel and that a reduction of ineffectively plugged LptD-LptE14 complexes in the OM decreases permeability to erythromycin. Hence, lptE14 supports a proposed plug-and-barrel LptE-LptD arrangement.
authors: Department of Molecular Biology, Princeton University, Princeton, New Jersey, USA.
authors: Marcin
authors: M
authors: Grabowicz
authors: Jennifer
authors: J
authors: Yeh
authors: Thomas J
authors: TJ
authors: Silhavy
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport; D002462:Cell Membrane / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004917:Erythromycin / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D019895:Transposases / Q000235:genetics
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C473497:IS1 transposase; D008070:Lipopolysaccharides; C475958:LptD protein, E coli; C514179:LptE protein, E coli; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; C057842:SecB protein, Bacteria; D004917:Erythromycin; D019895:Transposases; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins