Differential effects of yfgL mutation on Escherichia coli outer membrane proteins and lipopolysaccharide.
YfgL together with NlpB, YfiO, and YaeT form a protein complex to facilitate the insertion of proteins into the outer membrane of Escherichia coli. Without YfgL, the levels of OmpA, OmpF, and LamB are significantly reduced, while OmpC levels are slightly reduced. In contrast, the level of TolC significantly increases in a yfgL mutant. When cells are depleted of YaeT or YfiO, levels of all outer membrane proteins examined, including OmpC and TolC, are severely reduced. Thus, while the assembly pathways of various nonlipoprotein outer membrane proteins may vary through the step involving YfgL, all assembly pathways in Escherichia coli converge at the step involving the YaeT/YfiO complex. The negative effect of yfgL mutation on outer membrane proteins may in part be due to elevated sigma E activity, which has been shown to downregulate the synthesis of various outer membrane proteins while upregulating the synthesis of periplasmic chaperones, foldases, and lipopolysaccharide. The data presented here suggest that the yfgL effect on outer membrane proteins also stems from a defective assembly apparatus, leading to aberrant outer membrane protein assembly, except for TolC, which assembles independent of YfgL. Consistent with this view, the simultaneous absence of YfgL and the major periplasmic protease DegP confers a synthetic lethal phenotype, presumably due to the toxic accumulation of unfolded outer membrane proteins. The results support the hypothesis that TolC and major outer membrane proteins compete for the YaeT/YfiO complex, since mutations that adversely affect synthesis or assembly of major outer membrane proteins lead to elevated TolC levels.
Charlson
Emily S
ES
School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501, USA.
Werner
John N
JN
Misra
Rajeev
R
D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism* / Q000502:physiology; D015153:Blotting, Western; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D017353:Gene Deletion; D020043:Genes, Essential / Q000235:genetics / Q000502:physiology; D006360:Heat-Shock Proteins / Q000235:genetics / Q000502:physiology; D008070:Lipopolysaccharides / Q000378:metabolism*; D026901:Membrane Transport Proteins; D009097:Multienzyme Complexes / Q000378:metabolism; D033903:Periplasmic Proteins / Q000235:genetics / Q000502:physiology; D018272:Porins / Q000378:metabolism; D021382:Protein Sorting Signals; D021381:Protein Transport; D012697:Serine Endopeptidases / Q000235:genetics / Q000502:physiology
D001425:Bacterial Outer Membrane Proteins; C503914:BamA protein, E coli; C513739:BamD protein, E coli; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; C085044:LamB signal peptide, E coli; D008070:Lipopolysaccharides; D026901:Membrane Transport Proteins; D009097:Multienzyme Complexes; C113724:OmpC protein; D033903:Periplasmic Proteins; D018272:Porins; D021382:Protein Sorting Signals; C499985:YfgL protein, E coli; C073126:tolC protein, E coli; C078167:OMPA outer membrane proteins; C057843:envZ protein, E coli; C061682:DegP protease; D012697:Serine Endopeptidases