Overproduction of NlpE, a new outer membrane lipoprotein, suppresses the toxicity of periplasmic LacZ by activation of the Cpx signal transduction pathway.
The LamB-LacZ-PhoA tripartite fusion protein is secreted to the periplasm, where it exerts a toxicity of unknown origin during high-level synthesis in the presence of the inducer maltose, a phenotype referred to as maltose sensitivity. We selected multicopy suppressors of this toxicity that allow growth of the tripartite fusion strains in the presence of maltose. Mapping and subclone analysis of the suppressor locus identified a previously uncharacterized chromosomal region at 4.7 min that is responsible for suppression. DNA sequence analysis revealed a new gene with the potential to code for a protein of 236 amino acids with a predicted molecular mass of 25,829 Da. The gene product contains an amino-terminal signal sequence to direct the protein for secretion and a consensus lipoprotein modification sequence. As predicted from the sequence, the suppressor protein is labeled with [3H]palmitate and is localized to the outer membrane. Accordingly, the gene has been named nlpE (for new lipoprotein E). Increased expression of NlpE suppresses the maltose sensitivity of tripartite fusion strains and also the extracytoplasmic toxicities conferred by a mutant outer membrane protein, LamBA23D. Suppression occurs by activation of the Cpx two-component signal transduction pathway. This pathway controls the expression of the periplasmic protease DegP and other factors that can combat certain types of extracytoplasmic stress.
Snyder
W B
WB
Department of Molecular Biology, Princeton University, New Jersey 08544, USA.
Davis
L J
LJ
Danese
P N
PN
Cosma
C L
CL
Silhavy
T J
TJ
D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000096:biosynthesis / Q000235:genetics*; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics*; D001483:Base Sequence; D016384:Consensus Sequence; D004789:Enzyme Activation / Q000235:genetics; D004794:Enzyme Repression / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D006360:Heat-Shock Proteins; D008074:Lipoproteins / Q000096:biosynthesis / Q000235:genetics*; D008320:Maltose / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D016366:Open Reading Frames; D033903:Periplasmic Proteins; D010957:Plasmids / Q000235:genetics; D011494:Protein Kinases; D012697:Serine Endopeptidases / Q000096:biosynthesis / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics*; D013489:Suppression, Genetic; D015533:Transcriptional Activation; D001616:beta-Galactosidase / Q000096:biosynthesis / Q000235:genetics / Q000633:toxicity*
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; D008074:Lipoproteins; C095021:NlpE protein, E coli; D033903:Periplasmic Proteins; D008320:Maltose; D011494:Protein Kinases; C490475:CpxA protein, E coli; C092472:CpxA protein, bacteria; D001616:beta-Galactosidase; C061682:DegP protease; D012697:Serine Endopeptidases