A new heat-shock gene, ppiD, encodes a peptidyl-prolyl isomerase required for folding of outer membrane proteins in Escherichia coli.
We have identified a new folding catalyst, PpiD, in the periplasm of Escherichia coli. The gene encoding PpiD was isolated as a multicopy suppressor of surA, a mutation which severely impairs the folding of outer membrane proteins (OMPs). The ppiD gene was also identified based on its ability to be transcribed by the two-component system CpxR-CpxA. PpiD was purified to homogeneity and shown to have peptidyl-prolyl isomerase (PPIase) activity in vitro. The protein is anchored to the inner membrane via a single transmembrane segment, and its catalytic domain faces the periplasm. In addition, we have identified by site-directed mutagenesis some of the residues essential for its PPIase activity. A null mutation in ppiD leads to an overall reduction in the level and folding of OMPs and to the induction of the periplasmic stress response. The combination of ppiD and surA null mutations is lethal. This is the first time two periplasmic folding catalysts have been shown to be essential. Another unique aspect of PpiD is that its gene is regulated by both the Cpx two-component system and the sigma32 heat shock factor, known to regulate the expression of cytoplasmic chaperones.
Département de Biochimie Médicale, Centre Médical Universitaire, 1 rue Michel-Servet, 1211 Genève 4, Switzerland.
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D001425:Bacterial Outer Membrane Proteins / Q000032:analysis / Q000737:chemistry*; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D001665:Binding Sites; D002238:Carbohydrate Epimerases / Q000235:genetics / Q000502:physiology; D002352:Carrier Proteins; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins; D005804:Genes, Lethal; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018869:Heat-Shock Response / Q000235:genetics; D008969:Molecular Sequence Data; D010755:Organophosphates / Q000494:pharmacology; D019696:Peptidylprolyl Isomerase / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011401:Promoter Regions, Genetic / Q000235:genetics; D017510:Protein Folding; D011494:Protein Kinases / Q000235:genetics; D011993:Recombinant Fusion Proteins; D018085:Regulon / Q000235:genetics; D015183:Restriction Mapping; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000235:genetics; D013489:Suppression, Genetic; D014158:Transcription, Genetic / Q000235:genetics
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; D010755:Organophosphates; D011993:Recombinant Fusion Proteins; C085504:CpxR protein, Bacteria; C011632:acetyl phosphate; D011494:Protein Kinases; C490475:CpxA protein, E coli; C092472:CpxA protein, bacteria; C037213:ADP-L-glycero-D-mannoheptose-6-epimerase; D002238:Carbohydrate Epimerases; C490900:SurA protein, E coli; C098640:periplasmic peptidylprolyl cis-trans isomerase; D019696:Peptidylprolyl Isomerase