title: Phosphoethanolamine substitution in the lipid A of Escherichia coli O157 : H7 and its association with PmrC.
abstract: This study shows that lipid A of Escherichia coli O157 : H7 differs from that of E. coli K-12 in that it has a phosphoform at the C-1 position, which is distinctively modified by a phosphoethanolamine (PEtN) moiety, in addition to the diphosphoryl form. The pmrC gene responsible for the addition of PEtN to the lipid A of E. coli O157 : H7 was inactivated and the changes in lipid A profiles were assessed. The pmrC null mutant still produced PEtN-modified lipid A species, albeit in a reduced amount, indicating that PmrC was not the only enzyme that could be used to add PEtN to lipid A. Natural PEtN substitution was shown to be present in the lipid A of other serotypes of enterohaemorrhagic E. coli and absent from the lipid A of E. coli K-12. However, the cloned pmrC(O157) gene in a high-copy-number plasmid generated a large amount of PEtN-substituted lipid A species in E. coli K-12. The occurrence of PEtN-substituted lipid A species was associated with a slight increase in the MICs of cationic peptide antibiotics, suggesting that the lipid A modification with PEtN would be beneficial for survival of E. coli O157 : H7 in certain environmental niches. However, PEtN substitution in the lipid A profiles was not detected when putative inner-membrane proteins (YhbX/YbiP/YijP/Ecf3) that show significant similarity with PmrC in amino acid sequence were expressed from high-copy-number plasmids in E. coli K-12. This suggests that these potential homologues are not responsible for the addition of PEtN to lipid A in the pmrC mutant of E. coli O157 : H7. When cells were treated with EDTA, the amount of palmitoylated lipid A from the cells carrying a high-copy-number plasmid clone of pmrC(O157) that resulted in significant increase of PEtN substitution was unchanged compared with cells without PEtN substitution, suggesting that the PEtN moiety substituted in lipid A does not compensate for the loss of divalent cations required for bridging neighbouring lipid A molecules.
authors.affiliation: Departments of Laboratory Medicine and Pathobiology and Biochemistry, University of Toronto, 6213 Medical Sciences Building, 1 King's College Circle, Toronto, Ontario, Canada M5S 1A8.|Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
authors.forename: Sang-Hyun
authors.initials: SH
authors.lastname: Kim
authors.affiliation: Departments of Laboratory Medicine and Pathobiology and Biochemistry, University of Toronto, 6213 Medical Sciences Building, 1 King's College Circle, Toronto, Ontario, Canada M5S 1A8.
authors.forename: Wenyi
authors.initials: W
authors.lastname: Jia
authors.affiliation: Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
authors.forename: Valeria R
authors.initials: VR
authors.lastname: Parreira
authors.affiliation: Departments of Laboratory Medicine and Pathobiology and Biochemistry, University of Toronto, 6213 Medical Sciences Building, 1 King's College Circle, Toronto, Ontario, Canada M5S 1A8.
authors.forename: Russell E
authors.initials: RE
authors.lastname: Bishop
authors.affiliation: Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
authors.forename: Carlton L
authors.initials: CL
authors.lastname: Gyles
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D048168:Escherichia coli K12 / Q000201:enzymology / Q000235:genetics; D019453:Escherichia coli O157 / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D004983:Ethanolamines / Q000737:chemistry* / Q000378:metabolism; D008050:Lipid A / Q000737:chemistry*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D009154:Mutation; D011112:Polymyxin B / Q000031:analogs & derivatives / Q000494:pharmacology; D011113:Polymyxins / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D029968:Escherichia coli Proteins; D004983:Ethanolamines; D008050:Lipid A; D008565:Membrane Proteins; C510752:PmrC protein, E coli; D011113:Polymyxins; C005448:phosphorylethanolamine; C038934:polymyxin B nonapeptide; D011112:Polymyxin B