title: Structural characterization of the lipid A component of Helicobacter pylori rough- and smooth-form lipopolysaccharides.
abstract: The chemical structure of free lipid A isolated from rough- and smooth-form lipopolysaccharides (R-LPS and S-LPS, respectively) of the human gastroduodenal pathogen Helicobacter pylori was elucidated by compositional and degradative analysis, nuclear magnetic resonance spectroscopy, and mass spectrometry. The predominant molecular species in both lipid A components are identical and tetraacylated, but a second molecular species which is hexaacylated is also present in lipid A from S-LPS. Despite differences in substitution by acyl chains, the hydrophilic backbone of the molecules consisted of beta(1,6)-linked D-glucosamine (GlcN) disaccharide 1-phosphate. Because of microheterogeneity, nonstoichiometric amounts of ethanolamine-phosphate were also linked to the glycosidic hydroxyl group. In S-LPS, but not in R-LPS, the hydroxyl group at position 4' was partially substituted by another phosphate group. Considerable variation in the distribution of fatty acids on the lipid A backbone was revealed by laser desorption mass spectrometry. In tetraacyl lipid A, the amino group of the reducing GlcN carried (R)-3-hydroxyoctadecanoic acid (position 2), that of the nonreducing GlcN carried (R)-3-(octadecanoyloxy)octadecanoic acid (position 2'), and ester-bound (R)-3-hydroxyhexadecanoic acid was attached at position 3. Hexaacyl lipid A had a similar substitution by fatty acids, but in addition, ester-bound (R)-3-(dodecanoyloxy)hexadecanoic acid or (R)-3(tetradecanoyloxy)hexadecanoic acid was attached at position 3'. The predominant absence of ester-bound 4'-phosphate and the presence of tetraacyl lipid A with fatty acids of 16 to 18 carbons in length differentiate H. pylori lipid A from that of other bacterial species and help explain the low endotoxic and biological activities of H. pylori LPS.
authors.affiliation: Department of Microbiology, University College, Galway, Ireland. anthony.moran@ucg.ie
authors.forename: A P
authors.initials: AP
authors.lastname: Moran
authors.forename: B
authors.initials: B
authors.lastname: Lindner
authors.forename: E J
authors.initials: EJ
authors.lastname: Walsh
mesh_terms: D019856:Ethanolamine / Q000032:analysis; D005227:Fatty Acids / Q000032:analysis / Q000737:chemistry; D005944:Glucosamine / Q000032:analysis; D016480:Helicobacter pylori / Q000737:chemistry*; D008050:Lipid A / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008745:Methylation; D009844:Oligosaccharides / Q000737:chemistry; D010710:Phosphates / Q000032:analysis
chemical_list: D005227:Fatty Acids; D008050:Lipid A; D009844:Oligosaccharides; D010710:Phosphates; D019856:Ethanolamine; D005944:Glucosamine