title: Structural study on the free lipid A isolated from lipopolysaccharide of Porphyromonas gingivalis.
abstract: The chemical structure of lipid A isolated from Porphyromonas gingivalis lipopolysaccharide was elucidated by compositional analysis, mass spectrometry, and nuclear magnetic resonance spectroscopy. The hydrophilic backbone of free lipid A was found to consisted of beta(1,6)-linked D-glucosamine disaccharide 1-phosphate. (R)-3-Hydroxy-15-methylhexadecanoic acid and (R)-3-hydroxyhexadecanoic acid are attached at positions 2 and 3 of the reducing terminal residue, respectively, and positions 2' and 3' of the nonreducing terminal unit are acylated with (R)-3-O-(hexadecanoyl)-15-methylhexadecanoic acid and (R)-3-hydroxy-13-methyltetradecanoic acid, respectively. The hydroxyl group at position 4' is partially replaced by another phosphate group, and the hydroxyl groups at positions 4 and 6' are unsubstituted. Considerable heterogeneity in the fatty acid chain length and the degree of acylation and phosphorylation was detected by liquid secondary ion-mass spectrometry (LSI-MS). A significant pseudomolecular ion of lipid A at m/z 1,769.6 [M-H]- corresponding to a diphosphorylated GlcN backbone bearing five acyl groups described above was detected in the negative mode of LSI-MS. Predominant ions, however, were observed at m/z 1,434.9 [M-H]- and m/z 1,449.0 [M-H]-, each representing monophosphoryl lipid A lacking (R)-3-hydroxyhexadecanoic and (R)-3-hydroxy-13-methyltetradecanoic acids, respectively. The presence of mono- and diphosphorylated lipid A species was also confirmed by LSI-MS of de-O-acylated lipid A (m/z 955.3 and 1,035.2, respectively).
authors.affiliation: Department of Oral Microbiology, Kanagawa Dental College, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Kumada
authors.forename: Y
authors.initials: Y
authors.lastname: Haishima
authors.forename: T
authors.initials: T
authors.lastname: Umemoto
authors.forename: K
authors.initials: K
authors.lastname: Tanamoto
mesh_terms: D002240:Carbohydrate Sequence; D005227:Fatty Acids / Q000737:chemistry; D006900:Hydroxylation; D008050:Lipid A / Q000737:chemistry* / Q000302:isolation & purification; D008070:Lipopolysaccharides / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010710:Phosphates / Q000737:chemistry; D016966:Porphyromonas gingivalis / Q000737:chemistry*; D016339:Spectrometry, Mass, Fast Atom Bombardment
chemical_list: D005227:Fatty Acids; D008050:Lipid A; D008070:Lipopolysaccharides; D010710:Phosphates