title: Structural characterization of lipid A from nontypeable and type f Haemophilus influenzae: variability of fatty acid substitution.
abstract: Lipid A isolated by mild acid hydrolysis from lipopolysaccharides of 22 nontypeable and 2 type f Haemophilus influenzae strains was investigated using electrospray ionization coupled to quadrupole ion trap mass spectrometry. The lengths, positions, and number of acyl chains in the lipid A molecule were determined using multiple-step tandem mass spectrometry (MSn). All of the analyzed strains showed a major lipid A molecule comprising beta-2-amino-2-deoxy-D-glucopyranose-(1-->6)-alpha-2-amino-2-deoxy-D-glucopyranose phosphorylated at the C4' and C1 positions. The C2/C2' and C3/C3' positions were substituted by amide-linked and ester-linked 3-hydroxytetradecanoic acid chains, respectively. The fatty acid chains on C3' and C2' were further esterified by tetradecanoic acid chains. In all strains, minor amounts of lipid A molecules with different acylation patterns were identified. Thus, structures comprising the hexaacylated lipid A with the C2 or C3 position being substituted by 3-hydroxydecanoic acid, and hexaacylated lipid A with the C3 and C3' positions being substituted by 3-hydroxydodecanoic or dodecanoyloxytetradecanoic acid, respectively, were found. In addition, lipid A with an acetyl group attached to the 3-hydroxytetradecanoic acid groups attached to the C2 or C3 position was detected in two nontypeable H. influenzae strains.
authors.affiliation: Clinical Research Centre, Karolinska Institutet and University College of South Stockholm, NOVUM, S-141 86 Huddinge, Sweden.
authors.forename: Ivan
authors.initials: I
authors.lastname: Mikhail
authors.forename: Håkan H
authors.initials: HH
authors.lastname: Yildirim
authors.forename: Emma C H
authors.initials: EC
authors.lastname: Lindahl
authors.forename: Elke K H
authors.initials: EK
authors.lastname: Schweda
mesh_terms: D005227:Fatty Acids / Q000032:analysis; D006193:Haemophilus influenzae / Q000737:chemistry* / Q000145:classification; D008050:Lipid A / Q000737:chemistry*; D013058:Mass Spectrometry / Q000379:methods; D012680:Sensitivity and Specificity; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D005227:Fatty Acids; D008050:Lipid A