Structural characterization of lipid A from nontypeable and type f Haemophilus influenzae: variability of fatty acid substitution.

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.