Determination of the structure of the lipid A fraction from the lipopolysaccharide of Pseudomonas cichorii by means of NMR and MALDI-TOF mass spectrometry

The chemical structure of lipid A from the lipopolysaccharide of the plant- associated bacterium Pseudomonas cichorii, was elucidated by compositional analysis and spectroscopic methods (MALDI-TOF and 2D NMR). The lipid A fraction showed remarkable heterogeneity with respect to the fatty acid and phosphate composition. The major species are hexaacylated and pentaacylated lipid A, bearing the (R)-3-hydroxydodecanoic acid [C12:0 (3OH)] in amide linkage and an (R)-3-hydroxydecanoic [C10:0 (3OH)] in ester linkage while the secondary fatty acids are present as C12:0 and C12:0 (2-OH). A nonstoichiometric phosphate substitution at position C-4' of the distal GlcN was detected. Interestingly, the pentaacyl lipid A is lacking a primary fatty acid, namely the C10:0 (3-OH) at position C-3'. A potential biological meaning of this peculiar lipid A is also suggested.