Chemical Structure of Lipid A Isolated from Flavobacterium meningosepticum Lipopolysaccharide

The chemical structure of the lipid A of the lipopolysaccharide component isolated from Flavobacterium meningosepticum IFO 12535 was elucidated. Methylation and nuclear magnetic resonance analyses showed that two kinds of hydrophilic backbone exist in the free lipid A: a β (1→6)-linked 2-amino-2-deoxy-d-glucose, which is usually present in enterobacterial lipid A’s, and a 2-amino-6-O-(2,3-diamino-2,3-dideoxy-β-d-glucopyranosyl)-2-deoxy-d-glucose, in a molar ratio of 1.00:0.35. Both backbones were α-glycosidically phosphorylated in position 1, and the hydroxyl groups at positions 4, 4′, and 6′ were unsubstituted. Liquid secondary ion-mass spectrometry revealed a pseudomolecular ion at m/z 1673 [M-H](−) as a major monophosphoryl lipid A component carrying five acyl groups. Fatty acid analysis showed that the lipid A contained 1 mol each of amide-linked (R)-3-OH iC(17:0), ester-linked (R)-3-OH iC(15:0), amide-linked (R)-3-O-(iC(15:0))-iC(17:0), and both amide- and ester-linked (R)-3-OH C(16:0). Fatty acid distribution analyses using several mass spectrometry determinations demonstrated that the former two constituents were distributed on positions 2 and 3 of the reducing terminal unit of the backbones and that the latter two were attached to the 2′ and 3′ positions in the nonreducing terminal residue.