Structural and Immunochemical Characterization of the Lipooligosaccharides Expressed by Neisseria subflava 44

Neisserial lipooligosaccharides (LOSs) are a family of complex cell surface glycolipids. We used mass spectrometry techniques (electrospray ionization, collision-induced dissociation, and multiple step), combined with fluorophore-assisted carbohydrate electrophoresis monosaccharide composition analysis, to determine the structure of the two low-molecular-mass LOS molecules (LOSI and LOSII) expressed by Neisseria subflava 44. We determined that LOSI contains one glucose on both the α and β chains. LOSII is structurally related to LOSI and differs from it by the addition of a hexose (either glucose or galactose) on the α chain. LOSI and LOSII were able to bind monoclonal antibody (MAb) 25-1-LC1 when analyzed by Western blotting experiments. We used a set of genetically defined Neisseria gonorrhoeae mutants that expressed single defined LOS epitopes and a group of Neisseria meningitidis strains that expresses chemically defined LOS components to determine the structures recognized by MAb 25-1-LC1. We found that extensions onto the β-chain glucose of LOSI block the recognition by this MAb, as does further elongation from the LOSII α chain. The LOSI structure was determined to be the minimum structure that is recognized by MAb 25-1-LC1.