Structural analysis of the polysaccharide from the lipopolysaccharide of Porphyromonas gingivalis strain W50

The lipopolysaccharide (LPS) of Porphyromonas gingivalis is an important pro-inflammatory molecule in periodontal disease and a significant target of the host's specific immune response. In addition, we recently demonstrated using monoclonal antibodies that the Arg-gingipains of P. gingivalis are post-translationally modified with glycan chains that are immunologically related - to an LPS preparation from this organism. In the present investigation, we determined the structure of the O-polysaccharide of P. gingivalis W50 that was fully characterized on the basis of 1D and 2D NMR (DQF-COSY, TOCSY, NOESY, ROESY, H-1-C-13 HSQC and H-1-P-31 HXTOCSY) and GC-MS data. These data allowed us to conclude that the O-polysaccharide is built up of the tetrasaccharide repeating sequence: -->6)-alpha -D-Glcp-(1-->4)-alpha -L-Rhap-(1-->3)-beta -D-GalNAc-(1-->3)-alpha -D-Galp-(1--> and carries a monophosphoethanolamine residue at position C-2 of the alpha -rhamnose residue in a nonstoichiometric (approximately 60%) amount. These data indicate that the O-polysaccharide of P. gingivalis LPS is composed of an unusually modified tetrasaccharide repeating unit.