Structural analysis of a novel anionic polysaccharide from Porphyromonas gingivalis strain W50 related to Arg-gingipain glycans

Summary The Arg-gingipains (RgpsA and B) of Porphyromonas gingivalis are a family of extracellular cysteine pro- teases and are important virulence determinants of this periodontal bacterium. A monoclonal antibody, MAb1B5, which recognizes an epitope on glycosy- lated monomeric RgpAs also cross-reacts with a cell- surface polysaccharide of P. gingivalis W50 suggest- ing that the maturation pathway of the Arg-gingipains may be linked to the biosynthesis of a surface carbohydrate. We report the purification and struc- tural characterization of the cross-reacting anionic polysaccharide (APS), which is distinct from both the lipopolysaccharide and serotype capsule polysaccha- ride of P. gingivalis W50. The structure of APS was determined by 1D and 2D NMR spectroscopy and methylation analysis, which showed it to be a phos- phorylated branched mannan. The backbone is built up of α -1,6-linked mannose residues and the side- chains contain α -1,2-linked mannose oligosaccha- rides of different lengths (one to two sugar residues) attached to the backbone via 1,2-linkage. One of the side-chains in the repeating unit contains Man α α α 1-