Structural elucidation of the novel type VII group B Streptococcus capsular polysaccharide by high resolution NMR spectroscopy

The type VII capsular polysaccharide isolated from the newly discovered group B Streptococcus (GBS) strain contains d-glucose, d-galactose, N-acetyl-d-glucosamine and N-acetylneuraminic acid in the molar ratio 2:2:1:1. High-resolution one- and two-dimensional (1D and 2D) 1H and 13C NMR spectroscopy of the native and desialylated polysaccharides showed the type VII GBS capsular polysaccharide to contain the following branched hexasaccharide repeating unit: → 4)βdGlc(1 → 4)αdGlc(1 → 4)βdGal(1 →6↑|αNeu5Ac(2 → 3)βdGal(1 → 4)βz.sbnd;dGlcNac Despite extensive structural similarity with the previously described GBS polysaccharides, the type VII polysaccharide showed no cross-reaction with the heterologous antisera.