THE CELL-WALL POLYSACCHARIDE OF STREPTOCOCCUS-GORDONII-38 - STRUCTUREAND IMMUNOCHEMICAL COMPARISON WITH THE RECEPTOR POLYSACCHARIDES OF STREPTOCOCCUS-ORALIS-34 AND STREPTOCOCCUS-MITIS J22

As part of our ongoing investigations involving lectin-mediated adhesi on among oral bacteria, the receptor polysaccharide from Streptococcus gordonii 38 was isolated and characterized. Carbohydrate analysis of the hydrolysed; S. gordonii 38 polysaccharide by high-performance anio n-exchange chromatography with pulsed amperometric detection (HPAEC-PA D) showed galactose (Gal) (2 mel), N-acetylgalactosamine (GalNAc) (1 m el), rhamnose (Rha) (2 mel), glucose (Glc) (1 mel) and galactosamine-6 -phosphate (1 mol). Mild acid hydrolysis of the polysaccharide yielded a heptasaccharide repeating unit, The structure of the heptasaccharid e repeating unit was determined by high-resolution NMR spectroscopy wh ich includes various homonuclear (DQF-COSY, TQF-COSY, NOESY and HOHAHA ) and heteronuclear experiments (HMQC), including linkage assignments by H-1-C-13 long-range correlation (HMBC). Complete H-1 and C-13 NMR a ssignments for the intact polysaccharide yielded the covalent structur e of a heptasaccharide repeating unit: [-->6)Gal(p)NAc alpha(1-->3)-Rh a(p) beta-(1-->4)-Glc(p) beta-(1-->6)-Gal(f) beta-(1-->6)- Rha(p) alph a-(1-->2)-NE arrow Gal(p)NAc beta-(1-->3)-Gal(p) alpha-(1-->PO4--](n) The structure of the strain 38 polysaccharide is closely related to th ose of Streptococcus mitis J22 and Streptococcus oralis 34. Thus, the difference between the strain 38 and J22 heptasaccharides was at their reducing ends, with GalNAc beta-(1-->3)-Gal in the former and Gal bet a-(1-->3)-GalNAc in the latter, while the difference between the 38 he ptasaccharide and 34 hexasaccharide was at the non-reducing ends, wher e a rhamnose branch occurred in the former but not the latter structur e. When compared by their quantitative precipitin curves with rabbit a ntibodies against each streptococcal strain, the strain 38 polysacchar ide reacted more like the polysaccharide of strain J22 than that of st rain 34. In contrast, each strain was recognized by the Gal- and GalNA c-reactive lectins of Actinomyces spp., but only strains 38 and 34 wer e recognized by GalNAc-sensitive lectins of other streptococci. These findings strongly support the hypothesis that the immunogenic features of these polysaccharides are distinct from those detected by lectin b inding.