Complete structure of the polysaccharide from Streptococcus sanguis J22.

The cell wall polysaccharides of certain oral streptococci such as Streptococcus sanguis strains 34 and J22, although immunologically distinct, act as receptors for the fimbrial lectins of Actinomyces viscosus T14V. We report the complete covalent structure of the polysaccharide from S. sanguis J22 which is composed of a heptasaccharide subunit linked by phosphodiester bonds. The repeating subunit, which contains alpha-GalNAc, alpha-rhamnose, beta-rhamnose, beta-glucose, and beta-galactose all in the pyranoside form and beta-galactofuranose, is compared with the previously published structure of the polysaccharide from strain 34. The structure has been determined almost exclusively by high-resolution nuclear magnetic resonance methods. The 1H and 13C NMR spectra of the polysaccharides from both strains 34 and J22 have been completely assigned. The stereochemistry of pyranosides was assigned from JH-H values determined from phase-sensitive COSY spectra, and acetamido sugars were assigned by correlation of the resonances of the amide 1H with the sugar ring protons. The 13C spectra were assigned by 1H-detected multiple-quantum correlation (HMQC) spectra, and the assignments were confirmed by 1H-detected multiple-bond correlation (HMBC) spectra. The positions of the glycosidic linkages were assigned by detection of three-bond 1H-13C correlation across the glycosidic linkage in the HMBC spectra. The positions of the phosphodiester linkages were determined by splittings observed in the 13C resonances due to 31P coupling and also by 1H-detected 31P correlation spectroscopy.