Complete structure of the adhesin receptor polysaccharide of Streptococcus oralis ATCC 55229 (Streptococcus sanguis H1)

Abstract

This report describes the determination of the complete primary structure of the adhesin receptor polysaccharide of Streptococcus oralis ATCC 55229 (previously characterized as Streptococcus sanguis H1), a Gram-positive bacteria implicated in dental plaque formation. The polysaccharide was isolated from S. oralis ATCC 55229 cells after deproteination, enzymatic hydrolysis, and ion exchange chromatography. It was shown to consist of rhamnose, galactose, glucose, glycerol, and phosphate, in molar ratios of 2:3:1:1:1. Sequence and linkage assignments of the glycosyl residues were obtained by methylation analysis followed by gas-liquid chromatography and electron-impact mass spectrometry. 31P NMR spectroscopy revealed that phosphate was present in a diester, connecting glycerol to one of the galactosyl residues. High-performance liquid chromatography of a partial acid hydrolysate of the polysaccharide confirmed this finding by showing galactose 6-phosphate and glycerol 1-phosphate. The structural determination was completed by the combination of two-dimensional homonuclear Hartmann-Hahn and NOE experiments and heteronuclear [1H,13C] and [1H,31P] multiple-quantum coherence experiments. Thus, the adhesin receptor polysaccharide of S. oralis ATCC 55229 was found to be a polymer composed of hexasaccharide repeating units that contain glycerol linked through a phosphodiester to C6 of the alpha-galactopyranosyl residue and are joined end-to-end through galactofuranosyl-beta(1-->3)-rhamnopyranosyl linkages: [formula: see text] This structure is novel among bacterial cell surface polysaccharides in general and specifically among those implicated in dental plaque formation.