Abstract
The specific capsular polysaccharides of Streptococcuspneumoniae types 19B and 19C (American types 58 and 59) were investigated by a combination of 1H, 13C, and 31P nuclear magnetic resonance spectroscopy and analytical methods based on mass spectrometry. The two polysaccharides were found to be high molecular weight polymers composed of L-rhamnose, 2-amino-2-deoxy-D-mannose, D-ribose, D-glucose, and phosphate. Homo- and heteronuclear chemical shift correlation techniques and nuclear Overhauser enhancement experiments led to the unambiguous assignment of the 1H and 13C resonances from the glycose residues and established their sequence within repeating oligosaccharide units. The oligosaccharide units are polymerized through phosphate diester linkages.[Formula: see text]Both polysaccharides share a common hexasaccharide structural unit and they differ only in the degree of substitution at the branched 2-acetamido-2-deoxy-β-D-mannopyranosyl residue: the 19C polysaccharide is O-6 linked by β-D-glucopyranosyl end groups to form a heptasaccharide repeating unit, while the 19B polysaccharide is unsubstituted at that position. The serologic cross-reactivity between S. pneumoniae serotypes 19B and 19C can now be related to the structural similarity of the antigenic capsular polysaccharides. Keywords: Streptococcuspneumoniae, capsular polysaccharide, immuno chemistry.
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