Chemical Structure and Immunological Specificity of the Streptococcal Group E Cell Wall Polysaccharide Antigen

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The streptococcal group E cell wall polysaccharide antigen was extracted from strain K129 cells with hot trichloroacetic acid and purified. It contained rhamnose and glucose in a 2:1 molar ratio, 2% protein, 1% phosphorus, and was free of muramic acid and glycerol. No type polysaccharide antigen was present. The reaction of specific group E rabbit antiserum with the polysaccharide was effectively inhibited by d-glucose and β-glucosides such as 1-methyl-β-d-glucose, cellobiose, and gentiobiose. The 1-methyl-α-d-glucose was one-half as effective as the beta isomer. l-Rhamnose and N-acetyl-d-glucosamine were ineffective. Partial acid hydrolysis of the antigen followed by chromatographic separation of the oligosaccharides resulted in the isolation and analysis of five fractions. These fractions were di-, tri-, and tetrasaccharides. A study of these fractions by chemical analysis, reduction with borohydride, inhibition of the antigen-antibody reaction, release of glucose by β-glucosidase, and other evidence indicate that β-d-glucose is the immunodominant sugar in the antigen. A glucose-rhamnose trisaccharide (1:2 molar ratio) was the most effective inhibitor of the precipitin reaction; the glucose was readily released by β-glucosidase, and one-half of the rhamnose was reduced with borohydride. This trisaccharide is considered to be a repeating unit in the native polysaccharide and probably has the following structure: O-β-d-glucosyl-(1-2)-O-α-l-rhamnosyl- (1-4)-l-rhamnose. A glucose-rhamnose disaccharide in which the hexose and pentose are linked as in the trisaccharide was an effective inhibitor of the precipitin reaction. Strain K129 cells do not appear to contain a type polysaccharide antigen.

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