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The Structure of Aerobacter aerogenes Capsular Polysaccharide

From the ¹ From the Department of Physiological Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205

A capsular polysaccharide produced by Aerobacter aerogenes has been purified and shown to consist of galactose, mannose, and glucuronic acid in a molar ratio of 2:1:1, respectively. Partial acid hydrolysis liberated an aldobiouronic acid identified as 2-O-ß-d-glucuronosyl-d-mannose. Analysis of capsular polysaccharide by Smith periodate degradation further indicated that all of the galactose residues are linked through C-3, all of the mannose residues are linked through both C-2 and C-3, and all of the glucuronic acid is at terminal, nonreducing positions.

Digestion of capsular polysaccharide with a specific phage-induced polysaccharide depolymerase resulted in its nearly quantitative conversion to two limit oligosaccharides, termed A and B. Partial acid hydrolysis, methylation analysis, and periodate degradation indicated that A is the tetrasaccharide, Gal-1 3-(GlcUA-1 2)-Man-1 3-Gal. B was characterized as an octasaccharide composed of two units of A by the following procedure: Smith periodate degradation of B yielded the pentasaccharide mannosyl ()/ galactosyl ()/ galactosyl ()/ mannosyl ()/ lyxitol. This pentasaccharide was characterized and the anomeric configuration of the glycosidic bonds determined by sequential enzymatic degradation with specific exoglycosidases. Further analyses indicated that B is the octasaccharide, Gal-1 ()/ 3-(GlcUA-1 (ß)/ 2)-Man-1 ()/ -3-Gal-1 ()/ 3-Gal-1 ()/ 3-(GlcUA-1 (ß)/ 2)-Man-1 ()/ 3-Gal.

A third oligosaccharide, termed C, was present in small amounts in extensive depolymerase digests of capsular polysaccharide. This oligosaccharide was shown to be a dodecasaccharide composed of three units of A. Exhaustive depolymerase digestion of C resulted in its slow degradation to yield equimolar amounts of A and B.

These results indicate that Aerobacter aerogenes capsular polysaccharide is composed of repeating sequences of the following tetrasaccharide.

[see PDF for sequence]

Moreover, they also indicate that the phage-induced polysaccharide depolymerase is a glycanohydrolase which specifically cleaves the galactosyl-1 ()/ 3-galactose linkages in the capsular polysaccharide.

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