The Structure of Aerobacter aerogenes Capsular Polysaccharide

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 -β- 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 (α)/→ galactosyl (α)/→ galactosyl (α)/→ mannosyl (α)/→ 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 (α)/→ 3-(GlcUA-1 (β)/→ 2)-Man-1 (α)/→ -3-Gal-1 (α)/→ 3-Gal-1 (α)/→ 3-(GlcUA-1 (β)/→ 2)-Man-1 (α)/→ 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 (α)/→ 3-galactose linkages in the capsular polysaccharide.