Chemical modification and serological properties of the 3-deoxy-alpha-D-manno-2-octulosonic acid-containing polysaccharide from Escherichia coli LP1092.

The alpha-D configuration of the 3-deoxy-D-manno-2-octulosylonic acid residues in the E. coli LP1092 polysaccharide was definitively assigned by a comparison of its c.d. spectrum with those of methyl 3-deoxy-alpha- and -beta-D-manno-2-octulopyranosidonic acid. The c.d. spectrum of the polysaccharide showed a negative n----pi transition at 211 nm, associated with carboxyl groups, which correlated well with the negative band at 218 nm exhibited in the c.d. spectrum of the methyl alpha-D-glycoside. In contrast, the methyl beta-D-glycoside gave a positive band in the same region of its c.d. spectrum, at 221 nm. Treatment of the E. coli LP1092 polysaccharide with 3-(3-dimethylaminopropyl)-1-ethylcarbodiimide hydrochloride yielded a modified polysaccharide containing O-acylisourea groups and intramolecular lactones, in addition to some unesterified carboxyl groups. Both forms of ester could be reduced to hydroxymethyl groups by sodium borohydride. Although immuno-precipitation of an antiserum specific for the E. coli LP1092 polysaccharide is not sensitive to the introduction of O-acylisourea groups into the polysaccharide, precipitation was completely eliminated when approximately half of the carboxyl groups of the polysaccharide were converted either into lactone or hydroxymethyl groups. Failure to precipitate the antiserum can be attributed to significant conformational changes in the polysaccharide brought about by the introduction of the latter two groups.