Structural Investigations on a Cell-Wall Lipopolysaccharide from Neisseria sicca

Abstract

Lipopolysaccharide (LPS) prepared from Neisseria sicca in 1.5% yield contained D-glucose, D-glucosamine, D-galactosamine, 3-deoxyoctulosonic acid, protein, lipid A, and phosphate. The molecule was judged to be homogeneous as tested by free boundary electrophoresis. D-Galactosamine was associated exclusively with the polysaccharide portion of the molecule and was in fourfold excess of D-glucosamine. The latter hexosamine was primarily a constituent of the lipid A moiety in which it formed the backbone structure linked glycosidically 1 → 4. To this structure, fatty acids, principally β-hydroxymyristic acid and β-hydroxylauric acid, were linked along with phosphate groups. The D-glucosamine units in the polysaccharide portion of the LPS molecule were also attached by 1 → 4 glycosidic linkages. D-Galactosamine units did not survive the methylation procedures due presumably to the lack of acyl protecting groups on its amino groups. Methylation results showed that approximately one-third of the D-glucose units were nonreducing end groups, approximately one-third were linked α1 → 2, a small proportion was linked 1 → 4, and the remainder was branched through C-3, C-4, and C-6. Periodate oxidation results were in agreement with the structure proposed on the basis of the methylation data. The LPS of N. sicca was considerably simpler than that of N. perflava and lacked heptose, rhamnose, and ethanolamine components.