STRUCTURAL ELUCIDATION OF THE BACKBONE OLIGOSACCHARIDE FROM THE LIPOPOLYSACCHARIDE OF MORAXELLA-CATARRHALIS SEROTYPE-A

The cell-surface lipopolysaccharide produced by Moraxella catarrhalis serotype A is composed of a hydrophobic lipid A moiety and an oligosac charide, but lacks high-molecular-weight O-polysaccharide chains. The oligosaccharide component is composed of D-glucose, D-galactose, D-glu cosamine, and 3-deoxy-D-manno-octulosonic acid. The carbohydrate backb one was obtained from the lipopolysaccharide by employing a reaction s equence involving deacylation, dephosphorylation, and reduction of the reducing D-glucosamine terminus of the lipid A moiety. Structural ana lysis of the backbone oligosaccharide employed a combination of microa nalytical methods and nuclear magnetic resonance spectroscopy. Homo- a nd hetero-nuclear chemical shift correlation techniques and nuclear Ov erhauser enhancement (NOE) experiments led to the unambiguous assignme nt of the H-1 and C-13 resonances associated with each of the componen t glycosyl residues and established their sequence within the backbone oligosaccharide as shown, [GRAPHICS] This lipopolysaccharide was foun d to consist of a highly branched, D-glucose-containing inner-core reg ion which possesses a unique and unusual solution conformation. This w as established by measurement of transglycosidic NOEs and three-bond H -1-C-13 coupling constants, in conjunction with molecular modeling. A D-galactose-containing disaccharide identified as a terminal group of the lipopolysaccharide was structurally identical to antigenic epitope s expressed by certain mammalian epithelial cells and may be related t o the virulence potential of this human pathogen.