摘要：

The O-antigenic polysaccharide of theCE3 lipopolysaccharide (LPS) was structurally characterized using chemical degradations (Smith degradation and β-elimination of uronosyl residues) in combination with alkylation analysis, electrospray, and matrix-assisted laser desorption ionization-time of flight mass spectrometry, tandem mass spectrometry, and H COSY and TOCSY nuclear magnetic resonance spectroscopy analyses of the native polysaccharide and the derived oligosaccharides. The polysaccharide was found to be a unique, relatively low molecular weight glycan having a fairly discrete size, with surprisingly little variation in the number of repeating units (degree of polymerization = 5). The polysaccharide is-acetylated and contains a variety of-methylated glycosyl residues, rendering the native glycan somewhat hydrophobic. The molecular mass of the major de--acetylated species, including the reducing end 3-deoxy---2-octulosonic acid (Kdo) residue, is 3330 Da. The polysaccharide is comprised of a trisaccharide repeating unit having the structure →4)-α--GlcA-(1→4)-[α-3--Me-6-deoxy-Tal-(1→3)]-α--Fuc-(1→. The nonreducing end of the glycan is terminated with the capping sequence α-2,3,4-tri--Me-Fuc-(1→4)-α--GlcA-(1→, and the reducing end of the molecule consists of the non-repeating sequence →3)-α--Fuc-(1→3)-β--Man-(1→3)-β-QuiNAc-(1→4)-α-Kdo-(2→, where QuiNAc is -acetylquinovosamine (2--acetamido-2,6-dideoxyglucose). The reducing end Kdo residue links the O-chain polysaccharide to the core region oligosaccharide, resulting in a unique location for a Kdo residue in LPS, removed four residues distally from the lipid A moiety. Structural heterogeneity in the O-chain arises mainly from the-acetyl and -methyl substitution. Methylation analysis using trideuteriomethyl iodide indicates that a portion of the 2,3,4-tri--methylfucosyl capping residues, typically 15%, are replaced with 2--methyl- and/or 2,3-di-O-methylfucosyl residues. In addition, approximately 25% of the 3,4-linked branching fucosyl residues and 10% of the 3-linked fucosyl residues are 2--methylated. A majority of the glucuronosyl residues are methyl-esterified at C-6. These unique structural features may be significant in the infection process.

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