title: Structural Elucidation of the O-Antigen Polysaccharide from Escherichia coli O181.
abstract: Shiga-toxin-producing Escherichia coli (STEC) is an important pathogen associated to food-borne infection in humans; strains of E. coli O181, isolated from human cases of diarrhea, have been classified as belonging to this pathotype. Herein, the structure of the O-antigen polysaccharide (PS) from E. coli O181 has been investigated. The sugar analysis showed quinovosamine (QuiN), glucosamine (GlcN), galactosamine (GalN), and glucose (Glc) as major components. Analysis of the high-resolution mass spectrum of the oligosaccharide (OS), obtained by dephosphorylation of the O-deacetylated PS with aqueous 48 % hydrofluoric acid, revealed a pentasaccharide composed of two QuiNAc, one GlcNAc, one GalNAc, and one Glc residue. The (1)H and (13)C NMR chemical shift assignments of the OS were carried out using 1 D and 2 D NMR experiments, and the OS was sequenced using a combination of tandem mass spectrometry (MS/MS) data and NMR (13)C NMR glycosylation shifts. The structure of the native PS was determined using NMR spectroscopy, and it consists of branched pentasaccharide repeating units joined by phosphodiester linkages: →4)[α-l-QuipNAc-(1→3)]-α-d-GalpNAc6Ac-(1→6)-α-d-Glcp-(1→P-4)-α-l-QuipNAc-(1→3)-β-d-GlcpNAc-(1→; the O-acetyl groups represent 0.4 equivalents per repeating unit. Both the OS and PSs exhibit rare conformational behavior since two of the five anomeric proton resonances could only be observed at an elevated temperature.
authors: Arrhenius Laboratory, Department of Organic Chemistry, Stockholm University S-106 91 Stockholm (Sweden).
authors: Carolina
authors: C
authors: Fontana
authors: Department of Laboratory Medicine, Division of Clinical Microbiology, Karolinska Institute, Karolinska University Hospital S-141 86 Stockholm (Sweden).
authors: Andrej
authors: A
authors: Weintraub
authors: Arrhenius Laboratory, Department of Organic Chemistry, Stockholm University S-106 91 Stockholm (Sweden).
authors: Göran
authors: G
authors: Widmalm
keywords: Escherichia coli; NMR spectroscopy; O-antigen; polysaccharides; structure elucidation