title: NMR reinvestigation of two N-acetylneuraminic acid-containing O-specific polysaccharides (O56 and O24) of Escherichia coli.
abstract: Structures for the N-acetylneuraminic acid (Neu5Ac)-containing O56 and O24 polysaccharides of Escherichia coli have been reported previously. During these studies unusual chemical shifts had been observed for the NMR signals for H-3eq and C-3 of the Neu5Ac residues of both polysaccharides. In further pursuing this phenomenon, we have reinvestigated the O56 and O24 polysaccharides as well as derived oligosaccharides by one- and two-dimensional NMR spectroscopy. The results showed that structures of both polysaccharides (PSs) had to be modified and formulated as [formula: see text] 2D ROESY spectra revealed a strong NOE between H-3eq of Neu5Ac and the protons of the side-chain sugar (H-3 and H-5 of alpha-D-Gal p in the O56 PS and H-3 of alpha-D-Glc p in the O24 PS) and also between H-3ax of Neu5Ac and H-3 of beta-D-Glc p in the main chain. This indicated a close spatial association of the seven-linked alpha-Neu5Ac and the side-chain residues alpha-D-Gal p (O56 PS) and alpha-D-Glc p (O25 PS), respectively. The strong long-range spatial contacts caused the unusual chemical shifts of H-3eq and C-3 of Neu5Ac.
authors.affiliation: Max-Planck-Institut für Immunbiologie, Freiburg, Germany.
authors.forename: V I
authors.initials: VI
authors.lastname: Torgov
authors.forename: A S
authors.initials: AS
authors.lastname: Shashkov
authors.forename: B
authors.initials: B
authors.lastname: Jann
authors.forename: K
authors.initials: K
authors.lastname: Jann
mesh_terms: D000116:Acetylgalactosamine / Q000032:analysis; D000117:Acetylglucosamine / Q000032:analysis; D002240:Carbohydrate Sequence; D004926:Escherichia coli / Q000737:chemistry* / Q000276:immunology; D005690:Galactose / Q000032:analysis; D005947:Glucose / Q000032:analysis; D008070:Lipopolysaccharides / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009005:Monosaccharides / Q000032:analysis; D019158:N-Acetylneuraminic Acid; D019081:O Antigens; D011135:Polysaccharides, Bacterial / Q000737:chemistry* / Q000302:isolation & purification; D012794:Sialic Acids / Q000032:analysis*
chemical_list: D008070:Lipopolysaccharides; D009005:Monosaccharides; D019081:O Antigens; D011135:Polysaccharides, Bacterial; D012794:Sialic Acids; D019158:N-Acetylneuraminic Acid; D005947:Glucose; D000116:Acetylgalactosamine; D000117:Acetylglucosamine; D005690:Galactose