The structure of the O-antigen polysaccharide (PS) of Escherichia coli O115 has been investigated using a combination of component analysis together with 1D and 2D NMR spectroscopy experiments. The repeating unit of the O-antigen was elucidated using the O-deacetylated PS and has the following branched pentasaccharide structure: →3)[β-L-Rhap-(1→4)]-β-D-GlcpNAc-(1→4)-α-D-GalpA-(1→3)-α-D-Manp-(1→3)-β-D-GlcpNAc-(1→. Cross-peaks of low intensity, corresponding to a β-L-Rhap-(1→4)-β-D-GlcpNAc-(1→ structural element, were present in the NMR spectra and attributed to the terminal part of the polysaccharide; this information defines the biological repeating unit of the O-antigen by having a 3-substituted N-acetyl-d-glucosamine residue at its reducing end. Analysis of the NMR spectra of the native polysaccharide revealed O-acetyl groups distributed over different positions of the l-Rhap residue (~0.70 per repeating unit) as well as at O-2 and O-3 of the d-GalpA residue (~0.03 and ~0.25 per repeating unit, respectively), which is in agreement with the presence of two acetyltransferases previously identified in the O-antigen gene cluster (Wang et al. 2010). In addition, the four glycosyltransferases initially identified in the O-antigen gene cluster of E. coli O115 were analyzed using BLAST, and the function of two of them predicted based on similarities with glycosyltransferases from Shigella dysenteriae type 5 and 12, as well as Escherichia coli O58 and O152.
Lipopolysaccharide, NMR, structure, O-acetylation, O-antigen gene cluster, Escherichia coli O115
NCBI PubMed ID: 23193180Publication DOI: 10.1093/glycob/cws161Journal NLM ID: 9104124Publisher: IRL Press at Oxford University Press
Correspondence: G. Widmalm
Institutions: Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, Stockholm, Sweden
Methods: 13C NMR, 1H NMR, GLC-MS, NMR-2D, sugar analysis, GLC, de-O-acetylation, NMR-1D
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