The structure of the O-antigen polysaccharide (PS) from Escherichia coli O42 has been investigated by NMR spectroscopy as the main method, which was complemented with sugar analysis, mass spectrometry, and analysis of biosynthetic information. The O-specific chain of the O-deacylated lipopolysaccharide (LPS-OH) consists of branched tetrasaccharide-glycerol repeating units joined by phosphodiester linkages. The lipid-free polysaccharide contains 0.8equiv of O-acetyl groups per repeating unit and has the following teichoic acid-like structure: Based on biosynthetic aspects, this should also be the biological repeating unit. This O-antigen structure is remarkably similar to that of E. coli O28ac, differing only in the presence or absence, respectively, of a glucose residue at the branching point. The structural similarity explains the serological cross-reactivity observed between strains of these two serogroups, and also their almost identical O-antigen gene cluster sequences.
NMR, O-antigen, Escherichia coli, O-acetylation
NCBI PubMed ID: 24909379Publication DOI: 10.1016/j.carres.2014.05.003Journal NLM ID: 0043535Publisher: Elsevier
Correspondence: G. Widmalm
Institutions: Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, Stockholm, Sweden
Methods: 13C NMR, 1H NMR, NMR-2D, HF solvolysis, de-O-acylation, sugar analysis, 31P NMR, ESI-MS, acid hydrolysis, GLC, NMR-1D
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