Open AccessConformational Preferences of the O-Antigen Polysaccharides of Escherichia coli O5ac and O5ab Using NMR Spectroscopy and Molecular Modeling
Author(s) -
Achyut Sarkar,
Carolina Fontana,
Anne Imberty,
Serge Pérez,
Göran Widmalm
Publication year - 2013
Publication title -
biomacromolecules
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.689
H-Index - 220
eISSN - 1526-4602
pISSN - 1525-7797
DOI - 10.1021/bm400354y
Subject(s) - escherichia coli , nuclear magnetic resonance spectroscopy , polysaccharide , chemistry , spectroscopy , biochemistry , stereochemistry , physics , quantum mechanics , gene
Escherichia coli serogroup O5 comprises two different subgroups (O5ab and O5ac), which are indiscernible from the point of view of standard immunological serotyping. The structural similarities between the O-antigen polysaccharides (PSs) of these two strains are remarkable, with the only difference being the glycosidic linkage connecting the biological tetrasaccharide repeating units. In the present study, a combination of NMR spectroscopy and molecular modeling methods were used to elucidate the conformational preferences of these two PSs. The NMR study was based on the analysis of intra- and inter-residue proton-proton distances using NOE build-up curves. Molecular models of the repeating units and their extension to polysaccharides were obtained, taking into account the conformational flexibility as assessed by the force field applied and a genetic algorithm. The agreements between experimentally measured and calculated distances could only be obtained by considering an averaging of several low energy conformations observed in the molecular models.