title: Conformational studies of the O-specific polysaccharide of Shigella flexneri 5a and of four related synthetic pentasaccharide fragments using NMR and molecular modeling.
abstract: As part of a program for the development of synthetic vaccines against the pathogen Shigella flexneri, we used a combination of NMR and molecular modeling methods to study the conformations of the O-specific polysaccharide (O-SP) of S. flexneri 5a and of four related synthetic pentasaccharide fragments. The NMR study, based on the analysis of 1H and 13C chemical shifts, the evaluation of inter-residue distances, and the measurement of one- and three-bond heteronuclear coupling constants, showed that the conformation of one of the four pentasaccharides is similar to that of the native O-SP in solution. Interestingly, inhibition enzyme-linked immunosorbent assay demonstrated that a protective monoclonal antibody specific for S. flexneri 5a has a greater affinity for this pentasaccharide than for the others. We carried out a complete conformational search on the pentasaccharides using the CICADA algorithm interfaced with MM3 force field. We calculated Boltzmann-averaged inter-residue distances and 3JC,H coupling constants for the different conformational families and compared the results with NMR data for all pentasaccharides. Our experimental data are consistent with only one conformational family. We also used molecular modeling data to build models of the O-SP with the molecular builder program POLYS. The models that are in agreement with NMR data adopt right-handed 3-fold helical structures in which the branched glucosyl residue points outwards.
authors.affiliation: Unité de RMN des Biomolécules, URA CNRS 2185, Institut Pasteur, 28 rue du Dr Roux, 75724 Paris, Cedex 15, France.
authors.forename: Marie-Jeanne
authors.initials: MJ
authors.lastname: Clément
authors.forename: Anne
authors.initials: A
authors.lastname: Imberty
authors.forename: Armelle
authors.initials: A
authors.lastname: Phalipon
authors.forename: Serge
authors.initials: S
authors.lastname: Pérez
authors.forename: Catherine
authors.initials: C
authors.lastname: Simenel
authors.forename: Laurence A
authors.initials: LA
authors.lastname: Mulard
authors.forename: Muriel
authors.initials: M
authors.lastname: Delepierre
mesh_terms: D000465:Algorithms; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D019081:O Antigens / Q000737:chemistry* / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry*; D011522:Protons; D012763:Shigella flexneri / Q000378:metabolism*
chemical_list: D019081:O Antigens; D011134:Polysaccharides; D011522:Protons