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  • 1.
    Blasco, Pilar
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Patel, Dhilon S.
    Engström, Olof
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Im, Wonpil
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Conformational Dynamics of the Lipopolysaccharide from Escherichia coli O91 Revealed by Nuclear Magnetic Resonance Spectroscopy and Molecular Simulations2017In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 56, no 29, p. 3826-3839Article in journal (Refereed)
    Abstract [en]

    The outer leaflet of the outer membrane in Gram-negative bacteria contains lipopolysaccharides (LPS) as a major component, and the outer membrane provides a physical barrier and protection against hostile environments. The enterohemorrhagic Escherichia coli of serogroup O91 has an O-antigen polysaccharide (PS) with five sugar residues in the repeating unit (RU), and the herein studied O-antigen PS contains similar to 10 RUs. H-1-C-13 HSQC-NOESY experiments on a 1-C-13-labeled PS were employed to deduce H-1-H-1 cross-relaxation rates and transglycosidic (3)J(CH) related to the psi torsional angles were obtained by H-1-H-1 NOESY experiments. Dynamical parameters were calculated from the molecular dynamics (MD) simulations of the PS in solution and compared to those from C-13 nuclear magnetic resonance (NMR) relaxation studies. Importantly, the MD simulations can reproduce the dynamical behavior of internal correlation times along the PS chain. Two-dimensional free energy surfaces of glycosidic torsion angles delineate the conformational space available to the O-antigen. Although similar with respect to populated states in solution, the O-antigen in LPS bilayers has more extended chains as a result of spatial limitations due to close packing. Calcium ions are highly abundant in the phosphate-containing core region mediating LPS LPS association that is crucial for maintaining bilayer integrity, and the negatively charged O-antigen promotes a high concentration of counterbalancing potassium ions. The ensemble of structures present for the PS in solution is captured by the NMR experiments, and the similarities between the O-antigen on its own and as a constituent of the full LPS in a bilayer environment make it possible to realistically describe the LPS conformation and dynamics from the MD simulations.

  • 2. Boutet, Julien
    et al.
    Blasco, Pilar
    Centro de Investigaciones Biológicas, CSIC, Spain.
    Guerreiro, Catherine
    Thouron, Francoise
    Dartevelle, Sylvie
    Nato, Farida
    Javier Canada, F.
    Arda, Ana
    Phalipon, Armelle
    Jimenez-Barbero, Jesus
    Mulard, Laurence A.
    Detailed Investigation of the Immunodominant Role of O-Antigen Stoichiometric O-Acetylation as Revealed by Chemical Synthesis, Immunochemistry, Solution Conformation and STD-NMR Spectroscopy for Shigella flexneri 3a2016In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 22, no 31, p. 10892-10911Article in journal (Refereed)
    Abstract [en]

    Shigella flexneri 3a causes bacillary dysentery. Its O-antigen has the {2)-[alpha-d-Glcp-(1 -> 3)]-alpha-L-Rhap-(1 -> 2)-alpha-L-Rhap-( 1 -> 3)-[Ac -> 2]-alpha-L-Rhap-(1 ->)-[Ac -> 6](approximate to 40%)-beta-D-GlcpNAc-(1 ->} ([(E)AB(Ac)C(Ac)D]) repeating unit, and the non-Oacetylated equivalent defines S. flexneri X. Propyl hepta-, octa-, and decasaccharides sharing the (E') A'BAcCD(E) A sequence, and their non-O-acetylated analogues were synthesized from a fully protected BAcCD(E) A allyl glycoside. The stepwise introduction of orthogonally protected mono-and disaccharide imidate donors was followed by a two-step deprotection process. Monoclonal antibody binding to twenty-six S. flexneri types 3a and X di-to decasaccharides was studied by an inhibition enzyme-linked immunosorbent assay (ELISA) and STD-NMR spectroscopy. Epitope mapping revealed that the 2(C)-acetate dominated the recognition by monoclonal IgG and IgM antibodies and that the BAcCD segment was essential for binding. The glucosyl side chain contributed to a lesser extent, albeit increasingly with the chain length. Moreover, tr-NOESY analysis also showed interaction but did not reveal any meaningful conformational change upon antibody binding.

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