Conformational Preferences of the O‑Antigen Polysaccharides of Escherichia coli O5ac and O5ab Using NMR Spectroscopy and Molecular Modeling

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

Conformational Preferences of the O‑Antigen Polysaccharides of Escherichia coli O5ac and O5ab Using NMR Spectroscopy and Molecular Modeling

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

Conformational Preferences of the O‑Antigen Polysaccharides of Escherichia coli O5ac and O5ab Using NMR Spectroscopy and Molecular Modeling

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

Interactions between Pectic Compounds and Procyanidins are Influenced by Methylation Degree and Chain Length

The interactions between procyanidins and pectic compounds are of importance in food chemistry. Procyanidins with low (9) and high (30) average degrees of polymerization (DP9 and DP30) were extracted from two cider apple varieties. Commercial apple and citrus pectins, as well as three pectin subfractions (homogalacturonans, partially methylated homogalacturonans with degree of methylation 30 and 70) at 30 mM galacturonic acid equivalent, were titrated with the two procyanidin fractions (at 30 mM (−)-epicatechin equivalent) by isothermal titration calorimetry and UV–vis spectrophotometry. Slightly stronger affinities were recorded between commercial apple or citrus pectins and procyanidins of DP30 (<i>K</i>_a = 1460 and 1225 M^–1 respectively, expressed per monomer units) compared to procyanidins of DP9 (<i>K</i>_a = 1240 and 1085 M^–1, respectively), but stoichiometry and absorbance maxima differed between apple and citrus pectins. It was proposed that methylated homogalacturonans interacted with procyanidins DP30 mainly through hydrophobic interactions. The stronger association was obtained with the longer procyanidin molecules interacting with highly methylated pectins

Engineering of PA-IIL lectin from – Unravelling the role of the specificity loop for sugar preference-3

<p><b>Copyright information:</b></p><p>Taken from "Engineering of PA-IIL lectin from – Unravelling the role of the specificity loop for sugar preference"</p><p>http://www.biomedcentral.com/1472-6807/7/36</p><p>BMC Structural Biology 2007;7():36-36.</p><p>Published online 1 Jun 2007</p><p>PMCID:PMC1903359.</p><p></p>uffer (pH = 7.5) with 30 μM CaCl. A) Data obtained from 29 automatic injections (10 μL) of Me-α-Man each into the S23A-containing cell. B)Plot of the total heat released as a function of ligand/protein molar ratio for the titration shown in panel A. The solid represents the best least-squares fit for the obtained data

Engineering of PA-IIL lectin from – Unravelling the role of the specificity loop for sugar preference-4

<p><b>Copyright information:</b></p><p>Taken from "Engineering of PA-IIL lectin from – Unravelling the role of the specificity loop for sugar preference"</p><p>http://www.biomedcentral.com/1472-6807/7/36</p><p>BMC Structural Biology 2007;7():36-36.</p><p>Published online 1 Jun 2007</p><p>PMCID:PMC1903359.</p><p></p>and PA-IIL wild type (red) by affinity chromatography on Mannose agarose column (HR 10/10). Loading buffer: 20 mM Tris/HCl, 100 mM NaCl, 100 μM CaCl, pH 7.5; Elution buffer: 20 mM Tris/HCl, 100 mM NaCl, 100 μM CaCl, 0.1 M D-mannose, pH 7.5; Sample: cytoplasmic soluble protein fractions

Increasing the Hydrophilicity of Cyclic Ketene Acetals Improves the Hydrolytic Degradation of Vinyl Copolymers and the Interaction of Glycopolymer Nanoparticles with Lectins

Radical ring-opening polymerization (rROP) of cyclic ketene acetals (CKAs) with traditional vinyl monomers allows the synthesis of degradable vinyl copolymers. However, since the most commonly used CKAs are hydrophobic, most degradable vinyl copolymers reported so far degrade very slowly by hydrolysis under physiological conditions (phosphate-buffered saline, pH 7.4, 37 °C), which can be detrimental for biomedical applications. Herein, to design advanced vinyl copolymers by rROP with high CKA content and enhanced degradation profiles, we reported the copolymerization of 2-methylene-1,3,6-trioxocane (MTC) as a CKA with vinyl ether (VE) or maleimide (MI) derivatives. By performing a point-by-point comparison between the MTC/VE and MTC/MI copolymerization systems, and their counterparts based on 2-methylene-1,3-dioxepane (MDO) and 5,6-benzo-2-methylene-1,3-dioxepane (BMDO), we showed negligible impact on the macromolecular characteristics and similar reactivity ratios, suggesting successful substitution of MDO and BMDO by MTC. Interestingly, owing to the hydrophilicity of MTC, the obtained copolymers exhibited a faster hydrolytic degradation under both accelerated and physiological conditions. We then prepared MTC-based glycopolymers, which were formulated into surfactant-free nanoparticles, exhibiting excellent colloidal stability up to 4 months and complete degradation under enzymatic conditions. Importantly, MTC-based glyconanoparticles also showed a similar cytocompatibility toward two healthy cell lines and a much stronger lectin affinity than MDO-based glyconanoparticles

Engineering of PA-IIL lectin from – Unravelling the role of the specificity loop for sugar preference-0

<p><b>Copyright information:</b></p><p>Taken from "Engineering of PA-IIL lectin from – Unravelling the role of the specificity loop for sugar preference"</p><p>http://www.biomedcentral.com/1472-6807/7/36</p><p>BMC Structural Biology 2007;7():36-36.</p><p>Published online 1 Jun 2007</p><p>PMCID:PMC1903359.</p><p></p>ht brown. Interactions responsible for sugar preference are in yellow, newly created hydrogen bonds are in blue. Figure clearly demonstrates different orientation of O6 of methyl mannoside

The Hidden Conformation of Lewis x, a Human Histo-Blood Group Antigen, Is a Determinant for Recognition by Pathogen Lectins

Histo-blood group epitopes are fucosylated branched oligosaccharides with well-defined conformations in solution that are recognized by receptors, such as lectins from pathogens. We report here the results of a series of experimental and computational endeavors revealing the unusual distortion of histo-blood group antigens by bacterial and fungal lectins. The Lewis x trisaccharide adopts a rigid closed conformation in solution, while crystallography and molecular dynamics reveal several higher energy open conformations when bound to the <i>Ralstonia solanacearum</i> lectin, which is in agreement with thermodynamic and kinetic measurements. Extensive molecular dynamics simulations confirm rare transient Le^x openings in solution, frequently assisted by distortion of the central N-acetyl-glucosamine ring. Additional directed molecular dynamic trajectories revealed the role of a conserved tryptophan residue in guiding the fucose into the binding site. Our findings show that conformational adaptation of oligosaccharides is of paramount importance in cell recognition and should be considered when designing anti-infective glyco-compounds

Multivalent Glycomimetics with Affinity and Selectivity toward Fucose-Binding Receptors from Emerging Pathogens

Bacterial and fungal pathogens involved in lung infection in cystic fibrosis patients utilize a particular family of glycan-binding proteins, characterized by the presentation of six fucose-binding sites on a ring-shaped scaffold. These lectins are attractive targets for anti-infectious compounds that could interfere in the recognition of host tissues by pathogens. The design of a cyclopeptide-based hexavalent structure allowed for the presentation of six fucose residues. The synthetic hexavalent compound displays liable geometry resulting in high-avidity binding by lectins from <i>Aspergillus fumigatus</i> and <i>Burkholderia ambifaria</i>. Replacing the fucose residue with a conformationally constrained fucomimetic does not alter the affinity and provides fine specificity with no binding to other fucose-specific lectins