• Cinnamide Derivatives of d -Mannose as Inhibitors of the Bacterial Virulence Factor LecB from Pseudomonas aeruginosa

      Sommer, Roman; Hauck, Dirk; Varrot, Annabelle; Wagner, Stefanie; Audfray, Aymeric; Prestel, Andreas; Möller, Heiko M.; Imberty, Anne; Titz, Alexander; Helmholtz Institute for Pharmaceutical Research Saarland (HIPS);Saarland University, Building A4.1, 66123 Saarbruecken, Germany.; et al. (2015-12)
    • Covalent Lectin Inhibition and Application in Bacterial Biofilm Imaging.

      Wagner, Stefanie; Hauck, Dirk; Hoffmann, Michael; Sommer, Roman; Joachim, Ines; Müller, Rolf; Imberty, Anne; Varrot, Annabelle; Titz, Alexander; HIPS, Helmholtz-Institut für pharmazeutische Forchung Saarland, Universitätscampus E8.1, 66123 Saarbrücken, Germany. (2017-09-28)
      Biofilm formation by pathogenic bacteria is a hallmark of chronic infections. In many cases, lectins play key roles in establishing biofilms. The pathogen Pseudomonas aeruginosa often exhibiting various drug resistances employs its lectins LecA and LecB as virulence factors and biofilm building blocks. Therefore, inhibition of the function of these proteins is thought to have potential in developing "pathoblockers" preventing biofilm formation and virulence. A covalent lectin inhibitor specific to a carbohydrate binding site is described for the first time. Its application in the LecA-specific in vitro imaging of biofilms formed by P. aeruginosa is also reported.
    • Development of a competitive binding assay for the Burkholderia cenocepacia lectin BC2L-A and structure activity relationship of natural and synthetic inhibitors

      Beshr, Ghamdan; Sommer, Roman; Hauck, Dirk; Siebert, David Chan Bodin; Hofmann, Anna; Imberty, Anne; Titz, Alexander (2016)
    • Induction of rare conformation of oligosaccharide by binding to calcium-dependent bacterial lectin: X-ray crystallography and modelling study.

      Lepsik, Martin; Sommer, Roman; Kuhaudomlarp, Sakonwan; Lelimousin, Mickaël; Paci, Emanuele; Varrot, Annabelle; Titz, Alexander; Imberty, Anne; HIPS, Helmholtz-Institut für Pharmazeutische Forschung Saarland, Universitätscampus E8.1 66123 Saarbrücken, Germany. (Elsevier, 2019-09-01)
      Pathogenic micro-organisms utilize protein receptors (lectins) in adhesion to host tissues, a process that in some cases relies on the interaction between lectins and human glycoconjugates. Oligosaccharide epitopes are recognized through their three-dimensional structure and their flexibility is a key issue in specificity. In this paper, we analysed by X-ray crystallography the structures of the LecB lectin from two strains of Pseudomonas aeruginosa in complex with Lewis x oligosaccharide present on cell surfaces of human tissues. An unusual conformation of the glycan was observed in all binding sites with a non-canonical syn orientation of the N-acetyl group of N-acetyl-glucosamine. A PDB-wide search revealed that such an orientation occurs only in 4% of protein/carbohydrate complexes. Theoretical chemistry calculations showed that the observed conformation is unstable in solution but stabilised by the lectin. A reliable description of LecB/Lewis x complex by force field-based methods had proven especially challenging due to the special feature of the binding site, two closely apposed Ca2+ ions which induce strong charge delocalisation. By comparing various force-field parametrisations, we propose a general strategy which will be useful in near future for designing carbohydrate-based ligands (glycodrugs) against other calcium-dependent protein receptors.
    • O-Alkylated heavy atom carbohydrate probes for protein X-ray crystallography: Studies towards the synthesis of methyl 2-O-methyl-L-selenofucopyranoside.

      Sommer, Roman; Hauck, Dirk; Varrot, Annabelle; Imberty, Anne; Künzler, Markus; Titz, Alexander; Helmholtz-Institute for Pharmaceutical Research Saarland (HIPS),Saarland Universitätscampus E8.1, 66123 Saarbrücken, Germany. (2016)
      Selenoglycosides are used as reactive glycosyl donors in the syntheses of oligosaccharides. In addition, such heavy atom analogs of natural glycosides are useful tools for structure determination of their lectin receptors using X-ray crystallography. Some lectins, e.g., members of the tectonin family, only bind to carbohydrate epitopes with O-alkylated ring hydroxy groups. In this context, we report the first synthesis of an O-methylated selenoglycoside, specifically methyl 2-O-methyl-L-selenofucopyranoside, a ligand of the lectin tectonin-2 from the mushroom Laccaria bicolor. The synthetic route required a strategic revision and further optimization due to the intrinsic lability of alkyl selenoglycosides, in particular for the labile fucose. Here, we describe a successful synthetic access to methyl 2-O-methyl-L-selenofucopyranoside in 9 linear steps and 26% overall yield starting from allyl L-fucopyranoside.
    • Virtual Screening Against Carbohydrate-Binding Proteins: Evaluation and Application to Bacterial Burkholderia ambifaria Lectin.

      Dingjan, Tamir; Gillon, Émilie; Imberty, Anne; Pérez, Serge; Titz, Alexander; Ramsland, Paul A; Yuriev, Elizabeth; HIPS, Helmholtz-Institut für Pharmazeutische Forschung Saarland, Universitätscampus E8.1 66123 Saarbrücken, Germany. (American Chemical Society, 2018-09-24)
      Bacterial adhesion to human epithelia via lectins constitutes a therapeutic opportunity to prevent infection. Specifically, BambL (the lectin from Burkholderia ambifaria) is implicated in cystic fibrosis, where lectin-mediated bacterial adhesion to fucosylated lung epithelia is suspected to play an important role. We employed structure-based virtual screening to identify inhibitors of BambL-saccharide interaction with potential therapeutic value. To enable such discovery, a virtual screening protocol was iteratively developed via 194 retrospective screening protocols against 4 bacterial lectins (BambL, BC2L-A, FimH, and LecA) with known ligands. Specific attention was given to the rigorous evaluation of retrospective screening, including calculation of analytical errors for enrichment metrics. The developed virtual screening workflow used crystallographic constraints, pharmacophore filters, and a final manual selection step. The protocol was applied to BambL, predicting 15 active compounds from virtual libraries of approximately 7 million compounds. Experimental validation using fluorescence polarization confirmed micromolar inhibitory activity for two compounds, which were further characterized by isothermal titration calorimetry and surface plasmon resonance. Subsequent testing against LecB from Pseudomonas aeruginosa demonstrated binding specificity of one of the hit compounds. This report demonstrates the utility of virtual screening protocols, integrating ligand-based pharmacophore filtering and structure-based constraints, in the search for bacterial lectin inhibitors.
    • The virulence factor LecB varies in clinical isolates: consequences for ligand binding and drug discovery

      Sommer, Roman; Wagner, Stefanie; Varrot, Annabelle; Nycholat, Corwin M.; Khaledi, Ariane; Häussler, Susanne; Paulson, James C.; Imberty, Anne; Titz, Alexander (2016)