• 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.
    • A rapid synthesis of low-nanomolar divalent LecA inhibitors in four linear steps from d-galactose pentaacetate.

      Zahorska, Eva; Kuhaudomlarp, Sakonwan; Minervini, Saverio; Yousaf, Sultaan; Lepsik, Martin; Kinsinger, Thorsten; Hirsch, Anna K H; Imberty, Anne; Titz, Alexander; HIPS, Helmholtz-Institut für Pharmazeutische Forschung Saarland, Universitätscampus E8.1 66123 Saarbrücken, Germany. (Royal Sciety of Chemistry, 2020-07-06)
      Chronic infections with Pseudomonas aeruginosa are associated with the formation of bacterial biofilms. The tetrameric P. aeruginosa lectin LecA is a virulence factor and an anti-biofilm drug target. Increasing the overall binding affinity by multivalent presentation of binding epitopes can enhance the weak carbohydrate-ligand interactions. Low-nanomolar divalent LecA ligands/inhibitors with up to 260-fold valency-normalized potency boost and excellent selectivity over human galectin-1 were synthesized from d-galactose pentaacetate and benzaldehyde-based linkers in four linear steps.