Improving ligand affinity through covalent strategies: the case of BC2L-C bacterial lectin

The opportunistic Gram-negative pathogen Burkholderia cenocepacia is a globally spread multidrugresistant bacterium that causes severe lung infections in immunocompromised or cystic fibrosis patients. 1 This bacterium employs lectins as virulence factors to target host tissues through recognition of and adhesion to the glycoconjugates on the host cells’ surface. Among these lectins, the superlectin BC2L-C has been proposed as a major player in the adhesion process and in the formation of bacterial biofilm. 2 In particular, its N-terminal fucose-binding domain (BC2L-C-Nt) represents an interesting target for the design of new antimicrobials that may prevent lectin-mediated bacterial adhesion to the host cells. Recently, we reported the development of a first generation of synthetic ligands targeting BC2L-C-Nt, based on fragment- and structure-based design studies. 3,4Despite the promising results shown by these ligands, the affinity for the N-terminal domain of the target lectin remains in the sub-millimolar range.4,5 With the aim of improving the binding affinity, a new generation of ligands was designed to covalently target specific nucleophilic amino acid residues (Cys72 and Lys108) located near the fucose binding region of BC2L-C-Nt. The new glycomimetics, which contain a L-fucose scaffold connected through a linker to a spacer bearing an electrophilic warhead, were screened in silico through non-covalent and covalent docking protocols, and the most interesting ones were synthetized and subjected to biophysical studies displaying promising results. In particular, the new ligands showed up to a 100-fold affinity gain over the parent monosaccharide resulting in the first synthetic BC2L-C-Nt ligands that reach the micromolar affinity of the fucosylated histoblood oligosaccharides.