Investigation of the Molecular Details of the Interactions of Selenoglycosides and Human Galectin-3

Human galectin-3 (Gal-3) is involved in a variety of biological processes and is implicated in wide range of diseases. As a result, targeting Gal-3 for clinical applications has become an intense area of research. As a step towards the development of novel Gal-3 inhibitors, we describe a study of the binding of two Se-containing Gal-3 inhibitors, specifically that of di(β-D-galactopyranosyl)selenide (SeDG), in which two galactose rings are linked by one Se atom and a di(β-D-galactopyranosyl)diselenide (DSeDG) analogue with a diseleno bond between the two sugar units. The binding affinities of these derivatives to Gal-3 were determined by N-H HSQC NMR spectroscopy and fluorescence anisotropy titrations in solution, indicating a slight decrease in the strength of interaction for SeDG compared to thiodigalactoside (TDG), a well-known inhibitor of Gal-3, while DSeDG displayed a much weaker interaction strength. NMR and FA measurements showed that both seleno derivatives bind to the canonical S face site of Gal-3 and stack against the conserved W181 residue also confirmed by X-ray crystallography, revealing canonical properties of the interaction. The interaction with DSeDG revealed two distinct binding modes in the crystal structure which are in fast exchange on the NMR time scale in solution, explaining a weaker interaction with Gal-3 than SeDG. Using molecular dynamics simulations, we have found that energetic contributions to the binding enthalpies mainly differ in the electrostatic interactions and in polar solvation terms and are responsible for weaker binding of DSeDG compared to SeDG. Selenium-containing carbohydrate inhibitors of Gal-3 showing canonical binding modes offer the potential of becoming novel hydrolytically stable scaffolds for a new class of Gal-3 inhibitors.