Exploring Glycan-Lectin Interactions in Natural-Like Environments: A View Using NMR Experiments Inside Cell and on Cell Surface

Glycan-mediated molecular recognition events are essential for life. NMR is widely used to monitor glycan binding to lectins in solution using isolated glycans and lectins. In this context, we herein explore diverse NMR methodologies, from both the receptor and ligand perspectives, to monitor glycan-lectin interactions under experimental conditions mimicking the native milieu inside cells and on cell surface. For the NMR experiments inside cells, galectin-7 is employed as model, since most galectins are soluble and carry out their functions in the cellular micro-environment. Using Danio Rerio oocytes, the 1H-15N HMQC NMR spectrum of a folded galectin has been observed inside cell for the first time, using a glycomimetic ligand (TDG) to overcoming the natural tendency of galectins to bind to numerous galactose-containing receptors within cells. Alternatively, most lectins, other than galectins, are displayed on the cell surface, providing a multivalent presentation to bind their glycan partners in cis (at the same cell) or in trans (on other cells). In this case, ligand-based STD-NMR experiments have been successfully applied to account for the interactions of natural glycans and glycomimetics with Siglec-10. These methodologies provide the proof-of-concept to open the door to the NMR analysis of the recognition of glycans in native-like settings.