Glycans and Chirality: Stereoselectivity at the Core of DC‐SIGN's Recognition. A Novel View of the Optimum Minimal Ligand Epitope

Glycans exhibit an unparalleled density of stereochemical information, encoded at the monosaccharide level through multiple stereogenic centers, anomeric configurations, ring tautomerism, and conformational variability. Indeed, chiral recognition is fundamental to the interaction between glycans and proteins. Despite the theoretical risk posed by mirror-image molecules, the stereochemical diversity of the "glycan code" enables similar chiral motifs to arise from both D- and L-sugars. Herein, we present an in-depth investigation of the stereochemical features governing lectin-glycan recognition, using the well-characterized human C-type lectin Dendritic cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN) as a model. By combining experimental (STD-NMR) and computational approaches, we identified a minimal optimal binding epitope recognized by DC-SIGN. Key binding requirements include the correct chirality of the Ca²⁺-coordinating oxygens, an adjacent equatorial hydroxyl group for hydrogen bonding with Glu354, and hydrophobic contacts with Val351. Known ligands L-fucose and D-mannose fulfill these criteria. Our results further demonstrate that DC-SIGN also binds α/β-L-galactose, α/β-D-rhamnose, and myo-inositol. Among these, α/β-D-rhamnose exhibits higher affinity than α-OMe-D-mannose, while α/β-L-galactose binds more strongly than D-rhamnose and myo-inositol, although with lower affinity than α-OMe-L-fucose. STD-NMR experiments confirmed that all these ligands share the same core binding epitope.