Molecular Recognition of Complex-Type Biantennary <i>N</i>‑Glycans by Protein Receptors: a Three-Dimensional View on Epitope Selection by NMR

The current surge in defining glycobiomarkers by applying lectins rekindles interest in definition of the sugar-binding sites of lectins at high resolution. Natural complex-type <i>N</i>-glycans can present more than one potential binding motif, posing the question of the actual mode of interaction when interpreting, for example, lectin array data. By strategically combining <i>N</i>-glycan preparation with saturation-transfer difference NMR and modeling, we illustrate that epitope recognition depends on the structural context of both the sugar and the lectin (here, wheat germ agglutinin and a single hevein domain) and cannot always be predicted from simplified model systems studied in the solid state. We also monitor branch-end substitutions by this strategy and describe a three-dimensional structure that accounts for the accommodation of the α2,6-sialyl­ated terminus of a biantennary <i>N</i>-glycan by viscumin. In addition, we provide a structural explanation for the role of terminal α2,6-sialyl­ation in precluding the interaction of natural <i>N</i>-glycans with lectin from Maackia amurensis. The approach described is thus capable of pinpointing lectin-binding motifs in natural <i>N</i>-glycans and providing detailed structural explanations for lectin selectivity