Breaking the Limits in Analyzing Carbohydrate Recognition by NMR Spectroscopy: Resolving Branch-Selective Interaction of a Tetra-Antennary N-Glycan with Lectins

The biological recognition of complex-type N-glycans is part of many key physiological and pathological events. Despite their importance, the structural characterization of these events remains unsolved. The inherent flexibility of N-glycans hampers crystallization and the chemical equivalence of individual branches precludes their NMR characterization. By using a chemoenzymatically synthesized tetra-antennary N-glycan conjugated to a lanthanide binding tag, the NMR signals under paramagnetic conditions discriminated all four N-acetyl lactosamine antennae with unprecedented resolution. The NMR data revealed the conformation of the N-glycan and permitted for the first time the direct identification of individual branches involved in the recognition by two N-acetyllactosamine-binding lectins, Datura stramonium seed lectin (DSL) and Ricinus Communis agglutinin (RCA120).