Bovine Heart Galectin-1 Selects a Unique (Syn) Conformation of C-Lactose, a Flexible Lactose Analogue

The C-glycoside analogue of lactose harbors a pronounced flexibility in water with three conformers in equilibrium. The bound conformation of C-lactose to bovine heart galectin-1 in solution has been determined by NMR spectroscopy. It is demonstrated that the lectin selects the syn conformation of the structural analogue of natural lactose and not the global minimum, anti conformation. The bound conformer resembles those found in the crystal structures of complexes of galectin-1/ N -acetyllactosamine-containing oligosaccharides and in solution for an avian galectin. Docking of the analogue within the galectin's binding site furnishes explanations, in structural terms, for the exclusive recognition of the syn conformer.