Conformational differences in liganded and unliganded states of Galectin-3

The conformation of the carbohydrate recognition domain of Galectin-3, a lectin known to bind galactose containing oligosaccharides in mammalian systems, has been investigated in the absence of ligand and in the presence of N-acetylactosamine. A new methodology based on the measurement of residual dipolar couplings from NMR spectra has been used to characterize differences in protein structure along the backbone in the presence and absence of ligand, as well as the binding geometry of the ligand itself. The data on the ligand are consistent with the ligand binding geometry found in a crystal structure of the complexed state. However, a significant rearrangement of backbone loops near the binding site appears to occur in the absence of ligand. The implications for ligand specificity and protein functionality are discussed.