NMR-based analysis of protein-ligand interactions

Physiological processes are mainly controlled by intermolecular recognition mechanisms involving protein-protein and protein-ligand (low molecular weight molecules) interactions. One of the most important tools for probing these interactions is high-field solution nuclear magnetic resonance (NMR) through protein-observed and ligand-observed experiments, where the protein receptor or the organic compounds are selectively detected. NMR binding experiments rely on comparison of NMR parameters of the free and bound states of the molecules. Ligand-observed methods are not limited by the protein molecular size and therefore have great applicability for analysing protein-ligand interactions. The use of these NMR techniques has considerably expanded in recent years, both in chemical biology and in drug discovery. We review here three major ligand-observed NMR methods that depend on the nuclear Overhauser effect-transferred nuclear Overhauser effect spectroscopy, saturation transfer difference spectroscopy and water-ligand interactions observed via gradient spectroscopy experiments-with the aim of reporting recent developments and applications for the characterization of protein-ligand complexes, including affinity measurements and structural determination.