Protein–Ligand Screening by NMR

This chapter considers NMR methods that are specifically tailored to qualitatively and quantitatively investigate the interaction of small molecules with protein receptors, and as such find use in protein–ligand screening. The basic phenomenon of the ligand binding equilibrium is first introduced, and then various methods to investigate this are described. The methods focus primarily in ligand-observed techniques, and cover the most common approaches, including direct ligand observation with relaxation editing, saturation transfer difference (STD), water-LOGSY (ligand observation with gradient spectroscopy), and exchange-transferred nuclear Overhauser effects (NOEs). The concept of competition experiments for detecting high-affinity ligands is introduced along with the notion of competitive ligand screening via a reporter or spy molecule. Finally, methods that employ observation of the isotopically labelled protein receptor are also introduced as an alternative to ligand-observed techniques.