Saturation transfer difference nuclear magnetic resonance study on the specific binding of ligand to protein

Ligand-based nuclear magnetic resonance (NMR) approaches have shown great promise in the study of ligand-protein interaction. But these approaches suffer from interference from the nonspecific binding. Here a saturation transfer difference (STD) NMR method to map the group epitope and to measure the dissociation constant (K_D) of specific interaction between ligand and protein is presented. The interference from nonspecific binding was corrected by recording STD NMR spectra of ligand-protein solutions with and without inhibitor saturating the mutually specific binding site and subtracting one from the other. The method was examined with l-tryptophan (Trp), naproxen (Nap), and human serum albumin (HSA) as model ligand, inhibitor, and protein, respectively. Results agree well with other reports of Trp-HSA interaction.