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.