Affinity measurement of strong ligands with NMR spectroscopy: Limitations and ways to overcome them

NMR spectroscopy is currently extensively used in binding assays for hit identification, but its use in dissociation constant determination is more limited when compared to other biophysical techniques, in particular for tight binders. Although NMR is quite suitable for measuring the binding strength of weak to medium affinity ligands with dissociation constant K_D > 1 μM, it has some limitations in the determination of the binding strength of tight binders (K_D < 1 μM). A theoretical analysis of the binding affinity determination of strong ligands using different types of NMR experiments is provided and practical guidelines are given for overcoming the limitations and for the proper set-up of the experiments. Some approaches require reagents with unique properties or highly specialized equipment, while others can be applied quite generally. We describe all approaches in detail, but give higher emphasis to the more general methods, like competition experiments, where we include actual experimental data and discuss the practical aspects.