Screening protein-small molecule interactions by NMR.

Nuclear magnetic resonance (NMR) is well suited to probing the interactions between ligands and macromolecular receptors. It is a truly label-free technique, requiring only the presence of atoms (usually (1)H or (19)F) which give rise to observable resonances on either the ligand or the receptor. A number of parameters associated with these resonances can be used to distinguish rapidly tumbling compounds from ligands which bind to a macromolecular receptor. As such, NMR reports directly on the molecular components involved in the binding interaction whilst avoiding artifacts arising from the addition of an observable label. NMR is also unique amongst biophysical techniques in giving information on the chemical nature of almost all of the constituents present in the sample, thus allowing ready identification of sample, contaminants, degraded material and buffers. Solution phase NMR is also free of artifacts introduced by the presence of a solid support or matrix, although some interesting NMR techniques have been developed to identify ligand-receptor interactions in both solid and heterogeneous phase systems.NMR can readily report on molecular interactions across a wide range of affinities and timescales. Although NMR is not an inherently sensitive technique, the development of cryogenic probeheads over the past decade has dramatically increased the range of applicability of the technique and reduced the stringent sample requirements that used to be regarded as an "Achilles' heel" of NMR. The last, but by no means the least, NMR has the ability to determine structural information at atomic resolution; this has proved to be particularly useful when applied to those protein-ligand systems which cannot be readily crystallized.