STD NMR experiments detect magnetization that is transferred from a receptor protein to a bound ligand. Only bound ligands show STD effects. The experiment may be combined with virtually any other NMR experiment, and therefore is well suitable to tackle even very complex problems. In particular, in combination with multidimensional NMR a full characterization of a bound ligand out of a mixture is straightforward. STD NMR is extremely robust and gives maximal effects at protein to ligand ratios greater than ca. 1:100. It follows that less than 1 nmol of protein is necessary for screening. With the availability of so called cryo probes it will be possible to work with hundred pmol amounts of protein. The dissociation constant should be in the range between nM and mM. Therefore, STD NMR covers at least two orders of magnitudes more for dissociation constants than trNOE experiments. From competitive STD experiments dissociation constants may be derived.
Schematic display of the STD NMR effect. Saturation of the protein leads to a direct saturation of those parts of ligand(s) in direct contact to the protein. By exchange between bound and free state the saturation is transported to solution and detected by subtracting a spectrum with saturation from a normal spectrum.
STD NMR gives precise information about the binding epitope of the ligand. This is very important information for the design of a potent drug. The optimal drug is of optimal size and optimal shape. The size is deduced from STD NMR, and the shape is delivered by trNOE experiments.