Transferred Cross-Correlated Relaxation: Application to Drug/Target Complexes

The NMR spectra of biomolecules without and especially with isotopic labeling provide a wealth of information about interatomic distances and angular geometries that can be used as conformational restraints in structure determination. In this review we will focus on the application of cross-correlated relaxation rates to obtain structural information on a small-molecule/protein complex that has pharmaceutical implications. Cross-correlated relaxation complements information derived from NOEs. The chosen complex: epothilone/tubulin could not be subjected to X-ray crystallography. Electron microscopy can only be performed on tubulin sheets induced with Zn ions, which show an assembly of the tubulin dimers that is not found under physiological conditions. A structure of epothilone when bound to tubulin has been determined by electron crystallography. However, the resolution is too low to deduce the conformation of epothilone in a unique way. Thus, NMR constitutes a unique tool for the investigation of this drug/protein complex to obtain a highresolution structure of the drug molecule in the bound state.