Time resolved FRET strategy with fluorescent ligands to analyze receptor interactions in native tissues: application to GPCR oligomerization.

G protein-coupled receptors (GPCRs) play a key role in the regulation of physiological functions. Deregulation of their activities often results in pathological disorders and therefore these receptors constitute major targets for drug development. The emergence of new concepts such as GPCR oligomerization has modified our understanding of these proteins, and identifying the role of receptor complexes is probably a major challenge for the next decade. Various experimental strategies have been developed to study GPCR oligomers and energy transfer experiments between partners within a complex constitute one of the most convenient approaches. These experimental strategies usually require receptor fusion to tags or fluorescent or luminescent proteins and therefore cannot be easily applied to native tissues. We developed a new experimental approach based on the labeling of receptors with high affinity fluorescent ligands compatible with time-resolved energy transfer measurements. Because of the very high signal-to-noise ratio of the time-resolved fluorescent energy transfer (TR-FRET) signals, this approach constitutes a breakthrough since it allows the direct identification of wild-type GPCR oligomers in native tissues.