Applications of fluorescence in the characterization of the ligand-binding domain and activation of the cholecystokinin receptor

Fluorescence techniques can be applied to guanine nucleotide-binding protein-coupled receptors to gain insights into the environment and molecular motion of a fluorophore that is either incorporated into a ligand or more directly into a specific site within the receptor. Fluorescence studies can provide insight into the environment of that indicator. By situating the same indicator into an analogous position in both agonist and antagonist ligands, comparisons can provide insights into differences between active and inactive states of the receptor. These types of studies have been performed for the cholecystokinin receptor and show that receptor activation by agonist occupation is associated with a movement of the CCK-like ligand out of a protected environment and into a more accessible hydrophilic milieu.