Functionality of Melatonin Receptors: Recruitment of β-Arrestin at MT1

The main process of downregulation of G protein-coupled receptors is desensitization by which the receptor is extruded from the plasma membrane and directed to the endosomal compartment for recycling. Typically, the first step of this phenomenon consists in the recruitment of the protein β-arrestin induced by the agonist. Melatonin receptors undergo the same process: melatonin leads to the recruitment of β-arrestin and is subsequently sent away from the membrane, leading to a de facto stop of the melatonin receptor-mediated G protein signaling, because the receptors are not at the membrane level to receive the message brought by melatonin. The way one can measure this recruitment is based on the elegant technique of enzyme fragment complementation by which two parts of an enzyme are fused to two partners and reform an active enzyme upon the formation of the complex between these two partners. The basic way to set up this technique is presented here.