Using Bioluminescence Resonance Energy Transfer (BRET) to Characterize Agonist-Induced Arrestin Recruitment to Modified and Unmodified G Protein-Coupled Receptors

G protein-coupled receptors (GPCRs) represent ∼25% of current drug targets. Ligand binding to these receptors activates G proteins and arrestins, which are involved in differential signaling pathways. Because functionally selective or biased ligands activate one of these two pathways, they may be superior medications for certain diseases states. The identification of such ligands requires robust drug screening assays for both G protein and arrestin activity. This unit describes protocols for two bioluminescence resonance energy transfer (BRET)-based assays used to monitor arrestin recruitment to GPCRs. One assay requires modification of GPCRs by fusion to a BRET donor or acceptor moiety, whereas the other can detect arrestin recruitment to unmodified GPCRs.