G protein coupled receptors (GPCRs) are a family of proteins involved in cellular signal transduction. In canonical G protein signaling, GPCRs receive extracellular signals in the form of hormones, neurotransmitters, and other ligands. GPCRs then activate heterotrimeric G proteins, which include subunits α (GTP binding), β, and γ. These G proteins then are able to activate different intracellular signal cascades and effector proteins.