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The heterotrimeric G protein complex composed of Gα, Gβ, and Gγ subunits serves as one of the key signal transducers in eukaryotes.In animals, heterotrimeric G proteins are activated by G protein-coupled receptors (GPCRs) that perceive various extracellular signals.In the absence of a stimulus, the GDPbound Gα monomer and Gβγ dimer form an inactive heterotrimer in complex with a GPCR.Ligand binding to the GPCR triggers the exchange of GDP with GTP in Gα and subsequent dissociation of Gα from Gβγ, both of which further interact with a subset of effector proteins to activate downstream signaling cascades (Urano and Jones, 2014).