However, the mechanism by which heterotrimeric G proteins are activated by their upstream G protein–coupled receptors (GPCRs) remains obscure. Recent structural data support the idea that GPCRs ...

They consist of heterotrimers of an α-subunit, a β-subunit and a γ-subunit. Upon ligand binding, G-protein-coupled receptors (GPCRs) catalyse the exchange of GDP to GTP on the α-subunit.