What protein complex is associated with inactive G-protein-coupled receptors?

G proteins are indeed the protein complex associated with inactive G-protein-coupled receptors (GPCRs). GPCRs are a vast family of cell surface receptors that play a critical role in various physiological processes by transmitting signals from outside the cell to the inside. When a ligand binds to an inactive GPCR, it causes a conformational change in the receptor, allowing it to interact with G proteins.

When GPCRs are in their inactive state, they are not bound to a G protein or to any ligand. The G protein is composed of three subunits: alpha, beta, and gamma. In the inactive state, the G protein binds to GDP (guanosine diphosphate). When the appropriate ligand binds to the GPCR, the receptor undergoes a conformational change that promotes the exchange of GDP for GTP (guanosine triphosphate) on the alpha subunit of the G protein. This exchange leads to the activation of the G protein, which then dissociates from the receptor and can interact with other signaling molecules in the cell.

Through this mechanism, GPCRs and G proteins form a fundamental signaling pathway that translates extracellular signals into intracellular responses, making G proteins essential partners for the function of inactive