Heterotrimeric G-proteins

Heterotrimeric G-proteins are made up of three subunits: alpha, beta and gamma. In its resting state, the three subunits are associated together, and GDP is bound to the alpha subunit. The alpha subunit has GTP-hydrolysis activity.

On activation of the receptor, the alpha unit releases GDP and binds GTP, and dissociates from the other subunits. The beta and gamma subunits form a dimer.