G protein coupled receptor signaling complexes in live cells.

Classical models of receptor (GPCR) and G protein (Gαβγ) signaling based on biochemical studies have proposed that receptor stimulation results in G protein activation (Gα-GTP) and dissociation of the heterotrimer (Gα-GTP + Gβγ) to regulate downstream signaling events. Unclear is whether or not there exists freely diffusible, activated Gα-GTP on cellular membranes capable of catalytic signal amplification. Recent studies in live cells indicate that GPCRs serve as platforms for the assembly of macromolecular signaling complexes that include G proteins to support a highly efficient and spatially restricted signaling event, with no requirement for full Gα-GTP and Gβγ dissociation and lateral diffusion within the plasma membrane.