RGS Proteins and Signaling by Heterotrimeric G Proteins
A ubiquitously employed mechanism for signal transduction involves ligand binding to a cell surface receptor coupled to a heterotrimeric guanine nucleotide-binding protein (G protein). Receptor activation stimulates nucleotide exchange and dissociation of the G protein, releasing the Gα subunit in its GTP-bound state from the Gβγ complex. The released subunits can stimulate a variety of target (effector) enzymes (1), thereby eliciting biochemical responses and changes in cellular physiology. Hundreds of G protein-coupled receptors have been identified (2, 3).