Rgs9

RGS9 (regulator of G-protein signaling 9) is one of four members of the R7 subfamily of RGS proteins. Like other R7 RGS proteins, it functions as a GTPase-activating protein (GAP) for the G_i/o family of heterotrimeric G proteins. The action of RGS9 results in the accelerated termination of signaling mediated by G proteins. Several studies have established key roles of RGS9 in the regulation of the following four physiological processes: light reception, locomotion, reward behavior and nociception. At the molecular level the function of RGS9 is best understood in the phototransduction cascade of mammalian rod and cone photoreceptors. In this pathway RGS9 specifically binds to the complex of activated G-protein transducin (G_αt) with its effector enzyme Phosphodiesterase 6 (PDE6) to stimulate G_αt inactivation. Recent evidence indicates that RGS9 is a rate-limiting enzyme in the cascade of reactions that lead to the termination of the photoresponse. Regulation of signaling in reward and movement circuits in the striatum by RGS9 is believed to be achieved through its specific action on G_i/o proteins coupled to dopamine D2 and μ-opioid receptors.