RGS7 is palmitoylated and exists as biochemically distinct forms

(R) under bar egulator of (G) under bar protein (s) under bar ignaling (RGS ) proteins are GTPase-activating proteins that modulate neurotransmitter an d G protein signaling. RGS7 and its binding partners G alpha and G beta 5 a re enriched in brain, but biochemical mechanisms governing RGS7/G alpha/G b eta 5 interactions and membrane association are poorly defined. We report t hat RGS7 exists as one cytosolic and three biochemically distinct membrane- bound fractions (salt-extractable, detergent-extractable, and detergent-ins ensitive) in brain. To define factors that determine RGS7 membrane attachme nt, we examined the biochemical properties of recombinant RGS7 and G beta 5 synthesized in Spodoptera frugiperda insect cells. We have found that memb rane-bound but not cytosolic RGS7 is covalently modified by the fatty acid palmitate. G beta 5 is not palmitoylated. Both unmodified (cytosolic) and p almitoylated (membrane-derived) forms of RGS7, when complexed with G beta 5 , are equally effective stimulators of G alpha(o) GTPase activity, suggesti ng that palmitoylation does not prevent RGS7/G alpha(o) interactions. The i solated core RGS domain of RGS7 selectively binds activated G alpha(i/o) in brain extracts and is an effective stimulator of both G alpha(o) and G alp ha(i1) GTPase activities in vitro. In contrast, the RGS7/G beta 5 complex s electively interacts with G alpha(o) only, suggesting that features outside the RGS domain and/or G beta 5 association dictate RGS7-G alpha interactio ns. These findings define previously unrecognized biochemical properties of RGS7, including the first demonstration that RGS7 is palmitoylated.