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 and G protein signaling. RGS7 and its binding partners G alpha and G beta 5 are enriched in brain, but biochemical mechanisms governing RGS7/G alpha/G beta 5 interactions and membrane association are poorly defined. We report that RGS7 exists as one cytosolic and three biochemically distinct membrane-bound fractions (salt-extractable, detergent-extractable, and detergent-insensitive) in brain. To define factors that determine RGS7 membrane attachment, we examined the biochemical properties of recombinant RGS7 and G beta 5 synthesized in Spodoptera frugiperda insect cells. We have found that membrane-bound but not cytosolic RGS7 is covalently modified by the fatty acid palmitate. G beta 5 is not palmitoylated. Both unmodified (cytosolic) and palmitoylated (membrane-derived) forms of RGS7, when complexed with G beta 5, are equally effective stimulators of G alpha(o) GTPase activity, suggesting that palmitoylation does not prevent RGS7/G alpha(o) interactions. The isolated 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 alpha(i1) GTPase activities in vitro. In contrast, the RGS7/G beta 5 complex selectively interacts with G alpha(o) only, suggesting that features outside the RGS domain and/or G beta 5 association dictate RGS7-G alpha interactions. These findings define previously unrecognized biochemical properties of RGS7, including the first demonstration that RGS7 is palmitoylated.