Type 5 G protein beta subunit (Gbeta5) controls the interaction of regulator of G protein signaling 9 (RGS9) with membrane anchors.

The R7 family of regulators of G protein signaling (RGS) proteins, comprising RGS6, RGS7, RGS9, and RGS11, regulate neuronal G protein signaling pathways. All members of the R7 RGS form trimeric complexes with the atypical G protein ß subunit, Gß5, and membrane anchor R7BP or R9AP. Association with Gß5 and membrane anchors has been shown to be critical for maintaining proteolytic stability of the R7 RGS proteins. However, despite its functional importance, the mechanism of how R7 RGS forms complexes with Gß5 and membrane anchors remains poorly understood. Here, we used protein-protein interaction, co-localization, and protein stability assays to show that association of RGS9 with membrane anchors requires Gß5. We further establish that the recruitment of R7BP to the complex requires an intact interface between the N-terminal lobe of RGS9 and protein interaction surface of Gß5. Site-directed mutational analysis reveals that distinct molecular determinants in the interface between Gß5 and N-terminal Dishevelled, EGL-10, Pleckstrin/DEP Helical Extension (DEP/DHEY) domains are differentially involved in R7BP binding and proteolytic stabilization. On the basis of these findings, we conclude that Gß5 contributes to the formation of the binding site to the membrane anchors and thus is playing a central role in the assembly of the proteolytically stable trimeric complex and its correct localization in the cell.

Expression and localization of RGS9-2/G 5/R7BP complex in vivo is set by dynamic control of its constitutive degradation by cellular cysteine proteases.

A member of regulator of G-protein signaling family, RGS9-2, is an essential modulator of signaling through neuronal dopamine and opioid G-protein-coupled receptors. Recent findings indicate that the abundance of RGS9-2 determines sensitivity of signaling in the locomotor and reward systems in the striatum. In this study we report the mechanism that sets the concentration of RGS9-2 in vivo, thus controlling G-protein signaling sensitivity in the region. We found that RGS9-2 possesses specific degradation determinants which target it for constitutive destruction by lysosomal cysteine proteases. Shielding of these determinants by the binding partner R7 binding-protein (R7BP) controls RGS9-2 expression at the posttranslational level. In addition, binding to R7BP in neurons targets RGS9-2 to the specific intracellular compartment, the postsynaptic density. Implementation of this mechanism throughout ontogenetic development ensures expression of RGS9-2/type 5 G-protein beta subunit/R7BP complexes at postsynaptic sites in unison with increased signaling demands at mature synapses.