RGS6, RGS7, RGS9, and RGS11 stimulate GTPase activity of Gi family G-proteins with differential selectivity and maximal activity

Abstract

Regulator of G-protein signaling (RGS) proteins are GTPase activating proteins (GAPs) of heterotrimeric G-proteins that alter the amplitude and kinetics of receptor-promoted signaling. In this study we defined the G-protein α-subunit selectivity of purified Sf9 cell-derived R7 proteins, a subfamily of RGS proteins (RGS6,-7, -9, and -11) containing a Gγ-like (GGL) domain that mediates dimeric interaction with Gβ5. Gβ5/R7 dimers stimulated steady state GTPase activity of Gα-subunits of the Gi family, but not of Gαq or Gα11, when added to proteoliposomes containing M2 or M1 muscarinic receptor-coupled G-protein heterotrimers. Concentration effect curves of the Gβ5/R7 proteins revealed differences in potencies and efficacies toward Ga-subunits of the Gi family. Although all four Gβ5/R7 proteins exhibited similar potencies toward Gα0, Gβ5/RGS9 and Gβ5/RGS11 were more potent GAPs of Gαi1, Gαi2, and Gαi3 than were Gβ5/RGS6 and Gβ5/RGS7. The maximal GAP activity exhibited by Gβ5/RGS11 was 2- to 4-fold higher than that of Gβ5/RGS7 and Gβ5/RGS9, with Gβ5/RGS6 exhibiting an intermediate maximal GAP activity. Moreover, the less efficacious Gβ5/RGS7 and Gβ5/RGS9 inhibited Gβ5/ RGS11-stimulated GTPase activity of Gα0. Therefore, R7 family RGS proteins are Gi family-selective GAPs with potentially important differences in activities.