RGS6, RGS7, RGS9, and RGS11 Stimulate GTPase Activity of Gi Family G-proteins with Differential Selectivity and Maximal Activity

TLDR

RGS proteins are GTPase‑activating proteins that modulate the amplitude and kinetics of receptor‑mediated heterotrimeric G‑protein signaling. The study aimed to determine the Gα‑subunit selectivity of purified Sf9‑derived R7 RGS proteins (RGS6, 7, 9, and 11). The authors purified Sf9‑derived R7 proteins and examined their Gβ5‑mediated dimeric interaction with Gα subunits. Gβ5/R7 dimers selectively stimulated GTPase activity of Gαi subunits, with RGS9 and RGS11 showing higher potency and efficacy than RGS6/7, RGS11 exhibiting the greatest maximal activity, and RGS7/9 inhibiting RGS11‑mediated Gαo activity, indicating that R7 RGS proteins are Gαi‑selective GAPs with distinct functional profiles.

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 alpha-subunit selectivity of purified Sf9 cell-derived R7 proteins, a subfamily of RGS proteins (RGS6, -7, -9, and -11) containing a Ggamma-like (GGL) domain that mediates dimeric interaction with Gbeta(5). Gbeta(5)/R7 dimers stimulated steady state GTPase activity of Galpha-subunits of the G(i) family, but not of Galpha(q) or Galpha(11), when added to proteoliposomes containing M2 or M1 muscarinic receptor-coupled G-protein heterotrimers. Concentration effect curves of the Gbeta(5)/R7 proteins revealed differences in potencies and efficacies toward Galpha-subunits of the G(i) family. Although all four Gbeta(5)/R7 proteins exhibited similar potencies toward Galpha(o), Gbeta(5)/RGS9 and Gbeta(5)/RGS11 were more potent GAPs of Galpha(i1), Galpha(i2), and Galpha(i3) than were Gbeta(5)/RGS6 and Gbeta(5)/RGS7. The maximal GAP activity exhibited by Gbeta(5)/RGS11 was 2- to 4-fold higher than that of Gbeta(5)/RGS7 and Gbeta(5)/RGS9, with Gbeta(5)/RGS6 exhibiting an intermediate maximal GAP activity. Moreover, the less efficacious Gbeta(5)/RGS7 and Gbeta(5)/RGS9 inhibited Gbeta(5)/RGS11-stimulated GTPase activity of Galpha(o). Therefore, R7 family RGS proteins are G(i) family-selective GAPs with potentially important differences in activities.