Regulators of G protein signaling 6 and 7. Purification of complexes with Gβ5 and assessment of their effects on G protein-mediated signaling pathways

Regulators of G protein signaling (RGS) proteins that contain DEP (disheveled, EGL-10, pleckstrin) and GGL (G protein γ subunit-like) domains form a subfamily that includes the mammalian RGS proteins RGS6, RGS7, RGS9, and RGS11. We describe the cloning of RGS6 cDNA, the specificity of interaction of RGS6 and RGS7 with G protein β subunits, and certain biochemical properties of RGS6/β5 and RGS7/β5 complexes. After expression in Sf9 cells, complexes of both RGS6 and RGS7 with the Gβ5 subunit (but not Gβs 1-4) are found in the cytosol. When purified, these complexes are similar to RGS11/β5 in that they act as GTPase-activating proteins specifically toward Gα(o). Unlike conventional G(βγ) complexes, RGS6/β5 and RGS7/β5 do not form heterotrimeric complexes with either Gα(o)-GDP or Gα(q)GDP. Neither RGS6/β5 nor RGS7/β5 altered the activity of adenylyl cyclases types I, II, or V, nor were they able to activate either phospholipase C-β1 or -β2. However, the RGS/β5 complexes inhibited β₁γ₂-mediated activation of phospholipase C-β2. RGS/β5 complexes may contribute to the selectivity of signal transduction initiated by receptors coupled to G(i) and G(o) by binding to phospholipase C and stimulating the GTPase activity of Gα(o).