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, (E) under bar GL-10, (p) under bar leckstrin) and GGL ((G) under bar protein <(gamma)under bar> subunit-(l) under bar ike) 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 beta subunits, and certain biochemical properties of RGS6/beta 5 and RGS7/beta 5 complexes. After expression in Sf9 cells, complexes of both RGS6 and RGS7 with the G beta 5 subunit (but not G beta s 1-4) are found in the cytosol. When purified, these complexes are similar to RGS11/beta 5 in that they act as GTPase-activating proteins specifically toward G alpha(o). Unlike conventional G(beta gamma) complexes, RGS6/beta 5 and RGS7/beta 5 do not form heterotrimeric complexes with either G alpha(o)-GDP or G alpha(q)-GDP. Neither RGS6/beta 5 nor RGS7/beta 5 altered the activity of adenylyl cyclases types I, II, or V, nor were they able to activate either phospholipase C-beta 1 or -beta 2. However, the RGS/beta 5 complexes inhibited beta(1)gamma(2)-mediated activation of phospholipase C-beta 2. RGS/beta 5 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 G alpha(o).