Regulators of G protein signaling 6 and 7. Purification of complexes with gbeta5 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 gamma 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 beta subunits, and certain biochemical properties of RGS6/beta5 and RGS7/beta5 complexes. After expression in Sf9 cells, complexes of both RGS6 and RGS7 with the Gbeta5 subunit (but not Gbetas 1-4) are found in the cytosol. When purified, these complexes are similar to RGS11/beta5 in that they act as GTPase-activating proteins specifically toward Galpha(o). Unlike conventional G(betagamma) complexes, RGS6/beta5 and RGS7/beta5 do not form heterotrimeric complexes with either Galpha(o)-GDP or Galpha(q)-GDP. Neither RGS6/beta5 nor RGS7/beta5 altered the activity of adenylyl cyclases types I, II, or V, nor were they able to activate either Phospholipase C-beta1 or -beta2. However, the RGS/beta5 complexes inhibited beta(1)gamma(2)-mediated activation of Phospholipase C-beta2. RGS/beta5 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 Galpha(o).