Differential capacities of the RGS1, RGS16 and RGS-GAIP regulators of G protein signaling to enhance α2A-adrenoreceptor agonist-stimulated GTPase activity of Go1α

Abstract

Recombinant RGS1, RGS16 and RGS-GAIP, but not RGS2, were able to substantially further stimulate the maximal GTPase activity of Go1α promoted by agonists at the α2A-adrenoreceptor in a concentration-dependent manner. Kinetic analysis of the regulation of an α2A-adrenoreceptor-Go1α fusion protein by all three RGS proteins revealed that they had similar affinities for the receptor-G protein fusion. However, their maximal effects on GTP hydrolysis varied over threefold with RGS16 > RGS1 > RGS-GAIP. Both RGS1 and RGS16 reduced the potency of the α2A-adrenoreceptor agonist adrenaline by some 10-fold. A lower potency shift was observed for the partial agonist UK14304 and the effect was absent for the weak partial agonist oxymetazoline. Each of these RGS proteins altered the intrinsic activity of both UK14304 and oxymetazoline relative to adrenaline. Such results require the RGS interaction with Go1α to alter the conformation of the α2A-adrenoreceptor and are thus consistent with models invoking direct interactions between RGS proteins and receptors. These studies demonstrate that RGS1, RGS16 and RGS-GAIP show a high degree of selectivity to regulate α2A-adrenoreceptor-activated Go1α rather than Gi1α, Gi2α or Gi3α and different capacities to inactivate this G protein.