The Alpha2 adrenergic receptor (AR) inhibits the ubiquitous regulatory enzyme adenylate cyclase via an interaction with a guanine nucleotide binding protein, Ni. This or similar quanine nucleotide binding proteins (N-proteins) may also have other functions such as regulation of phospholipase C or membrane potassium channels. The interaction of the Alpha2 AR with N-proteins has not been well characterized. The experiments will study the factors that control coupling of the Alpha2 AR with N-proteins by use of three approaches. First, selective inactivation of receptors with high and low affinity for agonists will be done to identify receptor heterogeneity that controls the interaction with N-proteins. The effect of such selective modification on inhibition of adenylate cyclase and stimulation of GTPase will also be studied. Second, reconstitution of Alpha2 AR and N-proteins will permit variation in both the identity (Ni vs No) and concentration of the components. Agonist binding will be compared to theoretical predictions for a ternary complex model of receptor N-protein interactions and differences between Alpha2 AR coupling with Ni and No will be evaluated. Finally, studies of solubilized Alpha2 AR using reconstitution, affinity labeling and purification will characterize the structural substrate of Alpha2 AR heterogeneity. A better understanding of Alpha2 AR mechanisms may yield new approaches to the study of pathophysiology and treatment of disorders such as hypertension, Alzheimer's disease and depression.
