Molecular determinants of A 2AR-D 2R allosterism: Role of the intracellular loop 3 of the D 2R

摘要

In the CNS, an antagonistic interaction has been shown between adenosine A 2A and dopamine D 2 receptors (A 2ARs and D 2Rs) that may be relevant both in normal and pathological conditions (i.e., Parkinson's disease). Thus, the molecular determinants mediating this receptor-receptor interaction have recently been explored, as the fine tuning of this target (namely the A 2AR/D 2R oligomer) could possibly improve the treatment of certain CNS diseases. Here, we used a fluorescence resonance energy transfer-based approach to examine the allosteric modulation of the D 2R within the A 2AR/D 2R oligomer and the dependence of this receptor-receptor interaction on two regions rich in positive charges on intracellular loop 3 of the D 2R. Interestingly, we observed a negative allosteric effect of the D 2R agonist quinpirole on A 2AR ligand binding and activation. However, these allosteric effects were abolished upon mutation of specific arginine residues (217-222 and 267-269) on intracellular loop 3 of the D 2R, thus demonstrating a major role of these positively charged residues in mediating the observed receptor-receptor interaction. Overall, these results provide structural insights to better understand the functioning of the A 2AR/D 2R oligomer in living cells. In the native A 2AR/D 2R oligomer (left panel), a bidirectional negative allosteric receptor-receptor interaction may outline the final adenylyl cyclase signaling efficacy by balancing G αs- and G αi/o-coupling. When the arginine residues located on the third intracellular loop of the D 2R are mutated (D 2Rmut; right panel), the negative allosteric receptor-receptor interaction is lost, and a predominant D 2R-mediated adenylyl cyclase inhibition is observed.