Molecular determinants of A_2AR–D₂R allosterism: role of the intracellular loop 3 of the D₂R

Abstract

In the CNS, an antagonistic interaction has been shown between adenosine A_2A and dopamine D₂ receptors (A_2ARs and D₂Rs) 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/D₂R 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 D₂R within the A_2AR/D₂R oligomer and the dependence of this receptor–receptor interaction on two regions rich in positive charges on intracellular loop 3 of the D₂R. Interestingly, we observed a negative allosteric effect of the D₂R 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 D₂R, 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/D₂R oligomer in living cells.