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Keywords:

  • A2AR;
  • D2R;
  • FRET ;
  • oligomerization;
  • allosterism;
  • fluorescent agonist

Abstract

In the CNS, an antagonistic interaction has been shown between adenosine A2A and dopamine D2 receptors (A2ARs 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 A2AR/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 A2AR/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 A2AR 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 A2AR/D2R oligomer in living cells.