Allosterism in the adenosine A 2A and cannabinoid CB 2 heteromer.

BACKGROUND AND PURPOSE: Allosterism is a regulatory mechanism for GPCRs that can be attained by ligand-binding or protein-protein interactions with another GPCR. We have studied the influence of the dimer interface on the allosteric properties of the A2A receptor and CB2 receptor heteromer.

EXPERIMENTAL APPROACH: We have evaluated cAMP production, phosphorylation of signal-regulated kinases (pERK1/2), label-free dynamic mass redistribution, β-arrestin 2 recruitment and bimolecular fluorescence complementation assays in the absence and presence of synthetic peptides that disrupt the formation of the heteromer. Molecular dynamic simulations provided converging evidence that the heteromeric interface influences the allosteric properties of the A2A R-CB2 R heteromer.

KEY RESULTS: Apo A2A R blocks agonist-induced signalling of CB2 R. The disruptive peptides, with the amino acid sequence of transmembrane (TM) 6 of A2A R or CB2 R, facilitate CB2 R activation, suggesting that A2A R allosterically prevents the outward movement of TM 6 of CB2 R for G protein binding. Significantly, binding of the selective antagonist SCH 58261 to A2A R also facilitated agonist-induced activation of CB2 R.

CONCLUSIONS AND IMPLICATIONS: It is proposed that the A2A R-CB2 R heteromer contains distinct dimerization interfaces that govern its functional properties. The molecular interface between protomers of the A2A R-CB2 R heteromer interconverted from TM 6 for apo or agonist-bound A2A R, blocking CB2 R activation, to mainly the TM 1/7 interface for antagonist-bound A2A R, facilitating the independent opening of intracellular cavities for G protein binding. These novel results shed light on a different type of allosteric mechanism and extend the repertoire of GPCR heteromer signalling.