Allosterism in the adenosine A<sub>2A</sub> and cannabinoid CB<sub>2</sub> heteromer
Claudia Llinás del Torrent, Iu Raïch, Ángel González, Jaume Lillo, Nil Casajuana-Martín, Rafael Franco, Leonardo Pardo, Gemma Navarro
Abstract
Abstract 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 A 2A receptor and CB 2 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 A 2A R–CB 2 R heteromer. Key Results Apo A 2A R blocks agonist‐induced signalling of CB 2 R. The disruptive peptides, with the amino acid sequence of transmembrane (TM) 6 of A 2A R or CB 2 R, facilitate CB 2 R activation, suggesting that A 2A R allosterically prevents the outward movement of TM 6 of CB 2 R for G protein binding. Significantly, binding of the selective antagonist SCH 58261 to A 2A R also facilitated agonist‐induced activation of CB 2 R. Conclusions and Implications It is proposed that the A 2A R–CB 2 R heteromer contains distinct dimerization interfaces that govern its functional properties. The molecular interface between protomers of the A 2A R–CB 2 R heteromer interconverted from TM 6 for apo or agonist‐bound A 2A R, blocking CB 2 R activation, to mainly the TM 1/7 interface for antagonist‐bound A 2A 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. LINKED ARTICLES This article is part of a themed issue Complexity of GPCR Modulation and Signaling (ERNST). To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v182.14/issuetoc