Allosterism in the adenosine A and cannabinoid CB 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 A receptor and CB 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 AR-CBR heteromer.

KEY RESULTS

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

CONCLUSIONS AND IMPLICATIONS

It is proposed that the AR-CBR heteromer contains distinct dimerization interfaces that govern its functional properties. The molecular interface between protomers of the AR-CBR heteromer interconverted from TM 6 for apo or agonist-bound AR, blocking CBR activation, to mainly the TM 1/7 interface for antagonist-bound AR, 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.