title: The allosteric enhancer PD81,723 increases chimaeric A1/A2A adenosine receptor coupling with Gs.
abstract: PD81,723 {(2-amino-4,5-dimethyl-3-thienyl)-[3-(trifluromethyl)-phenyl]methanone} is a selective allosteric enhancer of the G(i)-coupled A1 AR (adenosine receptor) that is without effect on G(s)-coupled A2A ARs. PD81,723 elicits a decrease in the dissociation kinetics of A1 AR agonist radioligands and an increase in functional agonist potency. In the present study, we sought to determine whether enhancer sensitivity is dependent on coupling domains or G-protein specificity of the A1 AR. Using six chimaeric A1/A2A ARs, we show that the allosteric effect of PD81,723 is maintained in a chimaera in which the predominant G-protein-coupling domain of the A1 receptor, the 3ICL (third intracellular loop), is replaced with A2A sequence. These chimaeric receptors are dually coupled with G(s) and G(i), and PD81,723 increases the potency of N6-cyclopentyladenosine to augment cAMP accumulation with or without pretreatment of cells with pertussis toxin. Thus PD81,723 has similar functional effects on chimaeric receptors with A1 transmembrane sequences that couple with G(i) or G(s). This is the first demonstration that an allosteric regulator can function in the context of a switch in G-protein-coupling specificity. There is no enhancement by PD81,723 of G(i)-coupled A2A chimaeric receptors with A1 sequence replacing A2A sequence in the 3ICL. The results suggest that the recognition site for PD81,723 is on the A1 receptor and that the enhancer acts to directly stabilize the receptor to a conformational state capable of coupling with G(i) or G(s).
authors.affiliation: Department of Internal Medicine, Cardiovascular Division, University of Virginia Health Sciences Center, Charlottesville, VA 22908, USA.
authors.forename: Samita
authors.initials: S
authors.lastname: Bhattacharya
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: Youkey
authors.forename: Kobina
authors.initials: K
authors.lastname: Ghartey
authors.forename: Matthew
authors.initials: M
authors.lastname: Leonard
authors.forename: Joel
authors.initials: J
authors.lastname: Linden
authors.forename: Amy L
authors.initials: AL
authors.lastname: Tucker
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000494:Allosteric Regulation / Q000187:drug effects*; D000818:Animals; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D004285:Dogs; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism*; D006801:Humans; D007462:Iodobenzenes / Q000494:pharmacology; D007668:Kidney / Q000166:cytology; D011487:Protein Conformation; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D011869:Radioligand Assay; D043682:Receptor, Adenosine A1 / Q000737:chemistry / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D043705:Receptor, Adenosine A2A / Q000737:chemistry / Q000187:drug effects / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D013876:Thiophenes / Q000494:pharmacology*; D014162:Transfection; D014970:Xanthines / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D007462:Iodobenzenes; D043682:Receptor, Adenosine A1; D043705:Receptor, Adenosine A2A; D011993:Recombinant Fusion Proteins; D013876:Thiophenes; D014970:Xanthines; C056346:BW A1433; C075004:PD 81723; C092271:2-(2-(4-amino-3-iodophenyl)ethylamino)adenosine; C048599:N(6)-cyclopentyladenosine; C044323:3-iodo-N(6)-4-aminobenzyladenosine; D000242:Cyclic AMP; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D019205:GTP-Binding Protein alpha Subunits, Gs; D000241:Adenosine