The second extracellular loop of the adenosine A1 receptor mediates activity of allosteric enhancers.
Allosteric enhancers of the adenosine A1 receptor amplify signaling by orthosteric agonists. Allosteric enhancers are appealing drug candidates because their activity requires that the orthosteric site be occupied by an agonist, thereby conferring specificity to stressed or injured tissues that produce adenosine. To explore the mechanism of allosteric enhancer activity, we examined their action on several A1 receptor constructs, including (1) species variants, (2) species chimeras, (3) alanine scanning mutants, and (4) site-specific mutants. These findings were combined with homology modeling of the A1 receptor and in silico screening of an allosteric enhancer library. The binding modes of known docked allosteric enhancers correlated with the known structure-activity relationship, suggesting that these allosteric enhancers bind to a pocket formed by the second extracellular loop, flanked by residues S150 and M162. We propose a model in which this vestibule controls the entry and efflux of agonists from the orthosteric site and agonist binding elicits a conformational change that enables allosteric enhancer binding. This model provides a mechanism for the observations that allosteric enhancers slow the dissociation of orthosteric agonists but not antagonists.
Department of Pharmacology (D.P.K.), Department of Molecular Physiology and Biological Physics (S.A.L., M.P., H.F., M.C., R.F., M.Y.), Cardiovascular Research Center (M.A.M., R.F., M.Y.), Center for Membrane Biology (M.Y.), and Department of Medicine, Division of Cardiovascular Medicine (M.Y.), University of Virginia School of Medicine, Charlottesville, Virginia; the Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, California (F.M.M., R.A.); and the La Jolla Institute for Allergy and Immunology (J.L.), La Jolla, California.
Dylan P
DP
Kennedy
Fiona M
FM
McRobb
Susan A
SA
Leonhardt
Michael
M
Purdy
Heidi
H
Figler
Melissa A
MA
Marshall
Mahendra
M
Chordia
Robert
R
Figler
Joel
J
Linden
Ruben
R
Abagyan
Mark
M
Yeager
D000494:Allosteric Regulation; D000818:Animals; D001665:Binding Sites; D004285:Dogs; D057809:HEK293 Cells; D006801:Humans; D008958:Models, Molecular; D062105:Molecular Docking Simulation; D016297:Mutagenesis, Site-Directed; D043682:Receptor, Adenosine A1 / Q000737:chemistry* / Q000502:physiology*; D013045:Species Specificity; D013329:Structure-Activity Relationship
D043682:Receptor, Adenosine A1