title: Thermodynamics and docking of agonists to the β(2)-adrenoceptor determined using [(3)H](R,R')-4-methoxyfenoterol as the marker ligand.
abstract: G protein-coupled receptors (GPCRs) are integral membrane proteins that change conformation after ligand binding so that they can transduce signals from an extracellular ligand to a variety of intracellular components. The detailed interaction of a molecule with a G protein-coupled receptor is a complicated process that is influenced by the receptor conformation, thermodynamics, and ligand conformation and stereoisomeric configuration. To better understand the molecular interactions of fenoterol analogs with the β(2)-adrenergic receptor, we developed a new agonist radioligand for binding assays. [(3)H](R,R')-methoxyfenoterol was used to probe the binding affinity for a series of fenoterol stereoisomers and derivatives. The results suggest that the radioligand binds with high affinity to an agonist conformation of the receptor, which represents approximately 25% of the total β(2)-adrenoceptor (AR) population as determined with the antagonist [(3)H]CGP-12177. The β(2)-AR agonists tested in this study have considerably higher affinity for the agonist conformation of the receptor, and K(i) values determined for fenoterol analogs model much better the cAMP activity of the β(2)-AR elicited by these ligands. The thermodynamics of binding are also different when interacting with an agonist conformation, being purely entropy-driven for each fenoterol isomer, rather than a mixture of entropy and enthalpy when the fenoterol isomers binding was determined using [(3)H]CGP-12177. Finally, computational modeling identified the molecular interactions involved in agonist binding and allow for the prediction of additional novel β(2)-AR agonists. The study underlines the possibility of using defined radioligand structure to probe a specific conformation of such shape-shifting system as the β(2)-adrenoceptor.
authors.affiliation: Torrey Pines Institute for Molecular Studies, 11350 SW Village Parkway, Port St. Lucie, FL 34987, USA. ltoll@tpims.org
authors.forename: Lawrence
authors.initials: L
authors.lastname: Toll
authors.forename: Karolina
authors.initials: K
authors.lastname: Pajak
authors.forename: Anita
authors.initials: A
authors.lastname: Plazinska
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Jozwiak
authors.forename: Lucita
authors.initials: L
authors.lastname: Jimenez
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Kozocas
authors.forename: Mary J
authors.initials: MJ
authors.lastname: Tanga
authors.forename: James E
authors.initials: JE
authors.lastname: Bupp
authors.forename: Irving W
authors.initials: IW
authors.lastname: Wainer
mesh_terms: D000318:Adrenergic beta-Agonists / Q000737:chemistry / Q000494:pharmacology*; D002460:Cell Line; D005280:Fenoterol / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D006801:Humans; D008958:Models, Molecular; D011412:Propanolamines / Q000737:chemistry / Q000494:pharmacology; D011869:Radioligand Assay; D018343:Receptors, Adrenergic, beta-2 / Q000737:chemistry / Q000187:drug effects*; D013816:Thermodynamics
chemical_list: D000318:Adrenergic beta-Agonists; D011412:Propanolamines; D018343:Receptors, Adrenergic, beta-2; C550094:methoxyfenoterol; D005280:Fenoterol; C033394:CGP 12177