RT Journal Article
SR Electronic
T1 Thermodynamics and Docking of Agonists to the β<sub>2</sub>-Adrenoceptor Determined Using [<sup>3</sup>H](<em>R</em>,<em>R</em>′)-4-Methoxyfenoterol as the Marker Ligand
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 846
OP 854
DO 10.1124/mol.111.077347
VO 81
IS 6
A1 Lawrence Toll
A1 Karolina Pajak
A1 Anita Plazinska
A1 Krzysztof Jozwiak
A1 Lucita Jimenez
A1 Joseph A. Kozocas
A1 Mary J. Tanga
A1 James E. Bupp
A1 Irving W. Wainer
YR 2012
UL http://molpharm.aspetjournals.org/content/81/6/846.abstract
AB 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 β2-adrenergic receptor, we developed a new agonist radioligand for binding assays. [3H](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 β2-adrenoceptor (AR) population as determined with the antagonist [3H]CGP-12177. The β2-AR agonists tested in this study have considerably higher affinity for the agonist conformation of the receptor, and Ki values determined for fenoterol analogs model much better the cAMP activity of the β2-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 [3H]CGP-12177. Finally, computational modeling identified the molecular interactions involved in agonist binding and allow for the prediction of additional novel β2-AR agonists. The study underlines the possibility of using defined radioligand structure to probe a specific conformation of such shape-shifting system as the β2-adrenoceptor.