title: Probing the beta2 adrenoceptor binding site with catechol reveals differences in binding and activation by agonists and partial agonists.
abstract: The beta(2) adrenergic receptor (beta(2)AR) is a prototypical family A G protein-coupled receptor (GPCR) and an excellent model system for studying the mechanism of GPCR activation. The beta(2)AR agonist binding site is well characterized, and there is a wealth of structurally related ligands with functionally diverse properties. In the present study, we use catechol (1,2-benzenediol, a structural component of catecholamine agonists) as a molecular probe to identify mechanistic differences between beta(2)AR activation by catecholamine agonists, such as isoproterenol, and by the structurally related non-catechol partial agonist salbutamol. Using biophysical and pharmacologic approaches, we show that the aromatic ring of salbutamol binds to a different site on the beta(2)AR than the aromatic ring of catecholamines. This difference is important in receptor activation as it has been hypothesized that the aromatic ring of catecholamines plays a role in triggering receptor activation through interactions with a conserved cluster of aromatic residues in the sixth transmembrane segment by a rotamer toggle switch mechanism. Our experiments indicate that the aromatic ring of salbutamol does not activate this mechanism either directly or indirectly. Moreover, the non-catechol ring of partial agonists does not interact optimally with serine residues in the fifth transmembrane helix that have been shown to play an important role in activation by catecholamines. These results demonstrate unexpected differences in binding and activation by structurally similar agonists and partial agonists. Moreover, they provide evidence that activation of a GPCR is a multistep process that can be dissected into its component parts using agonist fragments.
authors.affiliation: Department of Molecular and Cellular Physiology, Stanford University School of Medicine, 157 Beckman Circle, Stanford, CA 94305, USA.
authors.forename: Gayathri
authors.initials: G
authors.lastname: Swaminath
authors.forename: Xavier
authors.initials: X
authors.lastname: Deupi
authors.forename: Tae Weon
authors.initials: TW
authors.lastname: Lee
authors.forename: Wen
authors.initials: W
authors.lastname: Zhu
authors.forename: Foon Sun
authors.initials: FS
authors.lastname: Thian
authors.forename: Tong Sun
authors.initials: TS
authors.lastname: Kobilka
authors.forename: Brian
authors.initials: B
authors.lastname: Kobilka
mesh_terms: D000420:Albuterol / Q000737:chemistry; D000818:Animals; D001665:Binding Sites; D001669:Biochemical Phenomena; D001671:Biochemistry; D002395:Catecholamines / Q000737:chemistry; D002396:Catechols / Q000737:chemistry*; D006801:Humans; D007313:Insecta; D007545:Isoproterenol / Q000737:chemistry; D007700:Kinetics; D008024:Ligands; D008055:Lipids / Q000737:chemistry; D008954:Models, Biological; D008956:Models, Chemical; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D018343:Receptors, Adrenergic, beta-2 / Q000737:chemistry*; D043562:Receptors, G-Protein-Coupled / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013997:Time Factors
chemical_list: D002395:Catecholamines; D002396:Catechols; D008024:Ligands; D008055:Lipids; D018343:Receptors, Adrenergic, beta-2; D043562:Receptors, G-Protein-Coupled; D007545:Isoproterenol; C034221:catechol; D000420:Albuterol