title: Structure and function of an irreversible agonist-β(2) adrenoceptor complex.
abstract: G-protein-coupled receptors (GPCRs) are eukaryotic integral membrane proteins that modulate biological function by initiating cellular signalling in response to chemically diverse agonists. Despite recent progress in the structural biology of GPCRs, the molecular basis for agonist binding and allosteric modulation of these proteins is poorly understood. Structural knowledge of agonist-bound states is essential for deciphering the mechanism of receptor activation, and for structure-guided design and optimization of ligands. However, the crystallization of agonist-bound GPCRs has been hampered by modest affinities and rapid off-rates of available agonists. Using the inactive structure of the human β(2) adrenergic receptor (β(2)AR) as a guide, we designed a β(2)AR agonist that can be covalently tethered to a specific site on the receptor through a disulphide bond. The covalent β(2)AR-agonist complex forms efficiently, and is capable of activating a heterotrimeric G protein. We crystallized a covalent agonist-bound β(2)AR-T4L fusion protein in lipid bilayers through the use of the lipidic mesophase method, and determined its structure at 3.5 Å resolution. A comparison to the inactive structure and an antibody-stabilized active structure (companion paper) shows how binding events at both the extracellular and intracellular surfaces are required to stabilize an active conformation of the receptor. The structures are in agreement with long-timescale (up to 30 μs) molecular dynamics simulations showing that an agonist-bound active conformation spontaneously relaxes to an inactive-like conformation in the absence of a G protein or stabilizing antibody.
authors.affiliation: Department of Molecular and Cellular Physiology, Stanford University School of Medicine, 279 Campus Drive, Stanford, California 94305, USA.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Rosenbaum
authors.forename: Cheng
authors.initials: C
authors.lastname: Zhang
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Lyons
authors.forename: Ralph
authors.initials: R
authors.lastname: Holl
authors.forename: David
authors.initials: D
authors.lastname: Aragao
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Arlow
authors.forename: Søren G F
authors.initials: SG
authors.lastname: Rasmussen
authors.forename: Hee-Jung
authors.initials: HJ
authors.lastname: Choi
authors.forename: Brian T
authors.initials: BT
authors.lastname: Devree
authors.forename: Roger K
authors.initials: RK
authors.lastname: Sunahara
authors.forename: Pil Seok
authors.initials: PS
authors.lastname: Chae
authors.forename: Samuel H
authors.initials: SH
authors.lastname: Gellman
authors.forename: Ron O
authors.initials: RO
authors.lastname: Dror
authors.forename: David E
authors.initials: DE
authors.lastname: Shaw
authors.forename: William I
authors.initials: WI
authors.lastname: Weis
authors.forename: Martin
authors.initials: M
authors.lastname: Caffrey
authors.forename: Peter
authors.initials: P
authors.lastname: Gmeiner
authors.forename: Brian K
authors.initials: BK
authors.lastname: Kobilka
mesh_terms: D058666:Adrenergic beta-2 Receptor Agonists / Q000737:chemistry* / Q000378:metabolism*; D003460:Crystallization; D018360:Crystallography, X-Ray; D004220:Disulfides / Q000737:chemistry / Q000378:metabolism; D054314:Drug Inverse Agonism; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D017265:Procaterol / Q000737:chemistry / Q000378:metabolism; D011412:Propanolamines / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D018343:Receptors, Adrenergic, beta-2 / Q000737:chemistry* / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D014764:Viral Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D058666:Adrenergic beta-2 Receptor Agonists; D004220:Disulfides; D008051:Lipid Bilayers; D011412:Propanolamines; D018343:Receptors, Adrenergic, beta-2; D011993:Recombinant Fusion Proteins; D014764:Viral Proteins; C068293:gene 5 protein, Enterobacteria phage T4; C014382:carazolol; D020962:Heterotrimeric GTP-Binding Proteins; D017265:Procaterol