title: The role of ligands on the equilibria between functional states of a G protein-coupled receptor.
abstract: G protein-coupled receptors exhibit a wide variety of signaling behaviors in response to different ligands. When a small label was incorporated on the cytosolic interface of transmembrane helix 6 (Cys-265), (19)F NMR spectra of the β2 adrenergic receptor (β2AR) reconstituted in maltose/neopentyl glycol detergent micelles revealed two distinct inactive states, an activation intermediate state en route to activation, and, in the presence of a G protein mimic, a predominant active state. Analysis of the spectra as a function of temperature revealed that for all ligands, the activation intermediate is entropically favored and enthalpically disfavored. β2AR enthalpy changes toward activation are notably lower than those observed with rhodopsin, a likely consequence of basal activity and the fact that the ionic lock and other interactions stabilizing the inactive state of β2AR are weaker. Positive entropy changes toward activation likely reflect greater mobility (configurational entropy) in the cytoplasmic domain, as confirmed through an order parameter analysis. Ligands greatly influence the overall changes in enthalpy and entropy of the system and the corresponding changes in population and amplitude of motion of given states, suggesting a complex landscape of states and substates.
authors.affiliation: Department of Chemistry, University of Toronto, UTM, 3359 Mississauga Road North, Mississauga, Ontario, Canada L5L 1C6.
authors.forename: Tae Hun
authors.initials: TH
authors.lastname: Kim
authors.forename: Ka Young
authors.initials: KY
authors.lastname: Chung
authors.forename: Aashish
authors.initials: A
authors.lastname: Manglik
authors.forename: Alexandar L
authors.initials: AL
authors.lastname: Hansen
authors.forename: Ron O
authors.initials: RO
authors.lastname: Dror
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Mildorf
authors.forename: David E
authors.initials: DE
authors.lastname: Shaw
authors.forename: Brian K
authors.initials: BK
authors.lastname: Kobilka
authors.forename: R Scott
authors.initials: RS
authors.lastname: Prosser
mesh_terms: D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D019906:Nuclear Magnetic Resonance, Biomolecular; D043562:Receptors, G-Protein-Coupled / Q000737:chemistry*; D012243:Rhodopsin / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D008024:Ligands; D043562:Receptors, G-Protein-Coupled; D012243:Rhodopsin