A monomeric G protein-coupled receptor isolated in a high-density lipoprotein particle efficiently activates its G protein.
G protein-coupled receptors (GPCRs) respond to a diverse array of ligands, mediating cellular responses to hormones and neurotransmitters, as well as the senses of smell and taste. The structures of the GPCR rhodopsin and several G proteins have been determined by x-ray crystallography, yet the organization of the signaling complex between GPCRs and G proteins is poorly understood. The observations that some GPCRs are obligate heterodimers, and that many GPCRs form both homo- and heterodimers, has led to speculation that GPCR dimers may be required for efficient activation of G proteins. However, technical limitations have precluded a definitive analysis of G protein coupling to monomeric GPCRs in a biochemically defined and membrane-bound system. Here we demonstrate that a prototypical GPCR, the beta2-adrenergic receptor (beta2AR), can be incorporated into a reconstituted high-density lipoprotein (rHDL) phospholipid bilayer particle together with the stimulatory heterotrimeric G protein, Gs. Single-molecule fluorescence imaging and FRET analysis demonstrate that a single beta2AR is incorporated per rHDL particle. The monomeric beta2AR efficiently activates Gs and displays GTP-sensitive allosteric ligand-binding properties. These data suggest that a monomeric receptor in a lipid bilayer is the minimal functional unit necessary for signaling, and that the cooperativity of agonist binding is due to G protein association with a receptor monomer and not receptor oligomerization.
Whorton
Matthew R
MR
Department of Pharmacology, University of Michigan Medical School, MI 48109, USA.
Bokoch
Michael P
MP
Rasmussen
Søren G F
SG
Huang
Bo
B
Zare
Richard N
RN
Kobilka
Brian
B
Sunahara
Roger K
RK
D000818:Animals; D002417:Cattle; D031541:Fluorescence Resonance Energy Transfer; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D008075:Lipoproteins, HDL / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D008958:Models, Molecular; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D018343:Receptors, Adrenergic, beta-2 / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism*
D008075:Lipoproteins, HDL; D018343:Receptors, Adrenergic, beta-2; D019204:GTP-Binding Proteins