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Nature. 2015 Aug 20;524(7565):375-8. doi: 10.1038/nature14680. Epub 2015 Aug 5.

Propagation of conformational changes during μ-opioid receptor activation.

Author information

1
Institut de Genomique Fonctionnelle, CNRS UMR-5203 INSERM U1191, University of Montpellier, F-34000 Montpellier, France.
2
Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium.
3
Structural Biology Research Center, VIB, Pleinlaan 2, B-1050 Brussels, Belgium.
4
Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305, USA.
5
Centre de Biochimie Structurale, CNRS UMR 5048-INSERM 1054- University of Montpellier, 29 rue de Navacelles, 34090 Montpellier Cedex, France.

Abstract

µ-Opioid receptors (µORs) are G-protein-coupled receptors that are activated by a structurally diverse spectrum of natural and synthetic agonists including endogenous endorphin peptides, morphine and methadone. The recent structures of the μOR in inactive and agonist-induced active states (Huang et al., ref. 2) provide snapshots of the receptor at the beginning and end of a signalling event, but little is known about the dynamic sequence of events that span these two states. Here we use solution-state NMR to examine the process of μOR activation using a purified receptor (mouse sequence) preparation in an amphiphile membrane-like environment. We obtain spectra of the μOR in the absence of ligand, and in the presence of the high-affinity agonist BU72 alone, or with BU72 and a G protein mimetic nanobody. Our results show that conformational changes in transmembrane segments 5 and 6 (TM5 and TM6), which are required for the full engagement of a G protein, are almost completely dependent on the presence of both the agonist and the G protein mimetic nanobody, revealing a weak allosteric coupling between the agonist-binding pocket and the G-protein-coupling interface (TM5 and TM6), similar to that observed for the β2-adrenergic receptor. Unexpectedly, in the presence of agonist alone, we find larger spectral changes involving intracellular loop 1 and helix 8 compared to changes in TM5 and TM6. These results suggest that one or both of these domains may play a role in the initial interaction with the G protein, and that TM5 and TM6 are only engaged later in the process of complex formation. The initial interactions between the G protein and intracellular loop 1 and/or helix 8 may be involved in G-protein coupling specificity, as has been suggested for other family A G-protein-coupled receptors.

PMID:
26245377
PMCID:
PMC4820006
DOI:
10.1038/nature14680
[Indexed for MEDLINE]
Free PMC Article

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