Letter | Published:

Conformational dynamics of a class C G-protein-coupled receptor

Nature volume 524, pages 497501 (27 August 2015) | Download Citation


G-protein-coupled receptors (GPCRs) constitute the largest family of membrane receptors in eukaryotes. Crystal structures have provided insight into GPCR interactions with ligands and G proteins1,2, but our understanding of the conformational dynamics of activation is incomplete. Metabotropic glutamate receptors (mGluRs) are dimeric class C GPCRs that modulate neuronal excitability, synaptic plasticity, and serve as drug targets for neurological disorders3,4. A ‘clamshell’ ligand-binding domain (LBD), which contains the ligand-binding site, is coupled to the transmembrane domain via a cysteine-rich domain, and LBD closure seems to be the first step in activation5,6. Crystal structures of isolated mGluR LBD dimers led to the suggestion that activation also involves a reorientation of the dimer interface from a ‘relaxed’ to an ‘active’ state7,8, but the relationship between ligand binding, LBD closure and dimer interface rearrangement in activation remains unclear. Here we use single-molecule fluorescence resonance energy transfer to probe the activation mechanism of full-length mammalian group II mGluRs. We show that the LBDs interconvert between three conformations: resting, activated and a short-lived intermediate state. Orthosteric agonists induce transitions between these conformational states, with efficacy determined by occupancy of the active conformation. Unlike mGluR2, mGluR3 displays basal dynamics, which are Ca2+-dependent and lead to basal protein activation. Our results support a general mechanism for the activation of mGluRs in which agonist binding induces closure of the LBDs, followed by dimer interface reorientation. Our experimental strategy should be widely applicable to study conformational dynamics in GPCRs and other membrane proteins.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1.

    et al. Crystal structure of the β2 adrenergic receptor-Gs protein complex. Nature 477, 549–555 (2011)

  2. 2.

    , & Structure-function of the G protein-coupled receptor superfamily. Annu. Rev. Pharmacol. Toxicol. 53, 531–556 (2013)

  3. 3.

    & Pharmacology and functions of metabotropic glutamate receptors. Annu. Rev. Pharmacol. Toxicol. 37, 205–237 (1997)

  4. 4.

    & Metabotropic glutamate receptors: physiology, pharmacology, and disease. Annu. Rev. Pharmacol. Toxicol. 50, 295–322 (2010)

  5. 5.

    et al. Locking the dimeric GABAB G-protein-coupled receptor in its active state. J. Neurosci. 24, 370–377 (2004)

  6. 6.

    & Functional insights from glutamate receptor ion channel structures. Annu. Rev. Physiol. 75, 313–337 (2013)

  7. 7.

    et al. Structural basis of glutamate recognition by a dimeric metabotropic glutamate receptor. Nature 407, 971–977 (2000)

  8. 8.

    , , , & Structural views of the ligand-binding cores of a metabotropic glutamate receptor complexed with an antagonist and both glutamate and Gd3+. Proc. Natl Acad. Sci. USA 99, 2660–2665 (2002)

  9. 9.

    , & A practical guide to single-molecule FRET. Nature Methods 5, 507–516 (2008)

  10. 10.

    et al. Single-molecule dynamics of gating in a neurotransmitter transporter homologue. Nature 465, 188–193 (2010)

  11. 11.

    , , , & Conformational dynamics of single G protein-coupled receptors in solution. J. Phys. Chem. B 115, 13328–13338 (2011)

  12. 12.

    et al. Antiparallel EmrE exports drugs by exchanging between asymmetric structures. Nature 481, 45–50 (2011)

  13. 13.

    et al. A general method for the covalent labeling of fusion proteins with small molecules in vivo. Nature Biotechnol. 21, 86–89 (2003)

  14. 14.

    et al. A new approach to analyze cell surface protein complexes reveals specific heterodimeric metabotropic glutamate receptors. FASEB J. 25, 66–77 (2011)

  15. 15.

    et al. Illuminating the activation mechanisms and allosteric properties of metabotropic glutamate receptors. Proc. Natl Acad. Sci. USA 110, E1416–E1425 (2013)

  16. 16.

    et al. Probing cellular protein complexes using single-molecule pull-down. Nature 473, 484–488 (2011)

  17. 17.

    et al. Closed state of both binding domains of homodimeric mGlu receptors is required for full activity. Nature Struct. Mol. Biol. 11, 706–713 (2004)

  18. 18.

    , , , & Structural basis for partial agonist action at ionotropic glutamate receptors. Nature Neurosci. 6, 803–810 (2003)

  19. 19.

    , , & A novel constitutively active mutation in the second cytoplasmic loop of metabotropic glutamate receptor. J. Neurochem. 91, 484–492 (2004)

  20. 20.

    , & Activation switch in the transmembrane domain of metabotropic glutamate receptor. Mol. Pharmacol. 76, 201–207 (2009)

  21. 21.

    , & Structural basis for a Ca2+-sensing function of the metabotropic glutamate receptors. Science 279, 1722–1725 (1998)

  22. 22.

    , , , & Reassessment of the Ca2+ sensing property of a type I metabotropic glutamate receptor by simultaneous measurement of inositol 1,4,5-trisphosphate and Ca2+ in single cells. J. Biol. Chem. 276, 19286–19293 (2001)

  23. 23.

    , , , & Ligand-induced rearrangement of the dimeric metabotropic glutamate receptor 1alpha. Nature Struct. Mol. Biol. 11, 637–642 (2004)

  24. 24.

    et al. Interdomain movements in metabotropic glutamate receptor activation. Proc. Natl Acad. Sci. USA 108, 15480–15485 (2011)

  25. 25.

    et al. Sequential inter- and intrasubunit rearrangements during activation of dimeric metabotropic glutamate receptor 1. Sci. Signal. 5, ra59 (2012)

  26. 26.

    et al. Major ligand-induced rearrangement of the heptahelical domain interface in a GPCR dimer. Nature Chem. Biol. 11, 134–140 (2015)

  27. 27.

    , & Kinetics and mechanism of G protein-coupled receptor activation. Curr. Opin. Cell Biol. 27, 87–93 (2014)

  28. 28.

    et al. Fine tuning of sub-millisecond conformational dynamics controls metabotropic glutamate receptors agonist efficacy. Nature Commun. 5, 5206 (2014)

  29. 29.

    , , & Structures of the extracellular regions of the group II/III metabotropic glutamate receptors. Proc. Natl Acad. Sci. USA 104, 3759–3764 (2007)

  30. 30.

    Noise reduction in single-molecule fluorescence trajectories of folding proteins. Chem. Phys. 307, 137–145 (2004)

  31. 31.

    , & Analysis of single-molecule FRET trajectories using hidden Markov modeling. Biophys. J. 91, 1941–1951 (2006)

  32. 32.

    et al. SSB functions as a sliding platform that migrates on DNA via reptation. Cell 146, 222–232 (2011)

Download references


We thank Z. Fu and H. Okada for technical assistance, J. P. Pin for generously providing the SNAP- and CLIP-tagged mGluRs and advice on their properties, and J. P. Pin, E. Margeat, P. Rondard, A. Jain, A. Reiner and members of the Isacoff laboratory for discussions. Funding was provided by the National Institutes of Health Nanomedicine Development Center for the Optical Control of Biological Function (2PN2EY018241) and the National Science Foundation (EAGER: IOS-1451027). R.V. is a Merck fellow of the Life Science Research Foundation.

Author information

Author notes

    • Reza Vafabakhsh
    •  & Joshua Levitz

    These authors contributed equally to this work.


  1. Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, USA

    • Reza Vafabakhsh
    • , Joshua Levitz
    •  & Ehud Y. Isacoff
  2. Helen Wills Neuroscience Institute, University of California, Berkeley, California 94720, USA

    • Ehud Y. Isacoff
  3. Physical Bioscience Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

    • Ehud Y. Isacoff


  1. Search for Reza Vafabakhsh in:

  2. Search for Joshua Levitz in:

  3. Search for Ehud Y. Isacoff in:


R.V., J.L. and E.Y.I. designed the research. R.V. set up, performed and analysed single-molecule FRET experiments. J.L. performed and analysed ensemble FRET and electrophysiology experiments and contributed to single-molecule FRET experiments. R.V., J.L. and E.IY. wrote the paper.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Ehud Y. Isacoff.

Extended data

About this article

Publication history






Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.