Emmanuel Margeat

Centre de Biologie Structurale, CNRS, INSERM, Université de Montpellier, France

Structural dynamics of single metabotropic glutamate receptors

Metabotropic glutamate receptors (mGlu) are dimeric, multidomain neuroreceptors belonging to the class C of G protein-coupled receptors.

These membrane proteins are essential in controlling synaptic transmission, and as such are important drug targets for the treatment of several disorders including pain, Parkinson’s disease, schizophrenia,… Allosteric modulators, that display selectivity among the 8 mGlu subtypes are considered highly promising compounds to target these mGlu related brain diseases.

I will cover in this presentation our recent efforts using single molecule fluorescence to investigate the conformational changes, and allosteric transitions associated with ligand-induced mGluR activation.

For that, we established a robust solubilization strategy that allows to maintain full functional integrity of receptors in solution for several days. We further employed genetic code expansion to incorporate non-canonical amino acids and fluorescently label the receptor at selected positions using click chemistry. Therefore, using single molecule FRET, we monitored ligand-dependent inter- and intra-subunit conformational changes.

We demonstrate that the receptor is only partially stabilized in its active state by the natural full agonist glutamate. The addition of a positive allosteric modulator or of purified, heterotrimeric Gi protein, both binding to the 7 transmembrane domains, are necessary to fully reach the fully active state. Our results also show that different orthosteric ligands exert different degrees of conformational changes and underline the allosteric effect on agonist efficacy and potency, mediated through a long-range interdomain communication.

References

• Cao et al. Nat Commun 12, 5426 (2021)
• Lecat-Guillet et al., BioRxiv doi.org/10.1101/2022.01.07.474531426 (2022)