Abstract
The metabotropic glutamate receptor 6 (mGlu6) is essential for synaptic communication of rod photoreceptors, and mutations in mGlu6 lead to a blinding disorder. However, its structural organization remains unknown. Here, we present the structure of agonist-bound mGlu6, revealing an asymmetric dimer arrangement in the absence of a G protein. This indicates that agonist binding alone can induce the homodimeric receptor asymmetry in metabotropic glutamate receptors and structurally prime mGlu6 for activation by pre-organizing the transmembrane domain dimer interface for G protein binding. The structure also identifies noncanonical interactions between the cysteine-rich domain and extracellular loop 2, forming a unique interface that likely stabilizes the activation state. Mutational analyses of this interface reveal its role in maintaining rapid Gαo activation and surface targeting. The structure also permits mechanistic investigation of congenital stationary night blindness and reveals diverse effects of pathogenic mutations on surface trafficking, Gαo coupling, and activation dynamics, including unexpected gain-of-function. These results provide critical insight into the intermediate asymmetric structure of mGlu6 and offer a molecular framework for understanding the pathogenesis of inherited retinal disorders.
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The cryo-EM density maps and corresponding coordinates generated in this study have been deposited in the Electron Microscopy Data Bank (EMDB) and the Protein Data Bank (PDB) under the following accession codes: EMD-63210 and 9LLZ (L-SOP bound mGlu6, global), EMD-63211 and 9LM0 (L-SOP bound mGlu6, local), EMD-64620 and 9UYO (L-SOP bound mGlu6, class 1), EMD-64622 and 9UYQ (L-SOP bound mGlu6, class 2), and EMD-64621 and 9UYP (L-SOP bound mGlu6, class 3). The source data underlying Figs. 1c, d, 4g–j, and 5b, c, and Supplementary Figs. 4b–g and 7b–g are provided in the Source Data file. Uncropped scans of all gels and blots are provided in the Supplementary Information. Source data are provided with this paper.
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Acknowledgements
We thank Dr. Bumhan Ryu at the Institute for Basic Science (IBS) for his assistance in cryo-EM data collection and Dr. Hyeongseop Jeong at the Korea Basic Science Institute (KBSI) for his assistance in cryo-EM data processing. We also thank Yeji Gil, Dong Kyu Chung, and Youngchae Joe for helpful discussions. Use of the cryo-EM facilities of the NEXUS Consortium was supported by a grant from the National Research Foundation of Korea (RS-2024-00440289). The authors thank the National Center for Inter-University Research Facilities (NCIRF) for assistance with cryo-EM. This work was supported by the Samsung Science and Technology Foundation (SSTF-BA2101-13 to H.H.L.) and NIH grants EY018139 and EY034339 (to K.A.M.).
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S.Y.L., C.-T.C., Y.Y., K.A.M., and H.H.L. conceived and designed the experiments. S.Y.L. solved the cryo-EM structures and performed the structural analyses. C.-T.C. performed biochemical assays. Y.Y. and J.S.J. helped with cryo-EM data collection and analysis. S.Y.L., C.-T.C., Y.Y., J.S.J., K.A.M., and H.H.L. analyzed the data and wrote the manuscript. K.A.M. and H.H.L. directed the work. All the authors have edited the manuscript.
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Lee, S.Y., Chang, CT., Yun, Y. et al. CryoEM structure of mGlu6 captures receptor activation prior to G protein coupling. Nat Commun (2026). https://doi.org/10.1038/s41467-026-70436-w
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DOI: https://doi.org/10.1038/s41467-026-70436-w
