Structural Basis of Asymmetric Class C GPCR activation and distinct Gq coupling induced by force stimulation
Mechanosensation is essential for diverse physiological processes. While many G protein-coupled receptors (GPCRs) are known to be mechanosensitive, the underlying mechanism remains largely unknown. Here, we reveal that mechanical force induces Gq activation of mGlu2, a balance modulator residing in kinocilia, but not other 7 mGlu members. Force activates mGlu2 through a conserved N-terminal force transduction motif (FTM) via a unique cis mechanism. We engineered a potent FTM-derived peptide agonist that recapitulates force-induced activation and resolved cryo-EM structures of apo-mGlu2, FTM-mGlu2, LFTM-{Psi}EK-mGlu2 and LFTM-{Psi}EK-mGlu2-Gq. The structures reveal that an atypical FTM binding to a previously uncharacterized pocket induces asymmetric 7TM domain rearrangement, enabling Gq coupling via an ICL1-TM3/6/7 interface, fundamentally distinct from the glutamate-induced Gi coupling mode of mGlu2. Compared with Gi-coupled mGlu2, the 5 helix of Gq rotated by 180{degrees}, penetrating deeper (8 [A]) into a hydrophobic pocket. Disruption of the M7947.32-F7806.57-F7766.53 hydrophobic triad core and a conformational propagation path predominantly comprising TM6-7 residues are identified as key elements mediating force induced mGlu2 activation. Further In vivo rescue experiments support that mGlu2s mechanosensitivity is dependent on FTM and is required for vestibular function. This work establishes a paradigm for class C GPCR mechanotransduction, revealing unprecedented structural mechanisms underlying force-induced Gq coupling and offering a chemical toolset to modulate mechanical signaling of GPCR.