Fig. 3: Asymmetric dimerization and activation of mGlu2–mGlu3 and mGlu2–mGlu4.

a, b Comparison of the TMDs in the G protein-free, agonist-bound structures of the heterodimers and mGlu2 homodimer (PDB ID: 7EPB). mGlu2–mGlu3 and mGlu2 (a); mGlu2–mGlu4 and mGlu2 (b). The structures are aligned at the mGlu2 subunit of the heterodimer, and shown in an extracellular view. The red arrows indicate the movement of each helix in the mGlu3 subunit (a) or mGlu4 subunit (b) of the heterodimer relative to its counterpart in the homodimer structure. c, d Comparison of the TMDs in the G protein-free and -bound structures of the heterodimers. mGlu2–mGlu3 (c); mGlu2–mGlu4 (d). The structures are aligned at the G protein-free subunits, and shown in both extracellular and intracellular views. The red arrows indicate the movement of each helix in the G_i-bound mGlu2 subunit relative to its counterpart in the G protein-free structure. e–h Glutamate-induced G_i activation of the heterodimers measured by the BRET assay. mGlu2–mGlu3 and mutants (e, g); mGlu2–mGlu4 and mutants (f, h). The superscript ‘X’ indicates that the G protein coupling of the subunit was blocked by introducing a mutation in ICL3 (mGlu2, F756S; mGlu3, F765S; mGlu4, F781S). The BRET data are means ± SEM from at least four independent experiments performed in duplicate. Supplementary information, Table S2 provides detailed independent experiment numbers (n), statistical evaluation, and protein expression levels. i, j Comparison of the conformations of the residue W^6.50 in the two subunits in the G_i-bound heterodimer structures. mGlu2–mGlu3 (i); mGlu2–mGlu4 (j). The residues at positions 5.47 and 6.50 in both subunits are shown as sticks. The PAM JNJ-40411813 bound to the mGlu2 subunit, which stabilizes the active conformation of the residue W773^6.50, is shown as green sticks. The hydrogen bond between the residues D744^5.47 and W782^6.50 in the mGlu3 subunit is indicated by a red dashed line (i). k Comparison of the interactions between the residue 3.59 and the basic residues in helix V and ICL3 of mGlu2 and mGlu3. Due to lack of densities for the residue D671^3.59 in the mGlu2–mGlu3 structures and previously determined mGlu3 homodimer structures, we generated a model of the mGlu3 TMD by SWISS-MODEL server using the mGlu2 TMD structure in the G_i1–mGlu2–mGlu3 complex as a template. The mGlu3 TMD model and mGlu2 TMD structure (PDB ID: 7EPE) are shown in cartoon representation. l Comparison of the interaction between the mGlu residue 3.60 and the Gα_i residue N347 in mGlu2 and mGlu4. The G_i-bound subunits and Gα_i subunits in the G_i-bound structures of mGlu2 and mGlu4 homodimers are shown in cartoon representation.