Extended Data Fig. 13: The mechanism of Gs/Golf coupling with mTAAR9.

a, Detailed representation of the mTAAR9-binding interface with Gs. The interface is composed by ICL2, cytoplasmic ends of TM3, TM5, TM6, helix 8 of mTAAR9 (medium aquamarine) and α4-β6 loop, α5 helix, β2-β3 loop of Gs (pink). b, 3D representation of the detailed interactions between the C-terminal end of the α5 helix in the Gαs and mTAAR9.The Y391^G.H5.23, and L388^G.H5.20 form extensive contacts with the hydrophobic surface created by V134^3.54, I220^5.61, A224^5.65 and Q227^5.68 of mTAAR9. c, 3D representation of the detailed interactions between Y391^G.H5.23, E392^G.H5.24, C-terminal carboxyoxylate ends of the α5 helix of Gαs and R130^3.50, K255^6.32 of mTAAR9. Hydrogen bond distances are shown as red dashed lines. Y391^G.H5.23 engages in π: cation interaction with R130^3.50. The E392^G.H5.24 and C-terminal carboxylate ends of the α5 helix of Gαs formed H-bond or charge-charge interactions with K255^6.32 of mTAAR9. d, Overall structure of binding interface of the ICL2 of mTAAR9 with αN, β2-β3 loop, and α5 helix of Gs. e, 3D representation of the detailed interactions between Y140^ICL2, P137^ICL2, L138^ICL2 of mTAAR9 and H41^G.S1.02, V217^G.S3.01, F376^G.H5.08, C379^G.H5.11, R380^G.H5.11, I383^G.H5.15, Q384^G.H5.16, H387^G.H5.19, Y391^G.H5.23 of Gαs. The P137^ICL2 and L138^ICL2 are located in a hydrophobic crater created by H41^G.S1.02, V217^G.S3.01, C379^G.H5.11, F376^G.H5.08, R380^G.H5.12, I383^G.H5.15 and Q384^G.H5.16 of Gαs. Y140^ICL2 is involved in π:π interaction with H387^G.H5.19 and Y391^G.H5.23. The P137^ICL2 and L138^ICL2 are located in a hydrophobic crater created by β1-β3 strands and α5 helix of Gαs. f, 3D representation of the detailed interactions between the C-terminal α5 helix of Gαs and the initial segment in the H8 of mTAAR9. Hydrogen bond distances are shown as red dashed lines. g, Compared to V287^G.S5.02 in Gαs, I274^G.S5.02 in Gαolf has closer association with I263^G.H3.12, W264^G.H3.13, and F260^G.H3.0. At the initial segment in the H8 of mTAAR9, Y315^8.47 and W317^8.49 constitute one sidewall that accommodates the hook end of the C-terminal α5 helix of Gαs and forms a hydrogen bond with R130^3.50 to stabilize the active structure of mTAAR9. h, 3D structural representation of differences between mTAAR9-Golf interface (Golf in medium purple) and mTAAR9-Gs interface (Gs in pink). The comparison of K343^G.h4s6.12/D341^G.h4s6.10 in Gαolf and R356^G.h4s6.12/D354^G.h4s6.10 in Gαs. Hydrogen bond distances are shown as red dashed lines. The K343^G.h4s6.12 and D341^G.h4s6.10 in Gαolf formed weaker charge-charge interactions and are more separated compared with the structural equivalent R356^G.h4s6.12 and D354^G.h4s6.10 pair in Gαs. i, 3D representation of the detailed interactions between V134^ICL2 and V223^5.64 of mTAAR9 and L375^G.H5.20 and Q371^G.H5.16 of Gαolf and superimposition of these interactions with those between V134^ICL2 and V223^5.64 of mTAAR9 and L388^G.H5.20 and Q371^G.H5.16 of Gαs. The conformational changes in cytoplasmic ends of TMD enabled tighter interaction of V223^5.64 and V134^3.54 in mTAAR9 with Q371^G.H5.16 and L37^5G.H5.20 in Gαolf. mTAAR9 bound to Gs is shown in medium aquamarine, mTAAR9 bound to Golf is shown in hot pink, Gs is shown in pink, Golf is shown in medium purple. j, 3D representation of the detailed interactions between R319^8.51 of mTAAR9 and E379^G.H5.24of Gαolf or E392^G.H5.24 of Gαs. At the C-terminus of the α5 helix of Gαolf, E379^G.H5.24 forms stronger charge-charge interactions with R319^8.51 of mTAAR9 compared with those of Gαs. k, 3D representation of the detailed interactions between P141^ICL2, F144^ICL2 of mTAAR9 and K31^G.hns1.02 of Gαolf compared to those between P141^ICL2, F144^ICL2 of mTAAR9 and R38^G.hns1.02 of Gαs (f). Hydrogen bond distances are shown as red dashed lines. Although ICL2 of mTAAR9 forms similar interaction patterns with both Gαs and Gαolf, substituting R38^G.hns1.02 in Gαs by K31^G.hns1.02 in Gαolf abolished the interaction with P141^ICL2 and main chain F144^ICL2 of mTAAR9.