Fig. 1: Cryo-EM structures of the human TRHR–G_q complex bound with the endogenous peptide TRH or the orally administered peptide analogue TAL.

a The chemical structures of TRH and TAL. b IP-one accumulation assay of TRHR activation by TRH or TAL. Data are expressed as means ± SEM of three independent experiments conducted in triplicate. c, d Cartoon structural representations of TRH–TRHR–G_q (c) and TAL–TRHR–G_q (d) complexes. The ligand model is shown with a surrounding density map. e The ligand-binding pocket of TRH is magnified, and the black lines represent electrostatic and hydrogen bond interactions. f Ca²⁺ mobilization assay of wild-type and mutant TRHR activation by TRH. Data are expressed as means ± SEM of three independent experiments conducted in triplicate. g The ligand-binding pocket of TAL is magnified, and the black lines represent electrostatic and hydrogen bond interactions. h Ca²⁺ mobilization assays of wild-type and mutant TRHRs with TAL. Data are expressed as means ± SEM of three independent experiments conducted in triplicate. i Space-filling models and cross-sectional views of TRH-bound TRHR and TAL-bound TRHR. j Structural comparison of TRH-bound TRHR and TAL-bound TRHR. The rotamer toggle switch and NPxxY motifs are magnified. k Network of interactions between TAL-bound TRHR (blue) and the Gα5 helix of Gα_q (salmon). l Comparison of the Gα5 helix of the TAL–TRHR–G_q complex and that of the isoprenaline–β₂AR–G_s complex with the receptors aligned. m The TRHR-ICL2–Gα_q interface of TAL-bound TRHR (blue) and the Gα5 helix of Gα_q (salmon).