Fig. 3. Unusual orthosteric pocket of GnRH1R.

a Position comparison of elagolix in GnRH1R with small-molecule ligands in class A GPCRs family. The elagolix is shown as stick with cyan carbons, and the ligands from other GPCRs are shown as gray lines. b Structural superposition of GnRH1R with OX2R (gray cartoon, PDB ID: 4S0V), the ligand SUV (suvorexant) of OX2R is shown as green stick. In GnRH1R, two residues L23 and M24 (shown as cyan sticks with sphere) of the N terminus occupy the enlarged orthosteric pocket. c Key residues (sky blue sticks) within 4 Å of both L23 and M24 in GnRH1R. d Dose-dependent responses of GnRH1R WT and mutants (N102^2.65A, Q174^4.60A, and F178^4.64A) to GnRH agonist determined by IP assays. See Supplementary Table 2 for detailed statistical evaluation. HEK293T were transiently transfected with the wild-type or mutant receptors (without PGS) and IP accumulation was measured after stimulation with GnRH ligands for 2 h. EC₅₀ values are expressed as means ± SEM (n = 3) at three times independent experiment repeats with similar results. e Structural superposition of the elagolix-bound GnRH1R with L76 (L76075)-bound NK1R (PDB ID: 6E59), BMS (BMS-193885)-bound NPY1R (PDB ID: 5ZBH), and Bosentan-bound ET_BR (PDB ID: 5XPR), respectively. Those three ligands (L76, BMS, and Bosentan) shown as green stick bound deeply in their corresponding receptor (shown as gray cartoon) orthosteric site. The toggle switch residue W^6.48 is shown as a stick in all four receptors and both M^3.36 and Y^6.51 are shown in sky blue sticks forming the bottom wall of orthosteric pocket of GnRH1R.