文摘
To investigate the impact of aromatic residues within transmembrane helix 6 (TMH6) of thehuman gonadotropin-releasing hormone receptor (GnRH-R) on agonist and antagonist binding, residuesY283, Y284, W289, Y290, W291, and F292 were exchanged to alanine and analyzed comprehensively in functionalreporter gene and ligand binding assays. Whereas receptor mutants Y283A, Y284A, and W291A were capableof neither ligand binding nor signal transduction, mutants W289A, Y290A, and F292A were functional: theF292A mutant behaved like wild-type receptor, while mutants W289A and Y290A differentiated betweenagonistic and antagonistic ligands. On the basis of the high-resolution X-ray structure of bovine rhodopsinas well as available data on GnRH-R mutants, models for ligand-receptor interactions are proposed. Themodel for D-Trp6-GnRH (Triptorelin) binding, representing a superagonistic ligand, is in full accordanceto available data. Furthermore, new interactions are proposed: pGlu1 interacts with N212 in transmembranehelix 5, Tyr5 with Y290, and D-Trp6 with W289. The binding behavior of mutants W289A and Y290Acorresponds to the proposed binding model for the antagonist Cetrorelix. In summary, our data as presentedindicate that Y290 plays a key function in agonist but not antagonist binding.