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Free keywords:
Protein-coupled receptors; Human gnrh receptor; Ligand interaction; Expression; Sites; Overexpression; Hypogonadism; Activation; Contribute; Mechanisms; Binding; X-ray structure
Abstract:
To investigate the impact of aromatic residues within transmembrane helix 6 (TMH6) of the human gonadotropin-releasing hormone receptor (GnRH-R) on agonist and antagonist binding, residues pY283, Y284, W289, Y290, W291, and F202 were exchanged to alanine and analyzed comprehensively in functional reporter gene and ligand binding assays. Whereas receptor mutants Y283A, Y281A, and W291A were capable of neither ligand binding nor signal transduction, mutants W219A, Y290A, and F292A were functional: the F292A mutant behaved like wild-type receptor, while mutants W289A and Y290A differentiated between agonistic and antagonistic ligands. On the basis of the high-resolution X-ray structure of bovine rhodopsin as well as available data on GnRH-R mutants, models for ligand-receptor interactions are proposed. The model for D-Trp6-GnRH (Triptorelin) binding, representing a superagonistic ligand, is in full accordance to available data. Furthermore, new interactions are proposed: pGlu1 interacts with N212 in transmembrane helix 5, Tyr5 with Y290, and D-Trp6 with W289. The binding behavior of mutants W289A and Y290A corresponds to the proposed binding model for the antagonist Cetrorelix. In summary, our data as presented indicate that Y290 plays a key function in agonist but not antagonist binding.
