Impact of aromatic residues within transmembrane helix 6 of the human gonadotropin-releasing hormone receptor upon agonist and antagonist binding.
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 Y(283), Y(284), W(289), Y(290), W(291), and F(292) were exchanged to alanine and analyzed comprehensively in functional reporter gene and ligand binding assays. Whereas receptor mutants Y(283)A, Y(284)A, and W(291)A were capable of neither ligand binding nor signal transduction, mutants W(289)A, Y(290)A, and F(292)A were functional: the F(292)A mutant behaved like wild-type receptor, while mutants W(289)A and Y(290)A 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-Trp(6)-GnRH (Triptorelin) binding, representing a superagonistic ligand, is in full accordance to available data. Furthermore, new interactions are proposed: pGlu(1) interacts with N(212) in transmembrane helix 5, Tyr(5) with Y(290), and D-Trp(6) with W(289). The binding behavior of mutants W(289)A and Y(290)A corresponds to the proposed binding model for the antagonist Cetrorelix. In summary, our data as presented indicate that Y(290) plays a key function in agonist but not antagonist binding.
Hövelmann
Sascha
S
Department of Cancer Research, ASTA Medica AG, Weismüllerstrasse 45, D-60314 Frankfurt/Main, Germany.
Hoffmann
Silke H
SH
Kühne
Ronald
R
ter Laak
Ton
T
Reiländer
Helmut
H
Beckers
Thomas
T
D000595:Amino Acid Sequence; D001483:Base Sequence; D017931:DNA Primers; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011966:Receptors, LHRH / Q000737:chemistry / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
D017931:DNA Primers; D008565:Membrane Proteins; D011966:Receptors, LHRH