title: Pro7.33(303) of the human GnRH receptor regulates selective binding of mammalian GnRH.
abstract: Mammalian gonadotropin releasing hormone (GnRH) receptors have a conserved acidic residue (Glu7.32(301) or Asp7.32(302)) in extracellular loop (ECL) three that confers selectivity for mammalian GnRH, which has Arg8. Comparison of mammalian and non-mammalian GnRH receptors suggested that the acidic residue is not the only determinant of ligand selectivity in mammalian receptors. The acidic residue is followed by a conserved Pro7.33 in mammalian GnRH receptors, but not non-mammalian receptors. Unique structural constraints imposed by Pro residues suggested that Pro7.33 determines selective binding of Arg8-containing GnRH, by stabilising the conformation of the third extracellular loop of the receptor. Substituting Pro7.33(303) or introducing Pro to position 7.31 decreased affinity for GnRH, but not analogs lacking Arg8. Substituting Pro7.33(303) changed the predicted alpha-helix content of the loop-helix interface. These results show that Pro7.33(303) of the human GnRH receptor is required for selective high affinity binding of mammalian GnRH and supports the hypothesis that Pro7.33(303) stabilises a loop conformation that is necessary for selective ligand binding.
authors.affiliation: UCT-MRC Research Group for Receptor Biology, Institute for Infectious Diseases and Molecular Medicine, Division of Medical Biochemistry, University of Cape Town Faculty of Health Sciences, Observatory, Cape Town, 7925, South Africa.
authors.forename: Bernhard J
authors.initials: BJ
authors.lastname: Fromme
authors.forename: Arieh A
authors.initials: AA
authors.lastname: Katz
authors.forename: Robert P
authors.initials: RP
authors.lastname: Millar
authors.forename: Colleen A
authors.initials: CA
authors.lastname: Flanagan
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D017124:Conserved Sequence; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011392:Proline / Q000737:chemistry*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D011966:Receptors, LHRH / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone; D011392:Proline