RT Journal Article
SR Electronic
T1 Role of Aspartate7.32(302) of the Human Gonadotropin-Releasing Hormone Receptor in Stabilizing a High-Affinity Ligand Conformation
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 1280
OP 1287
DO 10.1124/mol.60.6.1280
VO 60
IS 6
A1 Bernhard J. Fromme
A1 Arieh A. Katz
A1 Roger W. Roeske
A1 Robert P. Millar
A1 Colleen A. Flanagan
YR 2001
UL http://molpharm.aspetjournals.org/content/60/6/1280.abstract
AB Mammalian gonadotropin-releasing hormone (GnRH) receptors preferentially bind mammalian GnRH, which has Arg in position eight. The Glu7.32(301) residue, which determines selectivity of the mouse GnRH receptor for Arg8-containing GnRH, is Asp7.32(302) in the human GnRH receptor. We have confirmed that Asp7.32(302) confers selectivity of the human GnRH receptor for Arg8 of GnRH and investigated the mechanism of this specificity using site-directed mutagenesis and ligand modification. We find that although Arg8 and Asp7.32(302) are required for high-affinity binding of GnRH, conformationally constrained peptides, with d-amino acid substitutions in position six or with a 6,7 γ-lactam, bind the human GnRH receptor with high affinity, which is independent of the presence of Asp7.32(302) in the receptor or Arg8 in the ligand. The ability of the ligand constraints to compensate for the absence of both Arg8 and Asp7.32(302) indicates that these residues both have roles in stabilizing a high affinity ligand conformation and that their roles are complementary. This suggests that the Arg8 and Asp7.32(302) side chains interact to induce a high affinity conformation of native GnRH. Thus, Asp7.32(302) of the human GnRH receptor determines selectivity for mammalian GnRH by its ability to induce a high affinity conformation of its native ligand. However, this initial interaction seems not to contribute to the final ligand-receptor complex. We propose that Arg8 interacts transiently with Asp7.32(302) to induce a high-affinity ligand conformation of GnRH, which then interacts with a binding pocket that is common for both constrained and unconstrained analogs of GnRH.