Mutations remote from the human gonadotropin-releasing hormone (GnRH) receptor-binding sites specifically increase binding affinity for GnRH II but not GnRH I: Evidence for ligand-selective, receptor-active conformations

Zhi Liang Lu*, Ryan Gallagher, Robin Sellar, Marla Coetsee, Robert P. Millar

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

60 Citations (Scopus)

Abstract

The human gonadotropin-releasing hormone (GnRH) receptor is evolutionarily configured for high affinity binding of GnRH I ([Tyr5,Leu 7,Arg8GnRH) but at lower affinity for GnRH II ([His 5,Trp7,Tyr8]GnRH). GnRH I is more potent in the activation of the Gq/11 protein in the gonadotrope; however, GnRH II is more potent in the stimulation of apoptosis and antiproliferative effects through activating Gi protein-mediated signaling, implying that GnRH I and II selectively stabilize different receptor-active conformations that preferentially couple to different signaling pathways. Receptor activation involves ligand induction or conformational selection, but the molecular basis of the communication between ligand-binding sites and receptor allosteric sites remains unclear. We have sought conformational coupling between receptor-ligand intermolecular interactions and intramolecular interaction networks in the human GnRH receptor by mutating remote residues that induce differential ligand binding affinity shifts for GnRH I and II. We have demonstrated that certain Ala mutations in the intracellular segments of transmembrane domains 3 (Met 132), 5 (Met227), 6 (Phe272 and Phe 276), and 7 (Ile322 and Tyr323) of the human GnRH receptor allosterically increased ligand binding affinity for GnRH II but had little effect on GnRH I binding affinity. We examined the role of the three amino acids that differ in these two ligands, and we found that Tyr8 in GnRH II plays a dominant role for the increased affinity of the receptor mutants for GnRH II. We propose that creation of a high affinity binding site for GnRH II accompanies receptor conformational changes, i.e. "induced fit" or "conformational selection," mainly determined by the intermolecular interactions between Tyr8 and the receptor contact residues, which can be facilitated by disruption of particular sets of receptor-stabilizing intramolecular interactions. The findings suggest that GnRH I and II binding may selectively stabilize different receptor-active conformations and therefore different ligand-induced selective signaling described previously for these ligands.

Original languageEnglish
Pages (from-to)29796-29803
Number of pages8
JournalJournal of Biological Chemistry
Volume280
Issue number33
DOIs
Publication statusPublished - 19 Aug 2005
Externally publishedYes

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