Structural requirements for the activation of the human growth hormone secretagogue receptor by peptide and nonpeptide secretagogues

Mol Endocrinol. 1998 Jan;12(1):137-45. doi: 10.1210/mend.12.1.0051.


Antibodies raised against an intracellular and extracellular domain of the GH secretagogue receptor (GHS-R) confirmed that its topological orientation in the lipid bilayer is as predicted for G protein-coupled receptors with seven transmembrane domains. A strategy for mapping the agonist-binding site of the human GHS-R was conceived based on our understanding of ligand binding in biogenic amine and peptide hormone G protein-coupled receptors. Using site-directed mutagenesis and molecular modeling, we classified GHS peptide and nonpeptide agonist binding in the context of its receptor environment. All peptide and nonpeptide ligand classes shared a common binding domain in transmembrane (TM) region 3 of the GHS-R. This finding was based on TM-3 mutation E124Q, which eliminated the counter-ion to the shared basic N+ group of all GHSs and resulted in a nonfunctional receptor. Restoration of function for the E124Q mutant was achieved by a complementary change in the MK-0677 ligand through modification of its amine side-chain to the corresponding alcohol. Contacts in other TM domains [TM-2 (D99N), TM-5 (M213K, S117A), TM-6 (H280F), and extracellular loop 1 (C116A)] of the receptor revealed specificity for the different peptide, benzolactam, and spiroindolane GHSs. GHS-R agonism, therefore, does not require identical disposition of all agonist classes at the ligand-binding site. Our results support the hypothesis that the ligand-binding pocket in the GHS-R is spatially disposed similarly to the well characterized catechol-binding site in the beta2-adrenergic receptor.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • GTP-Binding Proteins / chemistry*
  • GTP-Binding Proteins / genetics
  • GTP-Binding Proteins / metabolism*
  • GTP-Binding Proteins / physiology
  • Human Growth Hormone / chemistry
  • Human Growth Hormone / genetics
  • Human Growth Hormone / metabolism*
  • Humans
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Peptides / chemistry
  • Peptides / genetics
  • Peptides / metabolism*
  • Peptides / physiology*
  • Rats
  • Receptors, Cell Surface / chemistry*
  • Receptors, Cell Surface / genetics
  • Receptors, Cell Surface / metabolism*
  • Receptors, G-Protein-Coupled*
  • Receptors, Ghrelin
  • Swine


  • Peptides
  • Receptors, Cell Surface
  • Receptors, G-Protein-Coupled
  • Receptors, Ghrelin
  • Human Growth Hormone
  • GTP-Binding Proteins