mu Opioid receptor: role for the amino terminus as a determinant of ligand binding affinity

Brain Res Mol Brain Res. 2000 Mar 10;76(1):64-72. doi: 10.1016/s0169-328x(99)00332-0.

Abstract

The importance of the amino-terminal domain of the mu opioid receptor (MOR) as a component of the high affinity ligand-binding pocket was evaluated. A deletion mutant lacking 64 amino acids from the amino-terminus of MOR (DeltaN64) was constructed and expressed in HEK 293 cells. The affinities of bremazocine and cyclazocine were similar for the truncated and full-length MORs. Affinities of the mu receptor antagonist, naloxone, and the mu receptor agonist, morphine, were decreased 3.5-fold and 6-fold, respectively, for the truncated receptor relative to the wild-type MOR. Similarly, the affinities of the opioid peptide agonists, DAMGO (Tyr-D-Ala-Gly-MePhe-Gly-ol), beta-endorphin, and DADL (Tyr-D-Ala-Gly-Phe-D-Leu), for the DeltaN64 receptor were decreased from 3- to 8-fold as a result of the deletion. In contrast, the affinities of the alkaloid agonists, methadone and fentanyl, and the peptide agonists, endomorphin 1 and endomorphin 2, for the truncated receptor relative to MOR were reduced dramatically by 20- to 60-fold. MOR is glycosylated when expressed in HEK 293 cells; however, analysis of N-glycosidase F-treated membranes indicated that N-glycan chains within the amino-terminal domain of MOR do not contribute significantly to ligand affinities. These results indicate that amino acid residues within the amino-terminal domain of MOR play a crucial role in the composition of the binding pocket for a select group of agonists.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Alkaloids / metabolism
  • Amino Acid Sequence
  • Amino Acids / genetics
  • Cell Line
  • Humans
  • Hydrolysis
  • Ligands
  • Molecular Sequence Data
  • Peptides / metabolism
  • Polysaccharides / metabolism
  • Radioligand Assay
  • Receptors, Opioid, mu / agonists
  • Receptors, Opioid, mu / genetics
  • Receptors, Opioid, mu / metabolism*
  • Sequence Deletion
  • Structure-Activity Relationship
  • Transfection

Substances

  • Alkaloids
  • Amino Acids
  • Ligands
  • Peptides
  • Polysaccharides
  • Receptors, Opioid, mu