Constitutive activation of the opioid receptor-like (ORL1) receptor by mutation of Asn133 to tryptophan in the third transmembrane region

J Neurochem. 2002 Dec;83(6):1461-70. doi: 10.1046/j.1471-4159.2002.01231.x.


We have introduced a series of point mutations into the human opioid receptor-like (ORL1) receptor and characterized them for their ability to constitutively activate G protein-coupled receptor signalling pathways. Among the 12 mutants generated, mutation at Asn133 (N133W) gave increased basal signalling through three separate pathways. N133W increased the basal activity of G14- and G16-dependent pathways by two- to three-fold. The constitutive activity of the mutant was confirmed by the finding that the enhanced activity is dependent on the level of receptor expression. In HEK-293 cells stably expressing N133W, signalling through Gi/o-dependent pathways was also observed. Radioligand binding studies revealed that the affinity for nociceptin of the wild-type ORL1 receptor and the N133W mutant do not differ significantly, suggesting that the ligand binding and signalling functions of constitutively active mutants of G protein-coupled receptors are not necessarily intrinsically linked. In conclusion, our results demonstrate that a mutation in the third transmembrane domain is able to increase the basal signalling activity of the human ORL1 receptor.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Substitution
  • Animals
  • Binding, Competitive / physiology
  • COS Cells
  • Cell Line
  • Cyclic AMP / antagonists & inhibitors
  • Cyclic AMP / biosynthesis
  • GTP-Binding Proteins / metabolism
  • Humans
  • Inositol Phosphates / biosynthesis
  • Kidney / cytology
  • Kidney / metabolism
  • Ligands
  • Mutagenesis, Site-Directed
  • Opioid Peptides / metabolism
  • Radioligand Assay
  • Receptors, Opioid / genetics*
  • Receptors, Opioid / metabolism*
  • Signal Transduction / physiology
  • Structure-Activity Relationship
  • Transfection


  • Inositol Phosphates
  • Ligands
  • Opioid Peptides
  • Receptors, Opioid
  • nociceptin
  • nociceptin receptor
  • Cyclic AMP
  • GTP-Binding Proteins