Identification of two C-terminal amino acids, Ser(355) and Thr(357), required for short-term homologous desensitization of mu-opioid receptors

Biochem Pharmacol. 2002 Jul 15;64(2):257-66. doi: 10.1016/s0006-2952(02)01114-0.


Our recent study suggests that a cluster of Ser/Thr residues (T(354)S(355)S(356)T(357)) at the intracellular carboxyl tail of rat mu-opioid receptor (MOR1) is required for the development of short-term homologous desensitization. To investigate the functional role played by individual serine or threonine residue of this (TSST) cluster in the agonist-induced mu-opioid receptor desensitization, point mutant (T354A), (S355A), (S356A) and (T357A) mu-opioid receptors were prepared and stably expressed in human embryonic kidney 293 cells (HEK 293 cells). Similar to wild-type mu-opioid receptors, mutant (T354A) and (S356A) mu-opioid receptors stably expressed in HEK 293 cells developed homologous desensitization after 30 min pretreatment of DAMGO ([D-Ala(2),N-methyl-Phe(4),Gly-ol(5)]enkephalin), a specific mu-opioid receptor agonist. Substituting Ser(355)or Thr(357) with alanine resulted in a significant attenuation of agonist-induced mu-opioid receptor desensitization. In HEK 293 cells stably expressing double mutant (S355A/T357A) mu-opioid receptors, DAMGO pretreatment failed to significantly affect the efficacy and potency by which DAMGO inhibits forskolin-stimulated adenylyl cyclase activity. Consistent with the general belief that agonist-induced phosphorylation of guanine nucleotide binding protein (G protein)-coupled receptors is involved in homologous desensitization. Treating HEK 293 cells expressing wild-type mu-opioid receptors with 5 microM DAMGO for 30 min induced the receptor phosphorylation. Mutation of Ser(355) and Thr(357) also greatly impaired DAMGO-induced mu-opioid receptor phosphorylation. These results suggest that two C-terminal amino acids, Ser(355) and Thr(357), are required for short-term homologous desensitization and agonist-induced phosphorylation of mu-opioid receptors expressed in HEK 293 cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alanine / genetics
  • Alanine / metabolism
  • Amino Acid Substitution
  • Cells, Cultured
  • Humans
  • Phosphorylation
  • Protein Structure, Tertiary
  • Receptors, Opioid, mu / metabolism*
  • Serine / genetics
  • Serine / metabolism*
  • Threonine / genetics
  • Threonine / metabolism*


  • Receptors, Opioid, mu
  • Threonine
  • Serine
  • Alanine