Skip Header

You are using a version of browser that may not display all the features of this website. Please consider upgrading your browser.

Mu-type opioid receptor



Cavia porcellus (Guinea pig)
Reviewed-Annotation score: Annotation score: 5 out of 5-Protein inferred from homologyi


Receptor for endogenous opioids such as beta-endorphin and endomorphin. Receptor for natural and synthetic opioids including morphine, heroin, DAMGO, fentanyl, etorphine, buprenorphin and methadone (PubMed:8799185). Agonist binding to the receptor induces coupling to an inactive GDP-bound heterotrimeric G-protein complex and subsequent exchange of GDP for GTP in the G-protein alpha subunit leading to dissociation of the G-protein complex with the free GTP-bound G-protein alpha and the G-protein beta-gamma dimer activating downstream cellular effectors. The agonist- and cell type-specific activity is predominantly coupled to pertussis toxin-sensitive G(i) and G(o) G alpha proteins, GNAI1, GNAI2, GNAI3 and GNAO1, and to a lesser extend to pertussis toxin-insensitive G alpha proteins GNAZ and GNA15. They mediate an array of downstream cellular responses, including inhibition of adenylate cyclase activity and both N-type and L-type calcium channels, activation of inward rectifying potassium channels, mitogen-activated protein kinase (MAPK), phospholipase C (PLC), phosphoinositide/protein kinase (PKC), phosphoinositide 3-kinase (PI3K) and regulation of NF-kappa-B. Also couples to adenylate cyclase stimulatory G alpha proteins. The selective temporal coupling to G-proteins and subsequent signaling can be regulated by RGSZ proteins, such as RGS9, RGS17 and RGS4. Phosphorylation by members of the GPRK subfamily of Ser/Thr protein kinases and association with beta-arrestins is involved in short-term receptor desensitization. Beta-arrestins associate with the GPRK-phosphorylated receptor and uncouple it from the G-protein thus terminating signal transduction. The phosphorylated receptor is internalized through endocytosis via clathrin-coated pits which involves beta-arrestins. The activation of the ERK pathway occurs either in a G-protein-dependent or a beta-arrestin-dependent manner and is regulated by agonist-specific receptor phosphorylation. Acts as a class A G-protein coupled receptor (GPCR) which dissociates from beta-arrestin at or near the plasma membrane and undergoes rapid recycling. Receptor down-regulation pathways are varying with the agonist and occur dependent or independent of G-protein coupling. Endogenous ligands induce rapid desensitization, endocytosis and recycling. Heterooligomerization with other GPCRs can modulate agonist binding, signaling and trafficking properties. Involved in neurogenesis (By similarity).By similarity1 Publication

GO - Molecular functioni

GO - Biological processi


Molecular functionG-protein coupled receptor, Receptor, Transducer

Names & Taxonomyi

Protein namesi
Recommended name:
Mu-type opioid receptor
Short name:
Short name:
Gene namesi
OrganismiCavia porcellus (Guinea pig)
Taxonomic identifieri10141 [NCBI]
Taxonomic lineageiEukaryotaMetazoaChordataCraniataVertebrataEuteleostomiMammaliaEutheriaEuarchontogliresGliresRodentiaHystricomorphaCaviidaeCavia
  • UP000005447 Componenti: Unassembled WGS sequence

Subcellular locationi


Feature keyPosition(s)DescriptionActionsGraphical viewLength
Topological domaini‹1 – 9CytoplasmicBy similarity›9
Transmembranei10 – 34Helical; Name=2By similarityAdd BLAST25
Topological domaini35 – 45ExtracellularBy similarityAdd BLAST11
Transmembranei46 – 68Helical; Name=3By similarityAdd BLAST23
Topological domaini69 – 88CytoplasmicBy similarityAdd BLAST20
Transmembranei89 – ›98Helical; Name=4By similarity›10

GO - Cellular componenti

  • axon Source: UniProtKB
  • dendrite Source: UniProtKB
  • endosome Source: UniProtKB
  • integral component of membrane Source: UniProtKB-KW
  • perikaryon Source: UniProtKB-SubCell
  • plasma membrane Source: UniProtKB

Keywords - Cellular componenti

Cell membrane, Cell projection, Endosome, Membrane

Pathology & Biotechi

Chemistry databases


PTM / Processingi

Molecule processing

Feature keyPosition(s)DescriptionActionsGraphical viewLength
ChainiPRO_0000069971‹1 – ›98Mu-type opioid receptorAdd BLAST›98

Amino acid modifications

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Modified residuei71PhosphotyrosineBy similarity1

Post-translational modificationi

Phosphorylated. Differentially phosphorylated in basal and agonist-induced conditions. Agonist-mediated phosphorylation modulates receptor internalization. Phosphorylated by GRK2 in a agonist-dependent manner. Phosphorylated on tyrosine residues; the phosphorylation is involved in agonist-induced G-protein-independent receptor down-regulation (By similarity).By similarity
Phosphorylated. Differentially phosphorylated in basal and agonist-induced conditions. Agonist-mediated phosphorylation modulates receptor internalization. Phosphorylated by GRK2 in a agonist-dependent manner. Phosphorylated on tyrosine residues; the phosphorylation is involved in agonist-induced G-protein-independent receptor down-regulation.By similarity
Ubiquitinated. A basal ubiquitination seems not to be related to degradation. Ubiquitination is increased upon formation of OPRM1:OPRD1 oligomers leading to proteasomal degradation; the ubiquitination is diminished by RTP4.By similarity

Keywords - PTMi

Lipoprotein, Palmitate, Phosphoprotein, Ubl conjugation


Subunit structurei

Forms homooligomers and heterooligomers with other GPCRs, such as OPRD1, OPRK1, OPRL1, NPFFR2, ADRA2A, SSTR2, CNR1 and CCR5 (probably in dimeric forms). Interacts with heterotrimeric G proteins; interaction with a heterotrimeric complex containing GNAI1, GNB1 and GNG2 stabilizes the active conformation of the receptor and increases its affinity for endomorphin-2, the synthetic opioid peptide DAMGO and for morphinan agonists (By similarity). Interacts with PPL; the interaction disrupts agonist-mediated G-protein activation. Interacts (via C-terminus) with DNAJB4 (via C-terminus). Interacts with calmodulin; the interaction inhibits the constitutive activity of OPRM1; it abolishes basal and attenuates agonist-stimulated G-protein coupling. Interacts with FLNA, PLD2, RANBP9 and WLS and GPM6A (By similarity). Interacts with RTP4 (By similarity). Interacts with SYP and GNAS (By similarity). Interacts with RGS9, RGS17, RGS20, RGS4, PPP1R9B and HINT1.By similarity

GO - Molecular functioni

Protein-protein interaction databases


Chemistry databases



3D structure databases


Family & Domainsi

Sequence similaritiesi

Belongs to the G-protein coupled receptor 1 family.PROSITE-ProRule annotation

Keywords - Domaini

Transmembrane, Transmembrane helix

Phylogenomic databases

eggNOGiKOG3656. Eukaryota.

Family and domain databases

InterProiView protein in InterPro
IPR000276. GPCR_Rhodpsn.
IPR017452. GPCR_Rhodpsn_7TM.
IPR001418. Opioid_rcpt.
PfamiView protein in Pfam
PF00001. 7tm_1. 1 hit.
PROSITEiView protein in PROSITE
PS00237. G_PROTEIN_RECEP_F1_1. 1 hit.
PS50262. G_PROTEIN_RECEP_F1_2. 1 hit.


Sequence statusi: Fragment.

P97266-1 [UniParc]FASTAAdd to basket

« Hide

        10         20         30         40         50
60 70 80 90
Mass (Da):11,161
Last modified:May 1, 1997 - v1

Experimental Info

Feature keyPosition(s)DescriptionActionsGraphical viewLength
Non-terminal residuei11
Non-terminal residuei981

Sequence databases

Select the link destinations:
Links Updated
U67928 Genomic DNA. Translation: AAB39617.1.

Similar proteinsi

Links to similar proteins from the UniProt Reference Clusters (UniRef) at 100%, 90% and 50% sequence identity:
100%UniRef100 combines identical sequences and sub-fragments with 11 or more residues from any organism into one UniRef entry.
90%UniRef90 is built by clustering UniRef100 sequences that have at least 90% sequence identity to, and 80% overlap with, the longest sequence (a.k.a seed sequence).
50%UniRef50 is built by clustering UniRef90 seed sequences that have at least 50% sequence identity to, and 80% overlap with, the longest sequence in the cluster.

Entry informationi

Entry nameiOPRM_CAVPO
AccessioniPrimary (citable) accession number: P97266
Entry historyiIntegrated into UniProtKB/Swiss-Prot: July 15, 1998
Last sequence update: May 1, 1997
Last modified: May 10, 2017
This is version 101 of the entry and version 1 of the sequence. See complete history.
Entry statusiReviewed (UniProtKB/Swiss-Prot)
Annotation programChordata Protein Annotation Program


Keywords - Technical termi

Complete proteome, Reference proteome


  1. 7-transmembrane G-linked receptors
    List of 7-transmembrane G-linked receptor entries
  2. SIMILARITY comments
    Index of protein domains and families