Opioid receptor
From Wikipedia, the free encyclopedia
Opioid receptors are a group of G-protein coupled receptors with opioids as ligands. The endogenous opioids are dynorphins, enkephalins, endorphins, endomorphins and nociceptin/orphanin FQ. The opioid receptors are ~40% identical to somatostatin receptors (SSTRs).
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[edit] Types of receptors
There are three major subtypes of opioid receptors:[1]
| Receptor | Subtypes | Location[2] | Function [2] |
|---|---|---|---|
| delta (δ) OP1 (I) |
δ1, δ2 |
|
|
| kappa (κ) OP2 (I) |
κ1, κ2, κ3 | ||
| mu (μ) OP3 (I) |
μ1, μ2, μ3 |
|
μ1:
μ2:
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(I). Name based on order of discovery
Sigma receptors (σ) were once considered to be opioid receptors, but are not usually currently classified as such.
The receptors were named using the first letter of the first ligand that was found to bind to them. Morphine was the first chemical shown to bind to mu receptors. The first letter of the drug morphine is `m', but in biochemistry there is a tendency to use Greek letters, thus turning the 'm' to μ. Similarly a drug known as ketocyclazocine was first shown to attach itself to kappa receptors.[3]
The opioid receptor types are ~70% identical with differences located at N and C termini. The μ receptor (the μ represents morphine) is perhaps the most important. It is thought that the G protein binds to the third intracellular loop of the opioid receptors. Both in mice and humans the genes for the various receptor subtypes are located on different chromosomes.
Separate subtypes have been identified in human tissue. Research has so far failed to identify the genetic evidence of the subtypes, and it is thought that they arise from post-translational modification of cloned receptor types.[4]
An additional opioid receptor has been identified and cloned based on homology with the cDNA. This receptor is known as the nociceptin receptor or ORL 1 receptor.
An IUPHAR (International Union of Pharmacology) subcommittee (2000)[5][6] has recommended that appropriate terminology for the 3 classical (μ, δ, κ) receptors, and the non-classical (nociceptin) receptor, should be MOP, DOP, KOP and NOP respectively.
[edit] References
- ^ Corbett AD, Henderson G, McKnight AT, Paterson SJ (2006). "75 years of opioid research: the exciting but vain quest for the Holy Grail". Br. J. Pharmacol. 147 Suppl 1: S153-62. doi:. PMID 16402099.
- ^ a b Fine, Perry G.; Russell K. Portenoy (2004). "Chapter 2: The Endogenous Opioid System", A Clinical Guide to Opioid Analgesia. McGraw Hill.
- ^ Anil Aggrawal (1995-05-01). Opium: the king of narcotics. BLTC Research. Retrieved on 2008-03-21.
- ^ Lemke, Thomas L.; Williams, David H.; Foye, William O. (2002). "Opioid Analgesics; Fries, DS", Foye's principles of medicinal chemistry. Hagerstwon, MD: Lippincott Williams & Wilkins. ISBN 0-683-30737-1.
- ^ Cox BM, Chavkin C, Christie MJ, Civelli O, Evans C, Hamon MD, et al (2006). "75 years of opioid research: the exciting but vain quest for the Holy Grail". Br. J. Pharmacol. 147 Suppl 1: S153-62. doi:. PMID 16402099.
- ^ Girdlestone, D (October 2000). "Opioid receptors; Cox BM, Chavkin C, Christie MJ, Civelli O, Evans C, Hamon MD, et al", The IUPHAR Compendium of Receptor Characterization and Classification, 2nd Edition, London: IUPHAR Media, pages 321-333.
[edit] See also
[edit] External links
- MeSH Opioid+Receptors
- IUPHAR GPCR Database - Opioid Receptors. International Union of Basic and Clinical Pharmacology (2007-10-15). Retrieved on 2008-03-21.
- Corbett A, McKnight S, Henderson G. Opioid Receptors. BLTC Research. Retrieved on 2008-03-21.
- Lomize A, Lomize M, Pogozheva I. Orientations of Proteins in Membranes (OPM) database. University of Michigan. Retrieved on 2008-03-21.
- Mu-opioid receptor model (inactive state) with antagonist. Retrieved on 2008-03-21.
- Mu-opioid receptor model in active state with agonist. Retrieved on 2008-03-21.
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