Opioid receptor
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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).
Types of receptors
There are three major subtypes of opioid receptors: [1]
| Greek letter name | Name based on order of discovery | Subtypes |
| delta Opioid receptor (δ) | OP1 | δ1, δ2 |
| kappa Opioid receptor (κ) | OP2 | κ1, κ2, κ3 |
| mu Opioid receptor (μ) | OP3 | μ1, μ2, μ3 |
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.[1]
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.[1]
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 subcommittee has suggested that appropriate terminology for the 3 typical (μ, δ, κ) and the atypical (nociceptin) receptors, should be MOR, DOR, KOR and NOR respectively.
References
See also
External links
- IUPHAR GPCR Database - Opioid Receptors
- MeSH Opioid+Receptors
- Calculated spatial position of mu-opioid receptor in the lipid bilayer, inactive state with antagonist and active state with agonist
Neuropeptide receptors | |
|---|---|
| Hypothalamic hormone receptors | CRH - FSH - LHRH - TRH - Somatostatin |
| Pituitary hormone receptors | Vasopressin (1A, 1B, 2) - Oxytocin - LHCG - Type I cytokine receptor (GH, Prolactin) - TSH |
| Other hormone receptors | Atrial natriuretic factor - Calcitonin - Cholecystokinin (A, B) - VIP |
| Opioid receptors | Delta - Kappa - Mu - Sigma (1, 2) - Nociceptin |
| Other neuropeptide receptors | Angiotensin - Bradykinin (B1, B2) / Tachykinin (TACR1) - Calcitonin gene-related peptide - Galanin - GPCR neuropeptide (B/W, FF, S, Y) - Neurotensin |
fr:Récepteur opiacé fi:Opioidireseptori
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
