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Orphan receptor: Wikis


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An orphan receptor is an apparent receptor that has a similar structure to other identified receptors but whose endogenous ligand has not yet been identified. If a ligand for an orphan receptor is later discovered, the receptor is referred to as an "adopted orphan".



Examples of orphan receptors are found in the G protein-coupled receptor (GPCR)[1][2][3] and nuclear receptor[4][5][6] families. GPCR orphan receptors are usually given the name "GPR" followed by a number, for example GPR1. Adopted orphan receptors in the nuclear receptor group include the farnesoid X receptor (FXR), liver X receptor (LXR), and peroxisome proliferator-activated receptor (PPAR).


Historically, receptors were discovered by using ligands to "fish" for their receptors. Hence by definition, these receptors were not orphans. However with modern molecular biology techniques such as screening of cDNA libraries, it becomes possible to identify related receptors based on sequence similarity to known receptors without knowing what their ligands are.


  1. ^ Levoye A, Dam J, Ayoub MA, Guillaume JL, Jockers R (2006). "Do orphan G-protein-coupled receptors have ligand-independent functions? New insights from receptor heterodimers". EMBO Rep 7 (11): 1094–8. doi:10.1038/sj.embor.7400838. PMID 17077864.  
  2. ^ Civelli O, Saito Y, Wang Z, Nothacker HP, Reinscheid RK (2006). "Orphan GPCRs and their ligands". Pharmacol Ther 110 (3): 525–32. doi:10.1016/j.pharmthera.2005.10.001. PMID 16289308.  
  3. ^ Wise A, Jupe SC, Rees S (2004). "The identification of ligands at orphan G-protein coupled receptors.". Annu Rev Pharmacol Toxicol 44 (February): 43–66. doi:10.1146/annurev.pharmtox.44.101802.121419. PMID 14744238.  
  4. ^ Giguère V (October 1999). "Orphan nuclear receptors: from gene to function". Endocr. Rev. 20 (5): 689–725. doi:10.1210/er.20.5.689. PMID 10529899.  
  5. ^ Benoit G, Cooney A, Giguere V, Ingraham H, Lazar M, Muscat G, Perlmann T, Renaud JP, Schwabe J, Sladek F, Tsai MJ, Laudet V (2006). "International Union of Pharmacology. LXVI. Orphan nuclear receptors". Pharmacol Rev 58 (4): 798–836. doi:10.1124/pr.58.4.10. PMID 17132856.  
  6. ^ Shi Y (June 2007). "Orphan nuclear receptors in drug discovery". Drug Discov. Today 12 (11-12): 440–5. doi:10.1016/j.drudis.2007.04.006. PMID 17532527.  

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