Latest pairings

The following are reports of recent pairings of receptors with endogenous or synthetic ligands, which in most cases are a single publication.

2017 | 2015 | 2014 | 2013 | 2012 | 2011 | 2009 | 2008 | 2006 | 2005 | 2004 | 2003


GPR15 & GPR15L (encoded by gene C10ORF99)

Suply T et al. (2017). A natural ligand for the orphan receptor GPR15 modulates lymphocyte recruitment to epithelia.
Sci Signal., 10 (496): eaal0180. DOI: 10.1126/scisignal.aal0180. [Abstract]

Ocón B et al. (2017). A Mucosal and Cutaneous Chemokine Ligand for the Lymphocyte Chemoattractant Receptor GPR15.
Front. Immunol., DOI: 10.3389/fimmu.2017.01111. [Epub ahead of print] [Full text]


Mullican SE et al. (2017). GFRAL is the receptor for GDF15 and the ligand promotes weight loss in mice and nonhuman primates. Nat Med., doi: 10.1038/nm.4392. [Epub ahead of print] [PMID:28846097]

Emmerson PJ et al. (2017). The metabolic effects of GDF15 are mediated by the orphan receptor GFRAL. Nat Med., doi: 10.1038/nm.4393. [Epub ahead of print] [PMID:28846098]

Yang L et al. (2017). GFRAL is the receptor for GDF15 and is required for the anti-obesity effects of the ligand. Nat Med., doi: 10.1038/nm.4394. [Epub ahead of print] [PMID:28846099]

GPR19 & adropin

Comments by Anthony Davenport:

Further report on activation of GPR19 by the peptide hormone, adropin

Rao et al. (1) report in vitro signalling studies with the lysates of cells overexpressing the Energy Homeostasis Associated gene (ENHO) that encodes the peptide hormone adropin, inhibits forskolin increases in cAMP and was replicated by using synthetic adropin (EC50 = 8 nM). GPR19 signals via MAPK/ERK1/2 and the authors suggest may play a role in metastasis by promoting the mesenchymal-epithelial transition (MET) through the ERK/MAPK pathway, thus facilitating colonisation of metastatic breast tumour cells.

This study supports the observation of Stein et al. (2). The authors showed reduction in GPR19 mRNA levels in medial basal hypothalamus of male rats resulted in the loss of the inhibitory effect of adropin on water deprivation-induced thirst.

Interestingly, adropin34-76 was screened in a β-arrestin assay as part of a library of 10,000 compounds against ~80 orphan receptors which included GPR19 but no activity was detected, suggesting the possibility that adropin is more effective in signalling via G-proteins (3).

Further characterisation in pharmacological assays is required to establish adropin as the cognate ligand.

  1. Rao A, Herr DR. 2017. G protein-coupled receptor GPR19 regulates E-cadherin expression and invasion of breast cancer cells. Biochim Biophys Acta. 1864: 1318-1327. [PMID: 28476646]
  2. Stein LM, Yosten GL, Samson WK. 2016. Adropin acts in brain to inhibit water drinking: potential interaction with the orphan G protein-coupled receptor, GPR19. Am J Physiol Regul Integr Comp Physiol. 310: R476-80. [PMID: 26739651]
  3. Southern C, Cook JM, Neetoo-Isseljee Z et al. 2013. Screening β-arrestin recruitment for the identification of natural ligands for orphan G-protein-coupled receptors. J Biomol Screen. 18: 599-609. [PMID: 23396314]


GPR139 & amino acids L-Tryptophan and L-Phenylalanine

Read more here...

Isberg V, Andersen KB, Bisig C et al. (2014). Computer-aided discovery of aromatic l-α-amino acids as agonists of the orphan G protein-coupled receptor GPR139.
J Chem Inf Model. 54: 1553-7. [PMID: 24826842]

Liu C, Bonaventure P, Lee G et al. (2015). GPR139, an Orphan Receptor Highly Enriched in the Habenula and Septum, is Activated by the Essential Amino Acids L-Tryptophan and L-Phenylalanine.
Mol Pharmacol. 88: 911-25. [PMID: 26349500]

SLC38A9 orphan transporter is a lysosomal transporter able to transport 3H-glutamine, and to a lesser extent, 3H-arginine and 3H-asparagine.

Rebsamen M, Pochini L, Stasyk T et al. (2015). SLC38A9 is a component of the lysosomal amino acid sensing machinery that controls mTORC1.
Nature. 519: 477-81. [PMID: 25561175]


GPR126 & Type IV collagen.

Paavola KJ, Sidik H, Zuchero JB, Eckart M, Talbot WS. (2014)
Type IV collagen is an activating ligand for the adhesion G protein-coupled receptor GPR126. Sci Signal. 7: ra76 [PMID: 25118328]


GPR17 & cysteinyl-leukotrienes (CysLTs)/ uracil nucleotides.

Ciana P, Fumagalli M, Trincavelli ML, Verderio C, Rosa P, Lecca D, Ferrario S, Parravicini C, Capra V, Gelosa P, Guerrini U, Belcredito S, Cimino M, Sironi L,Tremoli E, Rovati GE, Martini C, Abbracchio MP. (2006)
The orphan receptor GPR17 identified as a new dual uracil nucleotides/cysteinyl-leukotrienes receptor. EMBO J. 25: 4615-27 [PMID: 16990797]

Update 2013: Initial pairing could not be repeated

Heise CE, O'Dowd BF, Figueroa DJ, Sawyer N, Nguyen T, Im DS, Stocco R, Bellefeuille JN, Abramovitz M, Cheng R, Williams DL Jr, Zeng Z, Liu Q, Ma L, Clements MK, Coulombe N, Liu Y, Austin CP, George SR, O'Neill GP, Metters KM, Lynch KR, Evans JF. (2000)
Pharmacological characterization of the first potent and selective antagonist at the cysteinyl leukotriene 2 (CysLT(2)) receptor. J Biol Chem. 275: 30531-6. [PMID: 10851239]

Wunder F, Tinel H, Kast R, Geerts A, Becker EM, Kolkhof P, Hütter J, Ergüden J, Härter M. (2010)
Characterization of the human cysteinyl leukotriene 2 receptor. Br J Pharmacol. 160: 399-409. [PMID: 20423349]

Qi AD, Harden TK, Nicholas RA. (2013)
Is GPR17 a P2Y/leukotriene receptor? examination of uracil nucleotides, nucleotide sugars, and cysteinyl leukotrienes as agonists of GPR17. J Pharmacol Exp Ther. 347: 38-46. [PMID: 23908386]

Hennen S, Wang H, Peters L, Merten N, Simon K, Spinrath A, Blättermann S, Akkari R, Schrage R, Schröder R, Schulz D, Vermeiren C, Zimmermann K, Kehraus S, Drewke C, Pfeifer A, König GM, Mohr K, Gillard M, Müller CE, Lu QR, Gomeza J, Kostenis E. (2013)
Decoding signaling and function of the orphan G protein-coupled receptor GPR17 with a small-molecule agonist. Sci Signal. 6: ra93. [PMID: 24150254]

See also:

Harden TK. (2013)
Enigmatic GPCR finds a stimulating drug. Sci Signal. 6: pe34. [PMID: 24150253]

GPR171 & BigLEN.

Gomes I, Aryal DK, Wardman JH, Gupta A, Gagnidze K, Rodriguiz RM, Kumar S, Wetsel WC, Pintar JE, Fricker LD, Devi LA. (2013)
GPR171 is a hypothalamic G protein-coupled receptor for BigLEN, a neuropeptide involved in feeding.
Proc Natl Acad Sci U S A. 110: 16211-6. [PMID:24043826]

C3a receptor & VGF derived peptide TLQP-21.

Comments by NC-IUPHAR:
"A recent report concerning a peptide derived from the vgf gene product, TLQP-21, is suggestive of an interaction with C3a receptor in rodents. However, in competition binding assays the affinity of TLQP-21 is comparatively low for a peptide-GPCR interaction, where sub-nanomolar affinities are usual. Further reports characterising this interaction, perhaps also extending the observations to human TLQP-21, are required to formally confirm the ligand/receptor pairing."

Hannedouche S, Beck V, Leighton-Davies J, Beibel M, Roma G, Oakeley EJ, Lannoy V, Bernard J, Hamon J, Barbieri S, Preuss I, Lasbennes MC, Sailer AW, Suply T, Seuwen K, Parker CN, Bassilana F. (2013)
The identification of the C3a Receptor (C3AR1) as the target of the VGF derived peptide TLQP-21 in rodent cells.
J Biol Chem. 288: 27434-43. [PMID:23940034]

GPR146 & proinsulin C-peptide.

Yosten GL, Kolar GR, Redlinger LJ, Samson WK. (2013)
Evidence for an interaction between proinsulin C-peptide and GPR146.
J Endocrinol. 218: B1-8. [PMID:23759446]

GPR37 and GPR37L1 & the neuroprotective and glioprotective factors prosaptide and prosaposin.

Meyer RC, Giddens MM, Schaefer SA, Hall RA. (2013)
GPR37 and GPR37L1 are receptors for the neuroprotective and glioprotective factors prosaptide and prosaposin.
Proc Natl Acad Sci U S A. 110: 9529-34. [PMID:23690594]

MRGPRD & alamandine, a novel endogenous heptapeptide cleaved from angiotensin A by ACE2.

Lautner RQ, Villela DC, Fraga-Silva RA, Silva N, Verano-Braga T, Costa-Fraga F, Jankowski J, Jankowski V, Sousa F, Alzamora A, Soares E, Barbosa C, Kjeldsen F, Oliveira A, Braga J, Savergnini S, Maia G, Peluso AB, Passos-Silva D, Ferreira A, Alves F, Martins A, Raizada M, Paula R, Motta-Santos D, Kemplin F, Pimenta A, Alenina N, Sinisterra R, Bader M, Campagnole-Santos MJ, Santos RA. (2013)
Discovery and characterization of alamandine: a novel component of the Renin-Angiotensin system.
Circ Res. 112: 1104-11 [PMID:23446738]

GPR174 & lysophosphatidylserine.

Sugita K, Yamamura C, Tabata K, Fujita N. (2013)
Expression of orphan G-protein coupled receptor GPR174 in CHO cells induced morphological changes and proliferation delay via increasing intracellular cAMP.
Biochem Biophys Res Commun. 430: 190-5 [PMID:23178570]

Inoue A, Ishiguro J, Kitamura H, Arima N, Okutani M, Shuto A, Higashiyama S, Ohwada T, Arai H, Makide K, Aoki J. (2012)
TGFα shedding assay: an accurate and versatile method for detecting GPCR activation.
Nat Methods. 9: 1021-9 [PMID:22983457]

GPR84 & medium chain free fatty acids.

Confirmation of medium chain fatty acids as ligands at GPR84 and a new surrogate ligand, 6-n-octylaminouracil, a fatty acid nucleobase conjugate.

Suzuki M, Takaishi S, Nagasaki M, Onozawa Y, Iino I, Maeda H, Komai T, Oda T. (2013)
Medium-chain fatty acid sensing receptor, GPR84 is a proinflammatory receptor.
J Biol Chem. 288: 10684-91 [PMID:23449982]

Oxoglutarate receptor (GPR99) & leukotriene E4.

Kanaoka Y, Maekawa A, Austen KF. (2013)
Identification of GPR99 as a potential third cysteinyl leukotriene receptor with a preference for leukotriene E4.
J Biol Chem. 288: 10967-72. [PMID:23504326]

A screen of 10000 ligands against 82 GPCRs confirms pairings of cognate ligands with orphan receptors and identifies novel surrogate ligands

An article published online ahead of print in the Journal of Biomolecular Screening reports the results of screening ~10,000 ligands against eighty-two G protein-coupled receptors, mainly orphans, using the PathHunter β-arrestin recruitment assays. Pairings of cognate ligands with orphan receptors were confirmed and a number of novel surrogate ligands identified.

Southern C, Cook JM, Neetoo-Isseljee Z, Taylor DL, Kettleborough CA, Merritt A, Bassoni DL, Raab WJ, Quinn E, Wehrman TS, Davenport AP, Brown AJ, Green A, Wigglesworth MJ, Rees S. (2013)
Screening β-Arrestin Recruitment for the Identification of Natural Ligands for Orphan G-Protein-Coupled Receptors.
J Biomol Screen. 18: 599-609. [PMID: 23396314]


GPR107 & neuronostatin.

Yosten GL, Redlinger LJ, Samson WK. (2012)
Evidence for an interaction of neuronostatin with the orphan G protein-coupled receptor, GPR107.
Am J Physiol Regul Integr Comp Physiol. 303 (9): R941-9. [PMID: 22933024]


GPR31 & 12-(S)-Hydroxyeicosatetraenoic Acid.

Guo Y, Zhang W, Giroux C, Cai Y, Ekambaram P, Dilly AK, Hsu A, Zhou S, Maddipati KR, Liu J, Joshi S, Tucker SC, Lee MJ, Honn KV. (2011)
Identification of the Orphan G Protein-coupled Receptor GPR31 as a Receptor for 12-(S)-Hydroxyeicosatetraenoic Acid. J Biol Chem. 286 (39): 33832-40. [PMID: 21712392]

GPR56 & collagen, type III, alpha-1 (gene symbol COL3A1).

Luo R, Jeong SJ, Jin Z, Strokes N, Li S, Piao X. (2011)
G protein-coupled receptor 56 and collagen III, a receptor-ligand pair, regulates cortical development and lamination. Proc Natl Acad Sci U S A. 108 (31): 12925-30. [PMID: 21768377]

GPR35 & kynurenic acid/2-acyl lysophosphatidic acid.

Statement by NC-IUPHAR on GPR35

"The original report that kynurenic acid is an agonist of GPR35 (1) has been replicated, but controversy remains as to whether it reaches sufficient tissue concentrations to be the endogenous ligand (2). 2-acyl lysophosphatidic acid has also been proposed as an endogenous ligand (3). Pamoic acid, a synthetic chemical that enables long-acting formulations of numerous drugs, has also been reported to be an agonist (see 4 and commentary in 5)."

  1. Wang J, Simonavicius N, Wu X, Swaminath G, Reagan J, Tian H, Ling L. (2006)
    Kynurenic acid as a ligand for orphan G protein-coupled receptor GPR35. J Biol Chem. 281 (31): 22021-22028. [PMID: 16754668]
  2. Kuc D, Zgrajka W, Parada-Turska J, Urbanik-Sypniewska T, Turski WA. (2008)
    Micromolar concentration of kynurenic acid in rat small intestine. Amino Acids. 35 (2): 503-5. [PMID: 18235993]
  3. Oka S, Ota R, Shima M, Yamashita A, Sugiura T. (2010)
    GPR35 is a novel lysophosphatidic acid receptor. Biochem Biophys Res Commun. 395 (2): 232-7. [PMID: 20361937]
  4. Zhao P, Sharir H, Kapur A, Cowan A, Geller EB, Adler MW, Seltzman HH, Reggio PH, Heynen-Genel S, Sauer M, Chung TD, Bai Y, Chen W, Caron MG, Barak LS, Abood ME. (2010)
    Targeting of the orphan receptor GPR35 by pamoic acid: a potent activator of extracellular signal-regulated kinase and β-arrestin2 with antinociceptive activity. Mol Pharmacol. 78 (4): 560-8. [PMID: 20826425]
  5. Neubig RR. (2010)
    Mind your salts: when the inactive constituent isn't. Mol Pharmacol. 78 (4): 558-9. [PMID: 20651116]

GPR183 (EBI2) & oxysterols.

Statement by NC-IUPHAR on GPR183 (EBI2)

"Two independent reports (1, 2) propose 7α, 25-dihydroxycholesterol (7α,25-OHC) as an endogenous ligand of this receptor. 7α,25-OHC is synthesised from cholesterol by the sequential action of cholesterol 25-hydroxylase (CH25H) and CYP7B1 (25-hydroxycholesterol 7-α-hydroxylase). Consistent with 7α,25-OHC as an endogenous ligand, inhibition of CYP7B1 with clotrimazole reduced the content of 7α,25-OHC in the mouse spleen and mimicked the phenotype of pre-activated B cells from EBI2-deficient mice (2) and mice deficient in CH25H had a similar phenotype to EBI2 knockout mice."

  1. Hannedouche S, Zhang J, Yi T, Shen W, Nguyen D, Pereira JP, Guerini D, Baumgarten BU, Roggo S, Wen B, Knochenmuss R, Noël S, Gessier F, Kelly LM, Vanek M, Laurent S, Preuss I, Miault C, Christen I, Karuna R, Li W, Koo DI, Suply T, Schmedt C, Peters EC, Falchetto R, Katopodis A, Spanka C, Roy MO, Detheux M, Chen YA, Schultz PG, Cho CY, Seuwen K, Cyster JG, Sailer AW. (2011)
    Oxysterols direct immune cell migration via EBI2. Nature. 475 (7357): 524-7. [PMID: 21796212]
  2. Liu C, Yang XV, Wu J, Kuei C, Mani NS, Zhang L, Yu J, Sutton SW, Qin N, Banie H, Karlsson L, Sun S, Lovenberg TW. (2011)
    Oxysterols direct B-cell migration through EBI2. Nature. 475 (7357): 519-23. [PMID: 21796211]


GPR55 & lysophosphatidylinositol.

Oka S, Nakajima K, Yamashita A, Kishimoto S, Sugiura T. (2007)
Identification of GPR55 as a lysophosphatidylinositol receptor. Biochem Biophys Res Commun. 362, 928-34. [PMID: 17765871]

Henstridge CM, Balenga NA, Ford LA, Ross RA, Waldhoer M, Irving AJ. (2009)
The GPR55 ligand L-alpha-lysophosphatidylinositol promotes RhoA-dependent Ca2+ signaling and NFAT activation. FASEB J. 23, 183-93. [PMID: 18757503]

Oka S, Toshida T, Maruyama K, Nakajima K, Yamashita A, Sugiura T. (2009)
2-Arachidonoyl-sn-glycero-3-phosphoinositol: A Possible Natural Ligand for GPR55. J Biochem. 145, 13-20. [PMID: 18845565]

GPR81 & lactate.

Cai TQ, Ren N, Jin L, Cheng K, Kash S, Chen R, Wright SD, Taggart AK, Waters MG. (2008)
Role of GPR81 in lactate-mediated reduction of adipose lipolysis. Biochem Biophys Res Commun. 377, 987-91. [PMID: 18952058]

Liu C, Wu J, Zhu J, Kuei C, Yu J, Shelton J, Sutton SW, Li X, Yun SJ, Mirzadegan T, Mazur C, Kamme F, Lovenberg TW. (2009)
Lactate Inhibits Lipolysis in Fat Cells through Activation of an Orphan G-protein-coupled Receptor, GPR81. J Biol Chem. 284, 2811-22. [PMID: 19047060]


CMKOR1 & CXC chemokines CXCL11 and CXCL12/SDF-1

Statement by NC-IUPHAR on CMKOR1

"A molecule listed in the IUPHAR orphan receptor database as CMKOR1, and originally named RDC1, is now commonly referred to in the literature as CXCR7, on the basis of its clear ability to bind the CXC chemokines CXCL11 and CXCL12/SDF-1 with high affinity. Although reports have suggested that this molecule is able to mediate cellular responses, including chemotaxis and Akt activation, this has not been consistently shown in primary cells. In transfection systems, CXCR7 was reported to form heterodimers with CXCR4 and to modulate CXCL12 signaling. Several studies suggest a role for this receptor in cell growth and survival, and in tumorigenesis, but the underlying signaling pathways remain unknown. The mouse homologue is clearly involved in cardiac valve development and has minor effects on marginal zone B cell localization, but the signaling mechanisms are not defined. The zebrafish homologue is clearly involved in primordial germ cell migration, where the mechanism appears to involve scavenging of CXCL12 leading to formation of CXCL12 gradients. The NC-IUPHAR sub-committee on chemokine receptor nomenclature has concluded that use of the systematic chemokine receptor nomenclature name CXCR7 for this molecule shall remain unofficial until clear evidence of signal transduction mechanisms can be obtained."

For database entry click here


GPR92/LPA5 & lysophosphatidic acid.

Lee CW, Rivera R, Gardell S, Dubin AE, Chun J. (2006)
GPR92 as a new G12/13- and Gq-coupled lysophosphatidic acid receptor that increases cAMP, LPA5. J Biol Chem. 281, 23589-97 [PMID: 16774927]

Kotarsky K, Boketoft A, Bristulf J, Nilsson NE, Norberg A, Hansson S, Owman C, Sillard R, Leeb-Lundberg LM, Olde B (2006)
Lysophosphatidic acid binds to and activates GPR92, a G protein-coupled receptor highly expressed in gastrointestinal lymphocytes. J Pharmacol Exp Ther. 318, 619-28 [PMID: 16651401]

GPR23/LPA4 & lysophosphatidic acid.

Ignatov, A., Robert, J., Gregory-Evans, C., Schaller, H. C. (2006)
GPR23 is a lysophosphatidic acid (LPA) receptor utilizing G(s)-,G(q)/G(i)-mediated calcium signaling and G(12/13)-mediated Rho activation. J Biol Chem. 282, 4310-7. [PMID: 17166850]


Ignatov, A., Robert, J., Gregory-Evans, C., Schaller, H. C. (2006)
RANTES stimulates Ca(2+) mobilization and inositol triphosphate (IP(3)) formation in cells transfected with G protein-coupled receptor 75. Br J Pharmacol. 149, 490-7. [PMID: 17001303]

See also:

Pease, J. E. (2006)
Tails of the unexpected - an atypical receptor for the chemokine RANTES/CCL5 expressed in brain. Br J Pharmacol. 149, 460-2. [PMID: 17001302]

GPR35 & Kynurenic acid.

Wang, J., Simonavicius, N., Wu, X., Swaminath, G., Reagan, J., Tian, H., Ling, L. (2006)
Kynurenic acid as a ligand for orphan G protein-coupled receptor GPR35. J Biol Chem. 281, 22021-22028. [PMID: 16754668]

GPR37 & The neuropeptide head activator (HA)

Rezgaoui, M., Susens, U., Ignatov, A., Gelderblom, M., Glassmeier, G., Franke, I., Urny, J., Imai, Y., Takahashi, R. and Schaller, H. C. (2006)
The neuropeptide head activator is a high-affinity ligand for the orphan G-protein-coupled receptor GPR37. J Cell Sci. 119, 542-549. [PMID: 16443751]

GPR119 & Oleoylethanolamide (OEA)

Overton, H. A., Babbs, A. J., Doel, S. M., Fyfe, M. C., Gardner, L. S., Griffin, G., Jackson, H. C., Procter, M. J., Rasamison, C. M., Tang-Christensen, M., Widdowson, P. S., Williams, G. M. and Reynet, C. (2006)
Deorphanization of a G protein-coupled receptor for oleoylethanolamide and its use in the discovery of small-molecule hypophagic agents. Cell Metab. 3, 167-175. [PMID: 16517404]

RETRACTED: GPR68 & Sphingosylphosphorylcholine

Retraction of:
Xu, Y., Zhu, K., Hong, G., Wu, W., Baudhuin, L. M., Xiao, Y. and Damron, D. S. (2000) Nat Cell Biol. 2, 261-7. [PMID: 10806476]

[No authors listed] (2006)
Retraction. Sphingosylphosphorylcholine is a ligand for ovarian cancer G-protein-coupled receptor 1. Nat Cell Biol. 8, 299. [PMID: 16508674]


GPR120 & Free Fatty Acids.

Hirasawa, A., Tsumaya, K., Awaji, T., Katsuma, S., Adachi, T., Yamada, M., Sugimoto, Y., Miyazaki, S. and Tsujimoto, G. (2005)
Free fatty acids regulate gut incretin glucagon-like peptide-1 secretion through GPR120. Nat Med. 11, 90-94. [PMID: 15619630]

GPR30 & Estrogen

Several groups have confirmed that estrogen is an agonist of this receptor, for database entry click here.

For review see: Filardo, E. J. and Thomas, P. (2005)
GPR30: a seven-transmembrane-spanning estrogen receptor that triggers EGF release. Trends Endocrinol Metab. 16, 362-367. [PMID: 16125968]

GPR39 & Obestatin

Zhang, J. V., Ren, P. G., Avsian-Kretchmer, O., Luo, C. W., Rauch, R., Klein, C. and Hsueh, A. J. (2005)
Obestatin, a peptide encoded by the ghrelin gene, opposes ghrelin's effects on food intake. Science. 310, 996-999. [PMID: 16284174]

Initial pairing could not be repeated

Holst, B., Egerod, K. L., Schild, E., Vickers, S. P., Cheetham, S., Gerlach, L. O., Storjohann, L., Stidsen, C. E., Jones, R. Beck-Sickinger, A. G., Schwartz, T. W. (2007)
GPR39 signaling is stimulated by zinc ions but not by obestatin. Endocrinology 148, 13-20. [PMID: 16959833]

Chartrel N, Alvear-Perez R, Leprince J, Iturrioz X, Reaux-Le Goazigo A, Audinot V, Chomarat P, Coge F, Nosjean O, Rodriguez M, Galizzi JP, Boutin JA, Vaudry H, Llorens-Cortes C. (2007)
Zhang et al. reported that obestatin, a peptide derived from the ghrelin precursor, activated the orphan G protein-coupled receptor GPR39. However, we found that I125-obestatin does not bind GPR39 and observed no effects of obestatin on GPR39-transfected cells in various functional assays (cyclic adenosine monophosphate production, calcium mobilization, and GPR39 internalization). Our results indicate that obestatin is not the cognate ligand for GPR39. Science 315, 766. [PMID: 17289961]

CXCR2 & Macrophage Derived lectin MNCF

Moreno, A. N., Pereira-da-Silva, G., Oliver, C., Jamur, M. C., Panunto-Castelo, A. and Roque-Barreira, M. C. (2005)
The macrophage-derived lectin, MNCF, activates neutrophil migration through a pertussis toxin-sensitive pathway. J. Histochem. Cytochem. 53, 715-723.

CMKLR1 & Resolvin E1 (RvE1) oxygenated product of eicosapentaenoic acid (EPA)

Arita, M., Bianchini, F., Aliberti, J., Sher, A., Chiang, N., Hong, S., Yang, R., Petasis, N. A. and Serhan, C. N. (2005)
Stereochemical assignment, antiinflammatory properties, and receptor for the omega-3 lipid mediator resolvin E1. J Exp Med. 201, 713-722. [PMID: 15753205]


GPR55: Proposed as a cannabinoid receptor but endogenous ligand not yet known.

Drmota, T., Greasley, P. and Groblewski T. (2004)
Screening assays for cannabinoid-ligand-type modulators of GPR55. WIPO patent 074 844


TIG2/chermerin found to be an alternative ligand for CMKLR1.

Meder, W., Wendland, M., Busmann, A., Kutzleb, C., Spodsberg, N., John, H., Richter, R., Schleuder, D., Meyer, M. and Forssmann, W. G. (2003)
Characterization of human circulating TIG2 as a ligand for the orphan receptor ChemR23. FEBS Lett. 555, 495-499. [PMID: 14675762]