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Radioligand-Binding and Molecular-Imaging Techniques for the Quantitative Analysis of Established and Emerging Orphan Receptor Systems

  • Anthony P. Davenport
  • Rhoda E. Kuc
Protocol
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Part of the Methods in Molecular Biology™ book series (MIMB, volume 306)

Abstract

Radioligand binding is widely used to characterize receptors and to determine their anatomical distribution, particularly the superfamily of rhodopsinlike, seven-transmembrane-spanning G protein-coupled receptors (GPCRs). More than 200 receptors that transduce many important physiological processes and are the target for about 50% of all drugs have been identified in this family (1, 2, 3, 4, 5, 6) . A further approx 160 or so ″orphan″ GPCRs have been predicted to exist from the human genome and have mRNA sequences characteristic of 7TM GPCRs, but their endogenous ligands await identification. Most of these receptors have been artificially expressed in cell lines linked to a reporter sys- tem to identify when a ligand binds to the receptor (see  Chapter 2). This ″re- verse pharmacology″ approach continues to be used to screen compounds from existing or new combinatorial libraries of biologically active molecules, and has been very successful. More than 45 receptors have been ″de-orphanized″ or paired with their cognate ligand, with nearly half of these putative endo- genous transmitters turning out to be peptides (see Table 1). The number of pairings continues to increase. It is estimated that about 70 of the remaining orphan receptors could turn out to have a peptidic ligand (3).
Table 1

Orphan Receptors Recently Paired With Their Cognate Peptidic Ligands

Year

Human peptide

Orphan receptor

Ligand source

1995

Nociceptin/Orphanin FQ

ORL-1/OFQ

Porcine brain

1998

Apelin

Apelin/APJ

Bovine stomach

 

Orexin A and B (hypercretin 1+2)

Orexin 1 and 2

Rat brain

 

Prolactin Releasing Peptide (PRrP)

hGRP-3/GPR10

Bovine hypothalamus

1999

Ghrelin (motilin related peptide)

Ghrelin/GHS-R

Rat stomach

 

Melanin concentrating hormone (MCH)

MCHR1

Rat whole brain

 

Motilin

GPR38

Peptide library

 

Tuberoinfundibular peptide 39 (TIP39)

PTH2R

Bovine hypothalamus

 

Urotensin-II

UT/GPR14/SENR

Peptide library

2000

Neuromedin U-25 (NMU25)

FM3 and FM4

Peptide library

 

Neuropeptides FF and AF

NPFF-R1

Bovine brain

2001

Metastin (Kisspeptin-54)

GPR54

Human placenta

 

MCH

MCHR2

Peptide library

 

Urocortin II and I (stresscopins)

CRF2

Peptide library

2002

Relaxin

LGR7 and LGR8

Peptide library

 

Bovine adrenomedullary peptide 22 (BAM-22)

SNSR3 and SNSR4

Peptide library

 

Neuropeptides B and W

GPR7 and GPR8

Peptide library

2003

QRFP43 (P52)

SP9155/GPR103

Genome database

 

Relaxin-3/INSL7

GPR135/SALPR

Porcine brain

See refs. 2 and 3 for further information and citations to original papers.

Keywords

Autoradiographical Image Unlabeled Ligand Saturation Assay Ligand Program Incubation Tray 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Humana Press Inc. 2005

Authors and Affiliations

  • Anthony P. Davenport
    • 1
  • Rhoda E. Kuc
    • 1
  1. 1.Clinical Pharmacology UnitUniversity of Cambridge, Centre for Clinical Investigation, Addenbrooke’s HospitalCambridgeUK

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