Affinity labels as tools for the identification of opioid receptor recognition sites

Philip S Portoghese, Rachid El Kouhen, Ping-Yee Law, Horace H Loh, Bertrand Le Bourdonnec

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

Affinity labels have proven to be useful tools in opioid research. We review experiments carried out with the μ opioid receptor affinity label, β-funaltrexamine (2), that support the concept of different recognition sites for μ opioid agonists and antagonists. The data are interpreted in the context of a dimeric receptor that contains two allosterically coupled binding sites: one that binds endogenous agonist, and the second that functions as an inhibitory modulator of agonism. It is proposed that exogenous antagonists bind selectively to the second site. The first of a new class of affinity labels, PGNA (5), that contains the phthaldehyde moiety attached to an opioid antagonist pharmacophore, is described. This class of ligands has been named 'reporter affinity labels' because covalent association leads to the formation of a fluorescent isoindole that is diagnostic for cross-linking of lysine and cysteine residues. PGNA binds opioid receptors covalently, as suggested by (a) irreversible binding to cloned opioid receptors, (b) irreversible opioid antagonism in the guinea pig ileum preparation, and (c) ultra-long opioid antagonism in mice. Since flow cytometry experiments revealed specific enhancement of fluorescence in cloned mu receptors after a 1 min exposure to 5, it is concluded that covalent binding has occurred via the formation of an isoindole, presumably by cross-linking neighboring lysine and cysteine residues in the vicinity of the receptor recognition site.

Original languageEnglish (US)
Pages (from-to)191-196
Number of pages6
JournalFarmaco
Volume56
Issue number3
DOIs
StatePublished - Apr 1 2001

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Affinity Labels
Opioid Receptors
Opioid Analgesics
Isoindoles
Narcotic Antagonists
Lysine
Cysteine
Flow cytometry
mu Opioid Receptor
Ileum
Modulators
Flow Cytometry
Guinea Pigs
Fluorescence
Experiments
Binding Sites
Ligands
Research

Cite this

Affinity labels as tools for the identification of opioid receptor recognition sites. / Portoghese, Philip S; El Kouhen, Rachid; Law, Ping-Yee; Loh, Horace H; Le Bourdonnec, Bertrand.

In: Farmaco, Vol. 56, No. 3, 01.04.2001, p. 191-196.

Research output: Contribution to journalArticle

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