Creating a Functional Opioid Alkaloid Binding Site in the Orphanin FQ Receptor through Site-Directed Mutagenesis
Although much has been learned about the mechanisms of ligand selectivity between different opioid receptor subtypes, little is known about the common opioid binding pocket shared by all opioid receptors. The recently discovered orphanin system offers a good opportunity to study the mechanisms invol...
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Veröffentlicht in: | Molecular pharmacology 1998-04, Vol.53 (4), p.772-777 |
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Zusammenfassung: | Although much has been learned about the mechanisms of ligand selectivity between different opioid receptor subtypes, little
is known about the common opioid binding pocket shared by all opioid receptors. The recently discovered orphanin system offers
a good opportunity to study the mechanisms involved in the binding of opioid versus nonopioid ligands. In the current study,
we adopt a âgain of functionâ approach aimed at shifting the binding profile of the orphanin FQ receptor toward that of the
opioid receptors. After two rounds of mutagenesis, several orphanin FQ receptor mutants can be labeled with the opiate alkaloid
[ 3 H]naltrindole and show greatly increased affinities toward the opiate antagonists naltrexone, nor-binaltrophine HCl, and (â)-bremazocine.
These orphanin FQ receptor mutants also display stereospecificity similar to that of opioid receptors. Furthermore, the orphanin
FQ receptor mutant that has the best affinities toward the opioid alkaloids shows, in the presence of GTP and high salt concentration,
an affinity-shift profile similar to that of the δ receptor. Most strikingly, the same mutant exhibits naltrindole-sensitive
etorphine-stimulated [ 35 S]guanosine-5â²- O -(3-thio)triphosphate binding, whereas the effect of etorphine on GTP binding cannot be inhibited by naltrindole in the wild-type
receptor. Our results indicate that 1) several residues in the orphanin FQ receptor are critical to its selectivity against
the opiate alkaloids, particularly antagonists; and 2) mutating these residues to those of the opioid receptor at the corresponding
position preserves the agonist/antagonist nature of opiate alkaloids as they interact with the mutant receptor. It is reasonable
to hypothesize that the corresponding residues in the opioid receptors may form a functional common binding pocket for opiate
alkaloids. These findings may be helpful to medicinal chemists in designing ligands for the orphanin FQ receptor based on
the structure of the opiate alkaloids. |
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ISSN: | 0026-895X 1521-0111 |
DOI: | 10.1124/mol.53.4.772 |