Analysis of selective binding epitopes for the κ-opioid receptor antagonist nor-binaltorphimine

S. A. Hjorth, K. Thirstrup, D. K. Grandy, T. W. Schwartz

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    The structural determinants for the selective binding of the nonpeptide opioid receptor antagonist nor-binaltorphimine (nor-BNI) to the ≃-opioid receptor were characterized using a systematic series of chimeras between the ≃ receptor and the homologous μ-opioid receptor. All 10 chimeric constructs bound the nonselective antagonists (-)-naloxone and diprenorphine with similar affinities, as did the two wild-type receptors. Introduction of amino-terminal segments of increasing length, extending to and including transmembrane segment VI, from the μ receptor into the ≃ receptor did not impair the high affinity binding of nor-BNI, and neither did introduction of the intracellular carboxyl-terminal extension of the μ receptor. In contrast, nor-BNI binding was impaired ≥600-fold in constructs in which extracellular loop 3 and transmembrane segment VII originated from the μ receptor. The exchange of a single residue within this region, Glu297, for lysine, the corresponding residue from the μ receptor, reduced the binding affinity of nor-BNI 142-fold, without affecting the binding of the nonselective compounds (-)-naloxone and diprenorphine. It is concluded that the selective binding of nor-BNI to the ≃-opioid receptor is determined by nonconserved residues located in extracellular loop 3 and transmembrane segment VII and that Glu297, located just outside transmembrane segment VI, plays a major role in the ≃-selective binding characteristics of nor- BNI.

    Original languageEnglish (US)
    Pages (from-to)1089-1094
    Number of pages6
    JournalMolecular pharmacology
    Issue number6
    StatePublished - Jan 1 1995


    ASJC Scopus subject areas

    • Molecular Medicine
    • Pharmacology

    Cite this

    Hjorth, S. A., Thirstrup, K., Grandy, D. K., & Schwartz, T. W. (1995). Analysis of selective binding epitopes for the κ-opioid receptor antagonist nor-binaltorphimine. Molecular pharmacology, 47(6), 1089-1094.