Abstract
To understand how two structurally analogous ligand-receptor systems, the nociceptin/opioid receptor-like 1 (ORL1) and dynorphin A/κ-opioid receptor 1 (KOR1) systems, achieve selectivity, receptor chimeras were generated and analyzed. Replacing discrete domains located between the N-terminus and top of the third transmembrane helix of the KOR1 by the homologous domains of the ORL1 receptor yields hybrid receptors, which, in comparison with the parent KOR1, display up to 300-fold increased affinity but low sensitivity toward nociceptin, and unaltered (high) affinity and sensitivity toward dynorphin A. These substitutions contribute elements for binding of nociceptin but do not suppress determinants necessary for binding and potency of dynorphin A. More importantly, further replacement in these chimeras of the second extracellular loop with that of the ORL1 receptor fully restores responsiveness to nociceptin without impairing responsiveness to dynorphin A. A bifunctional hybrid receptor has thus been identified that binds and responds to both nociceptin and dynorphin A as efficiently as the ORL1 receptor does to nociceptin and the KOR1 to dynorphin A. Together, these results suggest that distinct peptide activation mechanisms operate in the two receptor systems. In particular, the second extracellular receptor loop appears to be an absolute requirement for activation of the ORL1 receptor by nociceptin, but not for activation of the KOR1 by dynorphin A.
Footnotes
- Received September 2, 1998.
- Accepted November 16, 1998.
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Send reprint requests to: Dr. Jean-Claude Meunier, Institut de Pharmacologie et de Biologie Structurale, Centre National de la Recherche Scientifique (CNRS) UPR 9062, 205 route de Narbonne, 31077 Toulouse cédex 4, France. E-mail:jcm{at}ipbs.fr
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C. Mollereau and L. Moulédous contributed equally to this work and thus should be regarded as joint first authors. This work was supported by the Association pour la Recherche sur le Cancer (ARC, Grants 1048 and 9428), the Ministère de l’Education Nationale, de la Recherche et de la Technologie (MENRT, Grant ACC-SV5 9505099), and the European Commission (Biomed 2 program, Grant BMH4 CT97 2317).
- The American Society for Pharmacology and Experimental Therapeutics
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