Dissociation of affinity and efficacy in KOR-3 chimeras

FEBS Lett. 1996 Oct 21;395(2-3):207-10. doi: 10.1016/0014-5793(96)01023-x.


KOR-3 chimeras were constructed in which the first coding exon of KOR-3 was exchanged for the corresponding first coding exon of either MOR-1 (MOR-1/KOR-3) or DOR-1 (DOR-1/KOR-3). All three clones were expressed in CHO cells and characterized with regards to their binding profiles for orphanin FQ/nociceptin (OFQ/N) and a variety of opioids as well as their functional activities in cyclase studies. 125I[Tyr14]OFQ/N labels both KOR-3 (KD 37 pM) and the MOR-1/KOR-3 chimera (KD 39 pM) equally well. Although its affinity for the DOR-1/KOR-3 chimera is quite good (KD 135 pM), it is slightly lower than the other two. Competition studies confirm the high affinity of OFQ/N for all three clones. However, several competitors clearly distinguish the chimeras from KOR-3. OFQ/N(1-11) competes KOR-3 (Ki 55 nM) over 6-fold more potently than either of the chimeras. (Ki values > 350 nM). Conversely, the modest affinity of naloxone benzoylhydrazone for KOR-3 (310 nM) is greatly increased in both the MOR-1/KOR-3 (Ki 69 nM) and DOR-1/KOR-3 (Ki 74 nM) chimeras. The remainder of the opioids tested have no appreciable affinity against any of the clones. Functionally, OFQ/N inhibits forskolin-stimulated cAMP accumulation in both the KOR-3 and the MOR-1/KOR-3 chimera by almost 40%, with IC50 values in the low nanomolar range. Little activity is seen against the DOR-1/KOR-3 chimera. Naloxone benzoylhydrazone inhibits cAMP accumulation in the KOR-3 and the DOR-1/KOR-3 chimera. Although naloxone benzoylhydrazone has higher affinity for the MOR-1/KOR-3 chimera in binding studies than KOR-3 itself, it is inactive in cyclase studies using the MOR-1/KOR-3 chimera, implying that the replacement of the first coding exon increases affinity while decreasing intrinsic activity.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Base Sequence
  • CHO Cells
  • Colforsin / pharmacology
  • Cricetinae
  • Cyclic AMP / metabolism
  • DNA Primers
  • Exons
  • Kinetics
  • Mice
  • Models, Structural
  • Narcotics / metabolism
  • Narcotics / pharmacology
  • Nerve Tissue Proteins / biosynthesis
  • Nerve Tissue Proteins / chemistry*
  • Nerve Tissue Proteins / metabolism*
  • Nociceptin
  • Nociceptin Receptor
  • Opioid Peptides / metabolism
  • Polymerase Chain Reaction
  • Protein Structure, Secondary*
  • Receptors, Opioid*
  • Receptors, Opioid, kappa / biosynthesis
  • Receptors, Opioid, kappa / metabolism*
  • Recombinant Fusion Proteins / biosynthesis
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / metabolism*
  • Restriction Mapping
  • Transfection


  • DNA Primers
  • Narcotics
  • Nerve Tissue Proteins
  • Opioid Peptides
  • Receptors, Opioid
  • Receptors, Opioid, kappa
  • Recombinant Fusion Proteins
  • Colforsin
  • Cyclic AMP
  • Nociceptin Receptor