Synergistic effect of basic residues at positions 14–15 of nociceptin on binding affinity and receptor activation

[Arg-Lys14-15]nociceptin is a superagonist of the ORL1 receptor. We clarified that the synergistic potentiation occurs only when basic amino acids are simultaneously incorporated. Nociceptin is an endogenous ligand that activates a G protein-coupled receptor ORL1 and contains two indispensable Arg-L...

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Bibliographic Details
Published in:Bioorganic & medicinal chemistry 2008-10, Vol.16 (20), p.9261-9267
Main Authors: Okada, Kazushi, Isozaki, Kaname, Li, Jinglan, Matsushima, Ayami, Nose, Takeru, Costa, Tommaso, Shimohigashi, Yasuyuki
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Animals
Antagonist
Basic amino acids
Biological and medical sciences
Chlorocebus aethiops
COS Cells
Medical sciences
Molecular Sequence Data
Neuropharmacology
Neurotransmitters. Neurotransmission. Receptors
Nociceptin
Nociceptin Receptor
Opioid Peptides - chemical synthesis
Opioid Peptides - chemistry
Opioid Peptides - metabolism
Peptidergic system (neuropeptide, opioid peptide, opiates...). Adenosinergic and purinergic systems
Pharmacology. Drug treatments
Protein Binding
Rats
Receptors, Opioid - genetics
Receptors, Opioid - metabolism
Structure-Activity Relationship
Superagonist
Synergistic potentiation
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Summary:[Arg-Lys14-15]nociceptin is a superagonist of the ORL1 receptor. We clarified that the synergistic potentiation occurs only when basic amino acids are simultaneously incorporated. Nociceptin is an endogenous ligand that activates a G protein-coupled receptor ORL1 and contains two indispensable Arg-Lys (RK) dipeptide units at positions 8–9 and 12–13. By replacing an additional RK unit at positions 6–7, 10–11, 14–15, or 16–17, of the peptide we have identified the analog, [RK 14–15]nociceptin as a superagonist. In fact, this peptide exhibits 3-fold higher binding affinity and 17-fold greater potency in a functional GTPγS-binding assay compared to wild-type nociceptin. Here, we have further investigated the role of basic residues in position 14–15. The replacement of three other possible basic dipeptides, KR, RR, and KK, into nociceptin at positions 14–15 resulted in similar enhancements of binding affinity (3–5-fold) and biological potency (10–12-fold in the GTPγS assay). However, when only a single basic residue (Arg or Lys) was replaced in either position 14 or 15, all the resulting analogs showed moderate enhancements of binding and biological activity (2–4-fold in both). These results indicate that the addition of basic charges in positions 14 and 15 enhance in a synergistic fashion the interaction of nociceptin with the receptor and only the simultaneous presence of two adjacent basic residues yields an optimal effect. This suggests that specific electrostatic interactions between both amino acids present in 14–15 and corresponding residues in the receptor are responsible for the enhancement of nociceptin activity.
ISSN:0968-0896
1464-3391
DOI:10.1016/j.bmc.2008.09.014