title: Novel, potent ORL-1 receptor agonist peptides containing alpha-Helix-promoting conformational constraints.
abstract: The ORL-1 receptor has recently been cloned and is implicated in a wide variety of physiological and pathophysiological processes. Toward the goal of elucidating important features of the receptor-bound conformation of the endogenous ligand, nociceptin (NC), several conformationally constrained analogues were prepared. Either alpha-aminoisobutyric acid (Aib) or N-methylalanine (MeAla) were inserted as replacement(s) for Ala7, Ala11, or Ala15 in the native NC sequence (FGGFTGARKSARKLANQ). In vitro assays measuring human ORL-1 receptor affinity (competition binding against [3H] NC), functional potency ([35S]GTP gamma S), and efficacy (as compared to NC) were performed for each new peptide. The receptor affinities of the Aib-containing peptides generally matched NC, showing K(i)'s in the range of 0.1-0.5 nM. By comparison, the receptor affinities of the MeAla-containing peptides were significantly diminished. Peptide 14 (FGGFTG[Aib]RKS[Aib]RKLANQ-NH2), which contains two constrained alanine residues (positions 7 and 11) and a C-terminal amide modification, was found to be a very potent agonist with K(i) = 0.05 nM and EC50 = 0.08 nM in the human ORL-1 assays. The data support a hypothesis that the receptor-bound form of NC might adopt an amphipathic helix in the "address" segment of the sequence.
authors.affiliation: Purdue Pharma L. P., 6 Cedar Brook Drive, Cranbury, New Jersey 08512, USA.
authors.forename: Chongwu
authors.initials: C
authors.lastname: Zhang
authors.forename: Wendy
authors.initials: W
authors.lastname: Miller
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Valenzano
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Kyle
mesh_terms: D000595:Amino Acid Sequence; D001667:Binding, Competitive; D002460:Cell Line; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018847:Opioid Peptides / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D010455:Peptides / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D017433:Protein Structure, Secondary; D011869:Radioligand Assay; D011957:Receptors, Opioid / Q000819:agonists*; D013329:Structure-Activity Relationship; D000094942:Nociceptin Receptor; D000097629:Nociceptin
chemical_list: D018847:Opioid Peptides; D010455:Peptides; D011957:Receptors, Opioid; D000094942:Nociceptin Receptor; D000097629:Nociceptin; C469561:phenylalanyl-glycyl-glycyl-phenylalanyl-threonyl-glycyl-alpha-aminoisobutyryl-arginyl-lysyl-seryl-alpha-aminoisobutyryl-arginyl-lysyl-leucyl-alanyl-asparagyl-qlutaminamide; C000722283:OPRL1 protein, human