title: The NMR-derived conformation of orexin-A: an orphan G-protein coupled receptor agonist involved in appetite regulation and sleep.
abstract: The conformation of orexin-A, an orphan G-protein coupled receptor agonist has been determined when bound to sodium dodecylsulphate-d(25) (SDS) micelles by (1)H and (13)C NMR and molecular modeling. Orexin-A has been implicated in sleep-wakefulness and feeding regulation. The conformational preference of orexin-A consists of a short helical section, involving Asp(5) to Gln(9) that makes up helix I, followed by a bend from Lys(10) to Ser(13). Residues Leu(16) to Gly(22) make up helix II. The conformation of orexin-A can now be used to explain the results of earlier Ala substitution mutagenesis experiments (J. G. Darker et al., Bioorg. Med. Chem. Lett. 11, 737-740 (2001); S. Ammoun, et al., J. Pharmacol. Expt. Ther. 305, 507-514 (2003)). Darker et al., working with orexin-A (15-33) amide, observed a significant drop in functional potency at the OX(1)R receptor when Leu(16), Leu(19), Leu(20), His(26), Gly(29), Ile(30), Leu(31), Thr(32), and Leu(33) were replaced by Ala. Ammoun et al. identified three areas of interest, which were the same for OX(1)R and OX(2)R receptors, as amino acids 15-17, 20 and 25-26 with the most marked reduction in activity being produced by the replacement of Leu(20) by Ala. We suggest that Leu(16), Leu(19), and Leu(20), which are in helix II, are likely responsible for binding orexin-A to the surface of the micelle.
authors.affiliation: Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G Canada. george.kotovych@ualberta.ca
authors.forename: Mark
authors.initials: M
authors.lastname: Miskolzie
authors.forename: George
authors.initials: G
authors.lastname: Kotovych
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001069:Appetite Regulation / Q000502:physiology*; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D008823:Micelles; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009479:Neuropeptides / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular; D064446:Orexin Receptors; D000068797:Orexins; D011487:Protein Conformation; D043562:Receptors, G-Protein-Coupled / Q000819:agonists*; D018013:Receptors, Neuropeptide; D016415:Sequence Alignment; D012890:Sleep / Q000502:physiology*; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D013501:Surface-Active Agents / Q000737:chemistry
chemical_list: D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008823:Micelles; D009479:Neuropeptides; D064446:Orexin Receptors; D000068797:Orexins; D043562:Receptors, G-Protein-Coupled; D018013:Receptors, Neuropeptide; D013501:Surface-Active Agents; D012967:Sodium Dodecyl Sulfate