Structural modelling and mutation analysis of a nociceptin receptor and its ligand complexes.
We recently modelled and proposed four ligand-bound conformations for a G-protein-coupled receptor, namely, forms I, II, III and IV, based on the 3D structure and functional evidences for rhodopsin. In this study, the same strategy was applied to a human nociceptin receptor (NR), in order to predict ligand-bound receptor structures. Additionally, site-directed mutagenesis studies were carried out to evaluate these structures. A Thr138Ala mutant demonstrated the same affinity for [Phe(1)Psi(CH(2)-NH)Gly(2)]nociceptin(1-13)NH(2) as the wild-type receptor; however, the affinity of this mutant for nociceptin was 20-fold lower than that of the wild type. A Ser223Ala mutation showed the same characteristics as those of the wild type. On the other hand, a Gln280Ala mutation reduced the affinity to nociceptin by more than 60-folds. These results suggested that a change in the conformation of NR following agonist binding did not accompany the rigid-body rotation of the sixth transmembrane segment that was reported for an adrenergic receptor and a kappa-opioid receptor. NR is potently activated not only by nociceptin but also a synthetic peptide, i.e. Ac-RYYRIK-NH(2), although the amino acid sequences of both these ligands are completely different. The model explains why both the ligands activate NR and shows that their receptor-bound conformations have similar 3D structures.
Akuzawa
Natsuyo
N
Department of Nano-Material Systems, Graduate School of Engineering, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma, Japan.
Takeda
Shigeki
S
Ishiguro
Masaji
M
D000409:Alanine / Q000737:chemistry; D004252:DNA Mutational Analysis; D006801:Humans; D006860:Hydrogen Bonding; D021621:Imaging, Three-Dimensional; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D018847:Opioid Peptides / Q000737:chemistry*; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D011957:Receptors, Opioid / Q000737:chemistry / Q000502:physiology*; D012984:Software; D013912:Threonine / Q000737:chemistry; D000094942:Nociceptin Receptor; D000097629:Nociceptin
D000409:Alanine; D008024:Ligands; D018847:Opioid Peptides; D043562:Receptors, G-Protein-Coupled; D011957:Receptors, Opioid; D013912:Threonine; D000094942:Nociceptin Receptor; D000097629:Nociceptin; C000722283:OPRL1 protein, human