title: The third extracellular loop of the human delta-opioid receptor determines the selectivity of delta-opioid agonists.
abstract: In the present study, we replaced the third extracellular loop of the human delta-opioid receptor with that of the human mu-opioid receptor. A modified polymerase chain reaction overlap extension method was used to achieve the exact splicing in the chimera to show the importance of the extracellular loop in ligand binding without interference from transmembrane substitutions. The replacement of the third extracellular loop did not alter the affinity of [3H]diprenorphine but caused a dramatic decrease in the affinity of both the delta-selective peptide agonists cyclo[D-Pen2,4'Cl-Phe4,D-Pen5]enkephalin and deltorphin II and the delta-selective nonpeptide agonists SNC 121 and (-)TAN 67. The affinities of the mu-selective peptide agonist [D-Ala2-MePhe4-Gly-ol5]enkephalin and the mu-preferring nonpeptide agonist morphine were not affected. Site-directed mutagenesis studies show that the mechanism of ligand recognition might be different for each structural class of opioid ligands.
authors.affiliation: Department of Pharmacology, The University of Arizona, College of Medicine, Tucson 85724, USA.
authors.forename: E V
authors.initials: EV
authors.lastname: Varga
authors.forename: X
authors.initials: X
authors.lastname: Li
authors.forename: D
authors.initials: D
authors.lastname: Stropova
authors.forename: T
authors.initials: T
authors.lastname: Zalewska
authors.forename: R S
authors.initials: RS
authors.lastname: Landsman
authors.forename: R J
authors.initials: RJ
authors.lastname: Knapp
authors.forename: E
authors.initials: E
authors.lastname: Malatynska
authors.forename: K
authors.initials: K
authors.lastname: Kawai
authors.forename: A
authors.initials: A
authors.lastname: Mizusura
authors.forename: H
authors.initials: H
authors.lastname: Nagase
authors.forename: S N
authors.initials: SN
authors.lastname: Calderon
authors.forename: K
authors.initials: K
authors.lastname: Rice
authors.forename: V J
authors.initials: VJ
authors.lastname: Hruby
authors.forename: W R
authors.initials: WR
authors.lastname: Roeske
authors.forename: H I
authors.initials: HI
authors.lastname: Yamamura
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D004745:Enkephalins / Q000494:pharmacology; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009842:Oligopeptides / Q000494:pharmacology; D011804:Quinolines / Q000494:pharmacology; D017465:Receptors, Opioid, delta / Q000819:agonists* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000819:agonists / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D004745:Enkephalins; D009842:Oligopeptides; D011804:Quinolines; D017465:Receptors, Opioid, delta; D011993:Recombinant Fusion Proteins; C094142:TAN 67; C064219:enkephalin, Pen(2,5)-4-chloro-Phe(4)-; C060209:deltorphin II, Ala(2)-