title: Oligomerization of mu- and delta-opioid receptors. Generation of novel functional properties.
abstract: The existence of dimers and oligomers for many G protein-coupled receptors has been described by us and others. Since many G protein-coupled receptor subtypes are highly homologous to each other, we examined whether closely related receptors may interact with each other directly and thus have the potential to create novel signaling units. Using mu- and delta-opioid receptors, we show that each receptor expressed individually was pharmacologically distinct and could be visualized following electrophoresis as monomers, homodimers, homotetramers, and higher molecular mass oligomers. When mu- and delta-opioid receptors were coexpressed, the highly selective synthetic agonists for each had reduced potency and altered rank order, whereas endomorphin-1 and Leu-enkephalin had enhanced affinity, suggesting the formation of a novel binding pocket. No heterodimers were visualized in the membranes coexpressing mu- and delta-receptors by the methods available. However, hetero-oligomers were identified by the ability to co-immunoprecipitate mu-receptors with delta-receptors and vice versa using differentially epitope-tagged receptors. In contrast to the individually expressed mu- and delta-receptors, the coexpressed receptors showed insensitivity to pertussis toxin and continued signal transduction, likely due to interaction with a different subtype of G protein. In this study, we provide, for the first time, evidence for the direct interaction of mu- and delta-opioid receptors to form oligomers, with the generation of novel pharmacology and G protein coupling properties.
authors.affiliation: Departments of Pharmacology and Medicine, University of Toronto and the Centre for Addiction and Mental Health, Toronto, Ontario M5S 1A8, Canada. s.george@utoronto.ca
authors.forename: S R
authors.initials: SR
authors.lastname: George
authors.forename: T
authors.initials: T
authors.lastname: Fan
authors.forename: Z
authors.initials: Z
authors.lastname: Xie
authors.forename: R
authors.initials: R
authors.lastname: Tse
authors.forename: V
authors.initials: V
authors.lastname: Tam
authors.forename: G
authors.initials: G
authors.lastname: Varghese
authors.forename: B F
authors.initials: BF
authors.lastname: O'Dowd
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D015153:Blotting, Western; D016466:CHO Cells; D019556:COS Cells; D006224:Cricetinae; D019281:Dimerization; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000378:metabolism; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000378:metabolism; D006150:Guanine Nucleotides / Q000494:pharmacology; D009270:Naloxone / Q000378:metabolism; D037342:Pertussis Toxin; D011108:Polymers / Q000378:metabolism; D011487:Protein Conformation; D051381:Rats; D017465:Receptors, Opioid, delta / Q000235:genetics / Q000378:metabolism*; D017450:Receptors, Opioid, mu / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D006150:Guanine Nucleotides; D011108:Polymers; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D010566:Virulence Factors, Bordetella; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D009270:Naloxone; D020881:Enkephalin, D-Penicillamine (2,5)-; D037342:Pertussis Toxin