title: Palmitoylation and membrane cholesterol stabilize μ-opioid receptor homodimerization and G protein coupling.
abstract: BACKGROUND
  A cholesterol-palmitoyl interaction has been reported to occur in the dimeric interface of the β₂-adrenergic receptor crystal structure. We sought to investigate whether a similar phenomenon could be observed with μ-opioid receptor (OPRM1), and if so, to assess the role of cholesterol in this class of G protein-coupled receptor (GPCR) signaling.
  
  
  RESULTS
  C3.55(170) was determined to be the palmitoylation site of OPRM1. Mutation of this Cys to Ala did not affect the binding of agonists, but attenuated receptor signaling and decreased cholesterol associated with the receptor signaling complex. In addition, both attenuation of receptor palmitoylation (by mutation of C3.55[170] to Ala) and inhibition of cholesterol synthesis (by treating the cells with simvastatin, a HMG-CoA reductase inhibitor) impaired receptor signaling, possibly by decreasing receptor homodimerization and Gαi2 coupling; this was demonstrated by co-immunoprecipitation, immunofluorescence colocalization and fluorescence resonance energy transfer (FRET) analyses. A computational model of the OPRM1 homodimer structure indicated that a specific cholesterol-palmitoyl interaction can facilitate OPRM1 homodimerization at the TMH4-TMH4 interface.
  
  
  CONCLUSIONS
  We demonstrate that C3.55(170) is the palmitoylation site of OPRM1 and identify a cholesterol-palmitoyl interaction in the OPRM1 complex. Our findings suggest that this interaction contributes to OPRM1 signaling by facilitating receptor homodimerization and G protein coupling. This conclusion is supported by computational modeling of the OPRM1 homodimer.
authors.affiliation: Department of Pharmacology, University of Minnesota, Minneapolis, Minnesota 55455, USA. zhenhui2055@hotmail.com
authors.forename: Hui
authors.initials: H
authors.lastname: Zheng
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Pearsall
authors.forename: Dow P
authors.initials: DP
authors.lastname: Hurst
authors.forename: Yuhan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Ji
authors.initials: J
authors.lastname: Chu
authors.forename: Yali
authors.initials: Y
authors.lastname: Zhou
authors.forename: Patricia H
authors.initials: PH
authors.lastname: Reggio
authors.forename: Horace H
authors.initials: HH
authors.lastname: Loh
authors.forename: Ping-Yee
authors.initials: PY
authors.lastname: Law
mesh_terms: D002784:Cholesterol / Q000378:metabolism*; D003545:Cysteine / Q000378:metabolism; D051960:GTP-Binding Protein alpha Subunit, Gi2 / Q000378:metabolism*; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000378:metabolism; D054878:Lipoylation / Q000502:physiology; D010766:Phosphorylation / Q000502:physiology; D055503:Protein Multimerization / Q000502:physiology; D017450:Receptors, Opioid, mu / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology
chemical_list: D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D017450:Receptors, Opioid, mu; D002784:Cholesterol; D051960:GTP-Binding Protein alpha Subunit, Gi2; D003545:Cysteine