title: Beta2-adrenergic receptor homodimers: Role of transmembrane domain 1 and helix 8 in dimerization and cell surface expression.
abstract: Even though there are hundreds of reports in the published literature supporting the hypothesis that G protein-coupled receptors (GPCR) form and function as dimers this remains a highly controversial area of research and mechanisms governing homodimer formation are poorly understood. Crystal structures revealing homodimers have been reported for many different GPCR. For adrenergic receptors, a potential dimer interface involving transmembrane domain 1 (TMD1) and helix 8 (H8) was identified in crystal structures of the beta1-adrenergic (β1-AR) and β2-AR. The purpose of this study was to investigate a potential role for TMD1 and H8 in dimerization and plasma membrane expression of functional β2-AR. Charged residues at the base of TMD1 and in the distal portion of H8 were replaced, singly and in combination, with non-polar residues or residues of opposite charge. Wild type and mutant β2-AR, tagged with YFP and expressed in HEK293 cells, were evaluated for plasma membrane expression and function. Homodimer formation was evaluated using bioluminescence resonance energy transfer, bimolecular fluorescence complementation, and fluorescence correlation spectroscopy. Amino acid substitutions at the base of TMD1 and in the distal portion of H8 disrupted homodimer formation and caused receptors to be retained in the endoplasmic reticulum. Mutations in the proximal region of H8 did not disrupt dimerization but did interfere with plasma membrane expression. This study provides biophysical evidence linking a potential TMD1/H8 interface with ER export and the expression of functional β2-AR on the plasma membrane. This article is part of a Special Issue entitled: Interactions between membrane receptors in cellular membranes edited by Kalina Hristova.
authors.affiliation: Department of Neuroscience and Experimental Therapeutics, Albany Medical College, 47 New Scotland Ave., Albany, NY 12208, United States. Electronic address: v.parmar@neurosurgery.wisc.edu.
authors.forename: Vikas K
authors.initials: VK
authors.lastname: Parmar
authors.affiliation: Department of Neuroscience and Experimental Therapeutics, Albany Medical College, 47 New Scotland Ave., Albany, NY 12208, United States.
authors.forename: Ellinor
authors.initials: E
authors.lastname: Grinde
authors.affiliation: Department of Neuroscience and Experimental Therapeutics, Albany Medical College, 47 New Scotland Ave., Albany, NY 12208, United States.
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Mazurkiewicz
authors.affiliation: Department of Neuroscience and Experimental Therapeutics, Albany Medical College, 47 New Scotland Ave., Albany, NY 12208, United States. Electronic address: daviskh@mail.amc.edu.
authors.forename: Katharine
authors.initials: K
authors.lastname: Herrick-Davis
mesh_terms: D002462:Cell Membrane / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018360:Crystallography, X-Ray; D004721:Endoplasmic Reticulum / Q000737:chemistry / Q000235:genetics; D005786:Gene Expression Regulation / Q000235:genetics; D057809:HEK293 Cells; D006801:Humans; D009154:Mutation; D011487:Protein Conformation; D000072417:Protein Domains / Q000235:genetics; D055503:Protein Multimerization / Q000235:genetics*; D018342:Receptors, Adrenergic, beta-1 / Q000737:chemistry* / Q000235:genetics; D018343:Receptors, Adrenergic, beta-2 / Q000737:chemistry* / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics; D013050:Spectrometry, Fluorescence
chemical_list: D018342:Receptors, Adrenergic, beta-1; D018343:Receptors, Adrenergic, beta-2
keywords: Beta(2)-adrenergic receptor; Dimerization; Fluorescence correlation spectroscopy; Homodimer interface; Trafficking