The Role of a Conserved Inter-Transmembrane Domain Interface in Regulating α2a-Adrenergic Receptor Conformational Stability and Cell-Surface Turnover

  1. Matthew H. Wilson,
  2. Hilary A. Highfield and
  3. Lee E. Limbird
  1. Department of Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee

    Abstract

    Functional and structural data from G protein-coupled receptors (GPCR) predict that transmembrane-domain (TM)2 is adjacent to TM7 within the GPCR structure, and that within this interface a conserved aspartate in TM2 and a conserved asparagine in TM7 exist in close proximity. Mutation at this D79(TM2)-N422(TM7) interface in the α2A-adrenergic receptor (α2AAR) affects not only receptor activation but also cell-surface residence time and conformational stability. Mutation at TM2(D79N) reduces allosteric modulation by Na+ and receptor activation more dramatically than affecting cell-surface receptor turnover and conformational stability, whereas mutation at TM7(N422D) creates profound conformational instability and more rapid degradation of receptor from the surface of cells despite receptor activation and allosteric modulation properties that mirror a wild-type receptor. Double mutation of TM2 and 7(D79N/N422D) reveals phenotypes for receptor activation and conformational stability intermediate between the wild-type and singly mutated α2AAR. Additionally, the structural placement of a negative charge at this TM2/TM7 interface is necessary but not sufficient for receptor structural stability, because mislocalization of the negative charge in either the D79Eα2AAR (which extends the charge out one methylene group) or the D79N/N422Dα2AAR (placing the charge in TM7 instead of TM2) results in conformational lability in detergent solution and more rapid cell-surface receptor clearance. These studies suggest that this interface is important in regulating receptor cell-surface residence time and conformational stability in addition to its previously recognized role in receptor activation.

    Footnotes

    • Send reprint requests to: Dr. Lee E. Limbird, Department of Pharmacology, 468 MRB I, Vanderbilt University Medical Center, Nashville, Tennessee. E-mail:lee.limbird{at}mcmail.vanderbilt.edu

    • This work was supported by National Institutes of Health Grant HL43671 to L.E.L. and Medical Scientist Training Program Grant GM07347 for M.H.W.

    • Abbreviations:
      α2AR
      α2-adrenergic receptor
      GPCR
      G protein-coupled receptors(s)
      TM
      transmembrane domain
      MAP
      mitogen activated protein
      GnRH
      gonadotropin-releasing hormone
      HA
      hemagglutinin
      CHO
      Chinese hamster ovary
      EcR
      ecdysone receptor-expressing
      HEK
      human embryonic kidney
      FCS
      fetal calf serum
      PMSF
      phenylmethylsulfonyl fluoride
      [125I]PIC
      para-[125I]iodoclonidine
      GppNHp
      5′-guanylylimidodiphosphate
      WT
      wild-type
      PAGE
      polyacrylamide gel electrophoresis
      DβM/CHS
      dodecyl-β-d-maltoside/cholesteryl hemisuccinate
      CAPS
      3-(cyclohexylamino)propanesulfonic acid
      t1/2
      half-life
      • Received October 16, 2000.
      • Accepted January 3, 2001.
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    This Article

    1. Molecular Pharmacology April 1, 2001 vol. 59 no. 4 929-938
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