Gialpha and Gbeta subunits both define selectivity of G protein activation by alpha2-adrenergic receptors

Proc Natl Acad Sci U S A. 2006 Jan 3;103(1):212-7. doi: 10.1073/pnas.0509763102. Epub 2005 Dec 21.


Previous studies of the specificity of receptor interactions with G protein subunits in living cells have relied on measurements of second messengers or other downstream responses. We have examined the selectivity of interactions between alpha2-adrenergic receptors (alpha2R) and various combinations of Gialpha and Gbeta subunit isoforms by measuring changes in FRET between Gialpha-yellow fluorescent protein and cyan fluorescent protein-Gbeta chimeras in HeLa cells. All combinations of Gialpha1, -2, or -3 with Gbeta1, -2, or -4 were activated to some degree by endogenous alpha2Rs as judged by agonist-dependent decreases in FRET. The degree of G protein activation is determined by the combination of Gialpha and Gbeta subunits rather than by the identity of an individual subunit. RT-PCR analysis and small interfering RNA knockdown of alpha2R subtypes, followed by quantification of radiolabeled antagonist binding, demonstrated that HeLa cells express alpha2a- and alpha2b-adrenergic receptor isoforms in a 2:1 ratio. Increasing receptor number by overexpression of the alpha2aR subtype minimized the differences among coupling preferences for Gialpha and Gbeta isoforms. The molecular properties of each Gialpha, Gbeta, and alpha2-adrenergic receptor subtype influence signaling efficiency for the alpha2-adrenergic receptor-mediated signaling pathway.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Enzyme Activation / physiology
  • Fluorescence Resonance Energy Transfer
  • Fluorescent Dyes
  • GTP-Binding Protein alpha Subunits, Gi-Go / metabolism*
  • GTP-Binding Protein beta Subunits / metabolism*
  • HeLa Cells
  • Humans
  • Microscopy, Fluorescence
  • RNA, Small Interfering / genetics
  • Receptors, Adrenergic, alpha-2 / genetics
  • Receptors, Adrenergic, alpha-2 / metabolism*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Signal Transduction / physiology*
  • Substrate Specificity


  • Fluorescent Dyes
  • GTP-Binding Protein beta Subunits
  • RNA, Small Interfering
  • Receptors, Adrenergic, alpha-2
  • GTP-Binding Protein alpha Subunits, Gi-Go