Giα and Gβ subunits both define selectivity of G protein activation by α2-adrenergic receptors

Scott K. Gibson, Alfred G. Gilman

Research output: Contribution to journalArticlepeer-review

106 Scopus citations


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 α2-adrenergic receptors (α2R) and various combinations of Giα and Gβ subunit isoforms by measuring changes in FRET between Giα-yellow fluorescent protein and cyan fluorescent protein-Gβ chimeras in HeLa cells. All combinations of Giα1, -2, or -3 with Gβ1, -2, or -4 were activated to some degree by endogenous α2Rs as judged by agonist-dependent decreases in FRET. The degree of G protein activation is determined by the combination of Giα and Gβ subunits rather than by the identity of an individual subunit. RT-PCR analysis and small interfering RNA knockdown of α2R subtypes, followed by quantification of radiolabeled antagonist binding, demonstrated that HeLa cells express α2a- and α2b-adrenergic receptor isoforms in a 2:1 ratio. Increasing receptor number by overexpression of the α2aR subtype minimized the differences among coupling preferences for Giα and Gβ isoforms. The molecular properties of each Giα, Gβ, and α2-adrenergic receptor subtype influence signaling efficiency for the α2-adrenergic receptor-mediated signaling pathway.

Original languageEnglish (US)
Pages (from-to)212-217
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number1
StatePublished - Jan 3 2006


  • Fluorescence resonance energy transfer
  • GTP-binding protein α subunits
  • GTP-binding protein β subunits
  • Small interfering RNA

ASJC Scopus subject areas

  • General


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