Abundance and stability of complexes containing inactive G protein-coupled receptors and G proteins

Kou Qin, Pooja R. Sethi, Nevin A. Lambert

Research output: Contribution to journalArticle

44 Scopus citations

Abstract

G protein-coupled receptors (GPCRs) interact directly with heterotrimeric G proteins to transduce physiological signals. Early studies of this interaction concluded that GPCRs (R) and G proteins (G) collide with each other randomly after receptor activation and that R-G complexes are transient. More recent studies have suggested that inactive R and G are preassembled (precoupled) as stable R-G complexes. Here we examine the stability of complexes formed between cyan fluorescent protein-labeled α2A-adrenoreceptors (C-α2ARs) and G proteins in cells using fluorescence recovery after photobleaching (FRAP). Labeled G proteins diffused in the plasma membrane with equal mobility in the absence and presence of immobile C-α2ARs. Immobile C-α2ARs activated labeled G proteins, demonstrating functional coupling without stable physical association. In contrast, a stable R-G interaction was detected when G proteins were deprived of nucleotides and C-α2ARs were active, as predicted by the ternary complex model. Overexpression of regulator of G protein signaling 4 (RGS4) accelerated the onset of effector activation but did not detectably alter the interaction between C-α2ARs and G proteins. We conclude that at most a small fraction of C-α2ARs and G proteins exist as R-G complexes at any moment.

Original languageEnglish (US)
Pages (from-to)2920-2927
Number of pages8
JournalFASEB Journal
Volume22
Issue number8
DOIs
StatePublished - Aug 2008

Keywords

  • Collision
  • FRAP
  • Heterotrimers
  • Precoupling

ASJC Scopus subject areas

  • Biotechnology
  • Biochemistry
  • Molecular Biology
  • Genetics

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