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 language | English (US) |
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Pages (from-to) | 2920-2927 |
Number of pages | 8 |
Journal | FASEB Journal |
Volume | 22 |
Issue number | 8 |
DOIs | |
State | Published - Aug 2008 |
Keywords
- Collision
- FRAP
- Heterotrimers
- Precoupling
ASJC Scopus subject areas
- Biotechnology
- Biochemistry
- Molecular Biology
- Genetics