Mapping the conformational landscape of the stimulatory heterotrimeric G protein (Nature Structural & Molecular Biology)
Heterotrimeric G proteins serve as membrane-associated signaling hubs, in concert with their cognate G-protein-coupled receptors. Fluorine nuclear magnetic resonance spectroscopy was employed to monitor the conformational equilibria of the human stimulatory G-protein alpha subunit (G(s)alpha) alone, in the intact G(s)alpha beta(1)gamma(2) heterotrimer or in complex with membrane-embedded human adenosine A(2A) receptor (A(2A)R).The results reveal a concerted equilibrium that is strongly affected by nucleotide and interactions with the beta gamma subunit, the lipid bilayer and A(2A)R. The alpha 1 helix of G(s)alpha exhibits significant intermediate timescale dynamics. The alpha 4 beta 6 loop and alpha 5 helix undergo membrane/receptor interactions and order-disorder transitions respectively, associated with G-protein activation. The alpha N helix adopts a key functional state that serves as an allosteric conduit between the beta gamma subunit and receptor, while a significant fraction of the ensemble remains tethered to the membrane and receptor upon activation.
Fluorine nuclear magnetic resonance spectroscopy of the stimulatory heterotrimeric G protein reveals a conformational landscape shaped by interactions with nucleotides, the lipid bilayer and a G-protein-coupled receptor.