Batebi, Hossein; Guillermo Perez-Hernandez; Sabrina N. Rahman; Baoliang Lan; Antje Kamprad; Mingyu Shi; David Speck; Johanna K. S. Tiemann; Ramon Guixa-Gonzalez; Franziska Reinhardt; Peter F. Stadler; Makaia M. Papasergi-Scott; Georgios Skiniottis; Patrick Scheerer; Brain K. Kobilka; Jesper M. Mathiesen; Xiangyu Liu and Peter W. Hildebrand
G-protein-coupled receptors (GPCRs) activate heterotrimeric G proteins by promoting guanine nucleotide exchange. Here, we investigate the coupling of G proteins with GPCRs and describe the events that ultimately lead to the ejection of GDP from its binding pocket in the G alpha subunit, the rate-limiting step during G-protein activation. Using molecular dynamics simulations, we investigate the temporal progression of structural rearrangements of GDP-bound Gs protein (GsGDP; hereafter GsGDP) upon coupling to the beta 2-adrenergic receptor (beta 2AR) in atomic detail. The binding of GsGDP to the beta 2AR is followed by long-range allosteric effects that significantly reduce the energy needed for GDP release: the opening of alpha 1-alpha F helices, the displacement of the alpha G helix and the opening of the alpha-helical domain. Signal propagation to the Gs occurs through an extended receptor interface, including a lysine-rich motif at the intracellular end of a kinked transmembrane helix 6, which was confirmed by site-directed mutagenesis and functional assays. From this beta 2AR-GsGDP intermediate, Gs undergoes an in-plane rotation along the receptor axis to approach the beta 2AR-Gsempty state. The simulations shed light on how the structural elements at the receptor-G-protein interface may interact to transmit the signal over 30 & Aring; to the nucleotide-binding site. Our analysis extends the current limited view of nucleotide-free snapshots to include additional states and structural features responsible for signaling and G-protein coupling specificity.