The mechanism for ligand activation of the GPCR–G protein complex

Abstract

Significance We report the detailed atomistic mechanism for how molecules such as morphine, dopamine, or epinephrine binding outside of a cell to a G protein–coupled receptor (GPCR) in the cell membrane cause a G protein (GP) bound at the inside of the cell to break apart and signal the cell to influence appetite, anxiety, memory, cognition, learning, and sleep. Most surprising is that the GP binds first to the GPCR to form a precoupled complex that remains at rest until the drug binds to induce the signaling. Most important, it is the precoupled GPCR-GP structure that provides the basis for the design of therapeutics to maximize activity and selectivity.

Dynamic allosteric networks drive adenosine A1receptor activation and G-protein coupling

“…To estimate a reliable energy landscape of the A1R-ADO activation and check the importance of the intermediate state, we relied on metadynamics simulations, a powerful method that has been successfully used to study complex conformational transitions in proteins, [24][25][26] including GPCRs. [12,15] In particular, we performed well-tempered metadynamics (WT-MetaD) simulations using the walkers approach (see Materials and methods). We selected 10 representative structures along the activation pathway sampled in the cMD as starting points for the walker replicas (see Figure S2).…”

“…This fast-conformational transition observed in presence of adenosine may favor the binding and activation of G-proteins. [12, 13] Regarding the activation pathway, the inactive state of TM6 that resembles the inactive X-ray structure progresses towards an intermediate state that is characterized by a rather high TM6 torsion and a modest TM6 opening due to the tight TM3-TM6 energy coupling in the intracellular ends. This results in a torsion in the end of TM6, which is signature of the intermediate conformations.…”

“…Thus, the binding of the G-proteins induces a population shift in A1R towards fully-active conformations, as described previously in other GPCR receptors. [11][12][13][14].…”

“…[8,9] In G-protein coupled receptors (GPCRs), the binding of endogenous agonist in the orthosteric site reshapes the conformational ensemble of a Transmembrane (TM) helix to prime the binding and activation of G-proteins. [10][11][12] The conformational landscapes of GPCRs associated with the receptor activation are complex, with some general principles in common and also receptorspecific differences. [13,14] For many GPCRs it has been observed that (1) inactive and preactive states are in dynamic equilibrium in the apo form, (2) the action of the agonist induce subtle population shifts involving the stabilization of intermediate and pre-active states and/or decreasing their rates of interconversion and (3) the combined action of both, agonist and Gprotein binding stabilizes a more rigid fully-active state.…”

Mechanistic basis of GPCR activation explored by ensemble refinement of crystallographic structures

“…Lastly, growing emphasis is put on delineating the ensemble nature of receptor proteins such as GPCRs in order to understand how their conformational ensembles are shifted between multiple states responsible for downstream signaling by various ligands 23,24 . Numerous biophysical explorations have supported these hypotheses 6,25–34 …”