de Opakua AI, Parag-Sharma K, DiGiacomo V, Merino N, Leyme A, Marivin A, Villate M, Nguyen LT, de la Cruz-Morcillo MA, Blanco-Canosa JB, Ramachandran S, Baillie GS, Cerione RA, Blanco FJ, Garcia-Marcos M.
Nat Commun 2017 May; 8: 15163.
eterotrimeric G proteins are quintessential signalling switches activated by nucleotide exchange on Galpha. Although activation is predominantly carried out by G-protein-coupled receptors (GPCRs), non-receptor guanine-nucleotide exchange factors (GEFs) have emerged as critical signalling molecules and therapeutic targets. Here we characterize the molecular mechanism of G-protein activation by a family of non-receptor GEFs containing a Galpha-binding and -activating (GBA) motif. We combine NMR spectroscopy, computational modelling and biochemistry to map changes in Galpha caused by binding of GBA proteins with residue-level resolution. We find that the GBA motif binds to the SwitchII/alpha3 cleft of Galpha and induces changes in the G-1/P-loop and G-2 boxes (involved in phosphate binding), but not in the G-4/G-5 boxes (guanine binding). Our findings reveal that G-protein-binding and activation mechanisms are fundamentally different between GBA proteins and GPCRs, and that GEF-mediated perturbation of nucleotide phosphate binding is sufficient for Galpha activation.
PubMed: 28516903. Doi: 10.1038/ncomms15163. free PMC article