Molecular mechanism of G[alpha]i activation by non-GPCR proteins with a G[alpha]-Binding and Activating motif

• Published in: Nature communications Vol. 8; p. 15163
• Main Authors: De Opakua, Alain Ibáñez, Parag-sharma, Kshitij, Digiacomo, Vincent, Merino, Nekane, Leyme, Anthony, Marivin, Arthur, Villate, Maider, Nguyen, Lien T, De La Cruz-morcillo, Miguel Angel, Blanco-canosa, Juan B, Ramachandran, Sekar, Baillie, George S, Cerione, Richard A, Blanco, Francisco J, Garcia-marcos, Mikel
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group 01.05.2017
• Subjects: Biochemistry; NMR; Nuclear magnetic resonance; Proteins; New York; United States > US; Spain
• ISSN: 2041-1723
• DOI: 10.1038/ncomms15163

Heterotrimeric G proteins are quintessential signalling switches activated by nucleotide exchange on Gα. 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 Gα-binding and -activating (GBA) motif. We combine NMR spectroscopy, computational modelling and biochemistry to map changes in Gα caused by binding of GBA proteins with residue-level resolution. We find that the GBA motif binds to the SwitchII/α3 cleft of Gα 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 Gα activation.