Potent and Selective Peptide-based Inhibition of the G Protein Gαq.

In contrast to G protein-coupled receptors, for which chemical and peptidic inhibitors have been extensively explored, few compounds are available that directly modulate heterotrimeric G proteins. Active Gα _q binds its two major classes of effectors, the phospholipase C (PLC)-β isozymes and Rho guanine nucleotide exchange factors (RhoGEFs) related to Trio, in a strikingly similar fashion: a continuous helix-turn-helix of the effectors engages Gα _q within its canonical binding site consisting of a groove formed between switch II and helix α3. This information was exploited to synthesize peptides that bound active Gα _q in vitro with affinities similar to full-length effectors and directly competed with effectors for engagement of Gα _q A representative peptide was specific for active Gα _q because it did not bind inactive Gα _q or other classes of active Gα subunits and did not inhibit the activation of PLC-β3 by Gβ ₁ γ ₂ In contrast, the peptide robustly prevented activation of PLC-β3 or p63RhoGEF by Gα _q ; it also prevented G protein-coupled receptor-promoted neuronal depolarization downstream of Gα _q in the mouse prefrontal cortex. Moreover, a genetically encoded form of this peptide flanked by fluorescent proteins inhibited Gα _q -dependent activation of PLC-β3 at least as effectively as a dominant-negative form of full-length PLC-β3. These attributes suggest that related, cell-penetrating peptides should effectively inhibit active Gα _q in cells and that these and genetically encoded sequences may find application as molecular probes, drug leads, and biosensors to monitor the spatiotemporal activation of Gα _q in cells.
(© 2016 by The American Society for Biochemistry and Molecular Biology, Inc.)