A GTP-state specific cyclic peptide inhibitor of the GTPase Gαs

Abstract

The G protein-coupled receptor (GPCR) cascade leading to production of the second messenger cAMP is replete with pharmacologically targetable receptors and enzymes with the exception of the G subunit, Gs. GTPases remain largely undruggable given the difficulty of displacing high-affinity guanine nucleotides and the lack of other drug binding sites. We explored a chemical library of 1012 cyclic peptides in order to expand the chemical search for inhibitors of this enzyme class. We identified two macrocyclic peptides, GN13 and GD20, that antagonize the active and inactive states of Gs, respectively. Both macrocyclic peptides fine-tune Gs activity with high nucleotide-binding-state selectivity and G protein class-specificity. Co-crystal structures reveal that GN13 and GD20 distinguish the conformational differences within the switch II/3 pocket and block effector interactions. The Gs inhibitors showed strong activity in cellular contexts through binding to crystallographically defined pockets. The discovery of cyclic peptide inhibitors targeting Gs provides a path for further development of state-dependent GTPase inhibitors.