Targeting G protein-coupled receptor signaling at the G protein level with a selective nanobody inhibitor

G protein-coupled receptors (GPCRs) activate heterotrimeric G proteins by mediating a GDP to GTP exchange in the Ga subunit. This leads to dissociation of the heterotrimer into GaGTP and G beta gamma dimer. The Ga-GTP and G beta gamma dimer each regulate a variety of downstream pathways to control various aspects of human physiology. Dysregulated G beta gamma-signaling is a central element of various neurological and cancer-related anomalies. However, G beta gamma also serves as a negative regulator of Ga that is essential for G protein inactivation, and thus has the potential for numerous side effects when targeted therapeutically. Here we report a llama-derived nanobody (Nb5) that binds tightly to the G beta gamma dimer. Nb5 responds to all combinations of beta-subtypes and.-subtypes and competes with other G beta gamma-regulatory proteins for a common binding site on the G beta gamma dimer. Despite its inhibitory effect on G beta gamma-mediated signaling, Nb5 has no effect on G alpha(q)-mediated and G alpha(s)-mediated signaling events in living cells.