Pertussis-toxin-sensitive Gα subunits selectively bind to C-terminal domain of neuronal GIRK channels: evidence for a heterotrimeric G-protein-channel complex

Neuronal G-protein-gated inwardly rectifying potassium (Kir3; GIRK) channels are activated by G-protein-coupled receptors that selectively interact with PTX-sensitive (Gαi/o) G proteins. Although the Gβγ dimer is known to activate GIRK channels, the role of the Gαi/o subunit remains unclear. Here, we established that Gαo subunits co-immunoprecipitate with neuronal GIRK channels. In vitro binding studies led to the identification of six amino acids in the GIRK2 C-terminal domain essential for Gαo binding. Further studies suggested that the Gαi/oβγ heterotrimer binds to the GIRK2 C-terminal domain via Gα and not Gβγ. Gαi/o binding-impaired GIRK2 channels exhibited reduced receptor-activated currents, but retained normal ethanol- and Gβγ-activated currents. Finally, PTX-insensitive Gαq or Gαs subunits did not bind to the GIRK2 C-terminus. Together, these results suggest that the interaction of PTX-sensitive Gαi/o subunit with the GIRK2 C-terminal domain regulates G-protein receptor coupling, and may be important for establishing specific Gαi/o signaling pathways.