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 (G(alphai/o)) G proteins. Although the G(betagamma) dimer is known to activate GIRK channels, the role of the G(alphai/o) subunit remains unclear. Here, we established that G(alphao) 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 G(alphao) binding. Further studies suggested that the G(alphai/obetagamma) heterotrimer hinds to the GIRK2 C-terminal domain via G(alpha) and not G(betagamma)(.) G(alphai/o) binding-impaired GIRK2 channels exhibited reduced receptor-activated currents, but retained normal ethanol- and G(betagamma)-activated currents. Finally, PTX-insensitive G(alphaq) or G(alphas) subunits did not bind to the GIRK2 C-terminus. Together, these results suggest that the interaction of PTX-sensitive G(alphai/o) subunit with the GIRK2 C-terminal domain regulates G-protein receptor coupling, and may be important for establishing specific G(alphai/o) signaling pathways. (C) 2004 Elsevier Inc. All rights reserved.