Identification of Critical Residues Controlling G Protein-gated Inwardly Rectifying K+Channel Activity through Interactions with the βγ Subunits of G Proteins*

G protein-sensitive inwardly rectifying potassium (GIRK) channels are activated through direct interactions of their cytoplasmic N- and C-terminal domains with the βγ subunits of G proteins. By using a combination of biochemical and electrophysiological approaches, we identified minimal N- and C-terminal Gβγ-binding domains responsible for stimulation of GIRK4 channel activity. Within these domains one N-terminal residue, His-64, and one C-terminal residue, Leu-268, proved critical for Gβγ-mediated GIRK4 activity. Moreover, mutations at these GIRK4 sites reduced significantly binding of the channel domains to Gβγ. The corresponding residues in GIRK1 also showed a critical involvement in Gβγ sensitivity. In GIRK4/GIRK1 heteromers the GIRK4 His-64 and Leu-268 residues showed greater contributions to Gβγ sensitivity than did the corresponding GIRK1 His-57 and Leu-262 residues. These results identify functionally important channel interaction sites with the βγ subunits of G proteins, critical for channel activity.