Coupling Gβγ-dependent activation to channel opening via pore elements in inwardly rectifying potassium channels

G protein-coupled inwardly rectifying potassium channels, GIRK/Kir3.x, are gated by the G beta gamma subunits of the G protein. The molecular mechanism of gating was investigated by employing a novel yeast-based random mutagenesis approach that selected for channel mutants that are active in the absence of G beta gamma. Mutations in TM2 were found that mimicked the G beta gamma -activated state. The activity of these channel mutants was independent of receptor stimulation and of the availability of heterologously expressed G beta gamma subunits but depended on PtdIns(4,5)P-2. The results suggest that the TM2 region plays a key role in channel gating following G beta gamma binding in a phospholipid-dependent manner. This mechanism of gating in inwardly rectifying K+ channels may be similar to the involvement of the homologous region in prokaryotic KcsA potassium channel and, thus, suggests evolutionary conservation of the gating structure.