Mapping these G protein-interaction sites on the high-resolution structures provides clues to possible mechanisms of Gβγ gating (Figure 2A,B). For example, many of the regions implicated in Gβγ activation fall on the external side of the cytoplasmic domains, along an interface formed by two adjacent subunits (Figure 2B). Originating from different subunits, sequences from the N-terminal domain and the βD-βE and βL-βM sheets in the C-terminal domain contribute to this interface. An interaction between the N- and C-terminal domains of two subunits has been shown to be important for assembly and gating of GIRK channels 86. Recently, a hydrophobic pocket has been identified in this subunit interface and implicated in G protein-dependent activation of GIRK channels46. FRET (fluorescence resonance energy transfer, see Box 2) measurements further reveal that Gβγ activation elicits a structural change, possibly a rotation, in the GIRK N- and C-terminal domains87. Systematic mutagenesis studies have indicated that specific amino acids in the M2 transmembrane domain88-90 and G-loop65,67,68 form a barrier to ion conduction in the closed state; thus conformational changes triggered in the cytoplasmic domains must couple
