High-resolution structures of inwardly rectifying K+ channels have also enabled visualization of amino acids implicated in PIP2 binding as well as possible gating mechanisms for ethanol and Na+ modulation. Clusters of basic (positively charged) amino acids of the cytoplasmic domain58-60 are positioned in close proximity to the plasma membrane, where they are poised to interact directly with negatively changed membrane phospholipids and couple with the two gates (M2 and G loop) (Figure 2A). Recently, a hydrophobic pocket formed by the N-terminal domain, and the C-terminal βD-βE and βL-βM sheets has been identified as a site for ethanol activation of GIRK channels46. Bulky amino acid substitutions of a Leu located in the βD-βE sheet of the hydrophobic pocket decreases ethanol-dependent activation46 (Figure 2B). A structural analysis of GIRK2 has also provided a possible mechanism for Na+ dependent regulation of GIRK channels: Na+ may promote PIP2 binding to GIRK channels by breaking a hydrogen bond formed between an aspartate in the βC-βD sheet and an arginine66,91. These high-resolution protein structures have provided important snapshots of inward rectifiers in different conformational states as
