Specificity of intracellular termini interactions of G protein-gated inwardly rectifying potassium channels

Ion channels and pumps help in maintaining different ion gradients across this membrane, thereby creating a membrane potential. One class of potassium channels, called inward rectifiers (Kir) are unique due to their ability to allow a greater influx than efflux of K+ ions. The G-protein activated inwardly rectifying potassium channel (GIRK) is the only known Kir channel that is activated by the direct binding of Gβγ. GIRK channels play important physiological roles in neurons, myocytes, pancreatic cells and other cell types, where they restore and maintain the resting membrane potential of the cell and link G protein signaling to changes in potential. Abnormalities in these channels are related to many disease states and knowledge of the mechanism of gating and activation of these channels can be useful in developing possible pharmaceutical therapy for the disease states. Many studies have been conducted to understand the mechanism of interactions between different regions of the channel that translate to function. Our study focuses on the cytoplasmic N- and C-termini of GIRK1/GIRK4 heteromeric channels. Previous studies (Sarac et al., 2005) have demonstrated the importance of specific residues in a hydrophobic pocket formed between interacting intracellular domain within a subunit and between subunits. We have further investigated the nature of the interactions between residues in this pocket. Mutational analyses reveal that intra-termini associations are not disrupted by complementary mutations of I331 and F46 in the C- and N-termini, respectively of GIRK1 subunits. Interactions between termini of alternative subunits are not affected by mutation of the GIRK4 N-terminal residue, Y53 to either its complementary residue or a polar amino acid. Together, these results suggest that maintaining the structural integrity and hydrophobicity of the pocket formed by the N- and C-termini is important for termini interactions and channel function.