The G protein-gated inwardly rectifying K+ (GIRK) channel was the first example of a protein whose function was shown to be regulated by direct interactions with the betagamma subunits of GTP-binding (G) proteins (Logothetis et al., 1987). In this FIRCA they proposed to identify the region(s) in Gbeta subunits that interact(s) with GIRK channels. While Gbeta1-beta4 can activate GIRK channels with similar efficiency, Gbeta5 fails to do so even though it shows intact expression. They will use a chimeric strategy between Gbeta1 and Gbeta5 to identify the region between the two isoforms that is responsible for the difference in their abilities to stimulate GIRK activity. As they have already narrowed the region down to 95 amino acids, they will further narrow down this region utilizing a similar chimeric approach, so that through site-directed mutagenesis they can identify the specific amino acid residues responsible for the functional differences between the two beta subunits. Using a deletion mutagenesis approach they will attempt to identify the minimal Gbeta regions capable of binding the channel. Design of Gbeta peptides capable of affecting channel activity will follow identification of the minimal Gbeta regions.
