Use of Caenorhabditis elegans Gαq chimeras to detect G-protein-coupled receptor signals

G-protein-coupled receptors (GPCRs) activate heterotrimeric G-proteins (G(i)-, G(s)-, G(q)-, or G(12)-like) to generate specific intracellular responses, depending on the receptor/G-protein coupling. The aim was to enable a majority of GPCRs to generate a predetermined output by signaling through a single G-protein-supported pathway. The authors focused on calcium responses as the output, then engineered G alpha(q) to promote promiscuous receptor interactions. Starting with a human G alpha(q) containing 5 G alpha(z) residues in the C-tertninal receptor recognition domain (hG alpha(q/z5)) they evaluated agonist-stimulated calcium responses for 33 diverse GPCRs (G(i)-, G(s)-, and G(q)-coupled) and found 20 of 33 responders. In parallel, they tested Caenorhabditis elegans G alpha(q) containing 5 or 9 C-terminal G alpha(z) residues (cG alpha(q/z5), cG alpha(q/z9)). Signal detection was enhanced with cG alpha(q/z5) and cG alpha(q/z9) (yielding 25/33 and 26/33 responders, respectively). In a separate study of G alpha(s)-coupled receptors, the authors compared hG alpha(q/s5) versus hG alpha(q/s9), cG alpha(q/s9), and cG alpha(q/s21) and observed optimal function with cG alpha(q/s9). Cotransfection of an engineered G alpha(q) "cocktail" (cG alpha(q/z5) plus cG alpha(q/s9)) provided a powerful and efficient screening platform. When the chimeras included N-terminal myristoylation sites (to promote membrane localization), calcium responses were sustained or improved, depending on the receptor. This approach toward a "universal functional assay" is particularly useful for orphan GPCRs whose signaling pathways are unknown.