Re-routing GPR56 signalling using Ga_12/13 G protein chimeras

Adhesion G protein-coupled receptors (aGPCRs) constitute the second largest subclass of the GPCR superfamily. Although canonical GPCRs are explored pharmacologically as drug targets, no clinically approved drugs target the aGPCR family so far. The aGPCR GPR56/ADGRG1 stands out as an especially promising target, given its direct link to the monogenetic disease bilateral frontoparietal polymicrogyria and implications in cancers. Key to understanding GPCR pharmacology has been mapping out intracellular signalling activity. Detection of GPCR signalling in the Ga-s/Ga-i/Ga-q G protein pathways is feasible with second messenger detection systems. However, in the case of Ga-12/13-coupled receptors, like GPR56, signalling detection is more challenging due to the lack of direct second messenger generation. To overcome this challenge, we engineered a Ga-q chimera to translate Ga-12/13 signalling. We show the ability of the chimeric Ga(?6q12myr )and Ga-?6q13myr to translate basal Ga-12/13 signalling of GPR56 to a Ga(q )readout in transcription factor luciferase reporter systems and show that the established peptide ligands (P7 and P19) function to enhance this signal. We further demonstrate the ability to directly influence the generation of second messengers in inositol-3-phosphate assays. In the future, these chimeric G proteins could facilitate basic functional studies, drug screenings and deorphanization of other aGPCRs.