Development of a genetically encoded fluorescent indicator for facilitating deorphanization of GPR52

GPR52 is an orphan G protein-coupled receptor implicated in psychiatric and neurodegenerative disorders, but its endogenous ligand remains unidentified, limiting the exploration of its physiological functions and therapeutic potential. We pioneered a novel methodology for orphan GPCR ligand discovery utilizing the GPCR-activation-based (GRAB) strategy by developing GPR52-1.0, a genetically encoded fluorescent sensor. GPR52-1.0 exhibits excellent membrane trafficking and high sensitivity in HEK293T cells, cultured neurons, and acute mouse brain slices. Notably, it detects neuronal activity–dependent endogenous ligand release in the striatum, with responses abolished by a specific antagonist. This sensor provides a powerful tool for identifying GPR52’s endogenous ligand(s) and enables real-time monitoring of its activation. Our work lays the foundation for uncovering GPR52’s physiological roles and supports future efforts to develop GPR52-targeted therapeutics.