G-protein-coupled receptors (GPCRs) are seven-transmembrane helix proteins that are involved in a number of sensory functions from vision to blood pressure regulation. GPR68 is a GPCR that is activated by extracellular protons and acts as a bona fide shear sensor that is important for vascular physiology. Moreover, GPR68 is upregulated in many cancers, but an optical sensor that would facilitate its study beyond the vasculature has been lacking thus far. Now, Jérôme Lacroix and colleagues (Ozkan et al., 2021) engineer a genetically encoded fluorescent reporter for GPR68 by translocating a circularly permuted green fluorescent protein module into the third intracellular loop of human GPR68, and name the tool iGlow. To demonstrate its usefulness, the authors show that iGlow responds to the known endogenous activators of GPR68, fluid shear stress and extracellular acidification. Validating the specificity of the biosensor, they report that iGlow responds to the synthetic GPR68-selective agonist Ogerin, but not to a non-active Ogerin analogue. Furthermore, iGlow is shown to be insensitive to pharmacological modulation of G-protein signalling, disruption of the actin cytoskeleton and incubation with a toxin that is thought to inhibit certain mechanosensitive ion channels. Therefore, this tool opens the door to unlocking new biological roles for GPR68.
