FIGURE 3.

The GPCR biosensors utilizing cpFP and nanobody. (A) Schematic design of the ligand-sensing biosensors based on cpFP (Marvin et al., 2013). The fluorescent signal of cpFP inserted in the ligand-sensing domain is increased upon ligand binding. (B) Schematic design of fluorescent biosensors detecting the conformational change of GPCRs (Patriarchi et al., 2018; Sun et al., 2018). In the left panel, the fluorescent signal of the cpFP inserted in the ICL3 region of the GPCR is increased upon the conformational change of the GPCR. In the right panel, the YFP-tagged nanobody can specifically bind to the GPCR of active conformation. As a luciferase is fused to the GPCR, thus the BRET signal between the YFP and the luciferase is increased. (C) Schematic design of the cpFP- and nanobody-based biosensors detecting the recruitment of G proteins (Hoare et al., 2020). (D) Different color variants of cpFP-based GPCR biosensors (Patriarchi et al., 2020; Sun et al., 2020; Labouesse and Patriarchi, 2021).