FIGURE 4.

Monitoring endosomal trafficking and degradation process of GPCRs with the GPCR-pH sensor. To confirm that GPCRs encounter the more acidic environment during the endosomal trafficking and degradation process (Marchese et al., 2008; Kim et al., 2021a), a GPCR-pH sensor is designed, which is composed of β2AR, a pH-sensitive FP (Bizzarri et al., 2009; Shen et al., 2014) and a pH-stable reference FP, which can confirm that GPCRs encounter acidic environment during endosomal trafficking pathways. Acidification in the endosomes and lysosomes decreases the fluorescent intensity of the pH-sensitive RFP, but not the reference FP, thus the acidic state of GPCRs can be predicted by the intensity ratios of pH sensitive-FP (red) and reference FP (green).