Fluorescence ratiometric detection of ligand-induced receptor internalization using extracellular coiled-coil tag-probe labeling

► We have developed a new method for labeling receptors using coiled-coil formation. ► The β2 adrenoceptors were doubly labeled with pH-sensitive and insensitive dyes. ► Acidification in endosomes is a useful indicator of membrane receptor activity. ► Agonist-induced endocytosis of the receptors changed fluorescence intensity ratio. ► The concentration-dependent response demonstrates accurate detection of the activity.