Fluorescent labeling of membrane proteins on the surface of living cells by a self-catalytic glutathione S-transferase omega 1 tag

Imaging a specific protein of interest in live cell has versatile applications in biological research. Recently, diverse chemical tags have been developed to overcome the limits of autofluorescence protein (FP) tags. However, current chemical methods still need to be progressed to compete with FPs in the scope of specificity and convenience in staining procedure. We report a novel protein tagging method that provides a convenient and specific fluorescent labeling of membrane proteins. Omega tag is developed by employing a mammalian enzyme glutathione sulfur-transferase omega 1 (GSTO1) and its partner dye, 5-bromomethyl fluorescein (BMF). Omega-tagged membrane proteins were labeled by BMF efficiently for live cell imaging and in-gel analysis. Endocytosis of epidermal growth factor receptor (EGFR) was successfully visualized by using this Omega tagging system. Omega tag will provide a convenient tool for the physiological study of membrane proteins in live cells.