Taking out the trash

Cell 181, 1176–1187 (2020)

Mitophagy uses lysosomal degradation to remove defective mitochondria. Although probes to detect and measure mitophagy such as mt-mKeima have been developed, they can only image live specimens due to their reliance on a pH difference inside and outside the lysosome. To develop an improved mitophagy probe, Katayama et al. screened a library of fluorescent proteins and identified a cyan-emitting protein called TOLLES that is resistant to lysosomal environments. They used TOLLES as a FRET donor and a YFP variant (YPet) as a FRET acceptor to develop a ratiometric autophagy indicator called SRAI. Starvation of cells to induce autophagy resulted in movement of SRAI to the lysosome, where YPet is degraded, producing a high TOLLES/YPet ratio that was also retained in fixed samples. A mitochondrially targeted variant, mito-SRAI, could detect mitophagy induced by the uncoupler FCCP and Parkin expression and enabled the identification of a compound that enhances mitophagy on damaged mitochondria while sparing intact mitochondria. Overall, the development of mito-SRAI as a reliable readout of mitophagy offers the potential for further understanding of how defects in mitophagy can result in diseases.

Credit: Koji Nagasawa and Yoshiyuki Tsujihata

Author information



Corresponding author

Correspondence to Grant Miura.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Miura, G. Taking out the trash. Nat Chem Biol 16, 712 (2020).

Download citation