Monitoring Autophagy with Atg4B Protease‐Activated Aggregation‐Induced Emission Probe

Abstract Autophagy is crucial in the physical development and pathogenesis of disease. Monitoring autophagy is still limited by no real‐time and poor specificity. Herein, the authors report studies of Atg4B enzyme as a biomarker for autophagy and the development of an Atg4B‐responsive aggregation‐induced emission (AIE) probe, termed QM‐GFTN. Particularly, the incorporated peptide unit of GFTN endows good dispersion, but the state can be reversed when the hydrophilic peptide is cleaved by the Atg4B, thus realizing a light‐up fluorescence with high signal/noise ( S / N ) ratio. The probe exhibits excellent selectivity to Atg4B, and can respond to its activity in solution and living cells, thus efficiently distinguishing autophagy‐active from autophagy‐inactive states, greatly shortening the detection time comparing to the traditional methods. The fluorescence imaging of cells and autophagy‐inhibitor studies indicate that QM‐GFTN is specifically cleaved by Atg4B, and rules out the possibility of its self‐aggregation. By grafting Atg4B‐cleavable peptide to AIE fluorophore, the peptide‐based probe can carry out real‐time visualization of Atg4B activity with guaranteeing high specificity, serving as a great breakthrough to the detection of autophagy process in various autophagic cells, animal tissues, and even human pathological tissues.