Which inhibitor blocks autophagosome-lysosome fusion?
Autophagic flux progresses through initiation, elongation, closure, fusion and degradation. Efficient cargo clearance requires autophagosome lysosome fusion mediated by small GTPase RAB7, HOPS complex and SNARE proteins STX17 SNAP29 VAMP8 and YKT6, plus tethering factors like PLEKHM1. Bafilomycin A1, a macrolide isolated from Streptomyces griseus, is a high affinity inhibitor of vacuolar type H+ ATPase V0 domain c subunit, blocking proton pumping into lysosome lumen. Collapse of acidic pH inactivates cathepsins and prevents LysoTracker accumulation. Recent work shows additional target ER calcium ATPase SERCA, whose inhibition perturbs local calcium transients required for SNARE mediated membrane merger. Consequently autophagosomes marked by lipidated LC3-II and adaptor p62 SQSTM1 accumulate as non degradative vesicles, flux is stalled, and cells display enlarged autophagosomes by electron microscopy. Brefeldin A inhibits GBF1 ARF1 dependent Golgi transport, tunicamycin blocks N linked glycosylation, colchicine depolymerizes microtubules, none specifically block this final fusion step. Bafilomycin therefore serves as classic autophagy flux inhibitor in research and validation assays.
Ref: NCBI Bookshelf, Molecular Biology of the Cell, Section: Autophagosome-Lysosome Fusion and V-ATPase Inhibitors.