Autolysosome

An autolysosome is the degradative compartment formed during macroautophagy when an autophagosome fuses with a lysosome. The resulting organelle contains lysosomal hydrolases and an acidic interior, creating the environment where autophagic cargo is broken down.

Formation and composition: Autophagosomes, which sequester cytoplasmic material such as damaged organelles, protein aggregates, or invasive pathogens, are delivered to lysosomes. Membrane fusion is mediated by tethering factors, Rab GTPases, and SNARE proteins, resulting in the autolysosome. The interior becomes highly acidic, activating lysosomal enzymes.

Function and cargo: Within the autolysosome, proteases, lipases, nucleases, and glycosidases degrade the cargo into basic building blocks—amino acids, fatty acids, sugars, and nucleotides. These products are transported back into the cytosol for reuse, supporting cellular maintenance during nutrient stress and remodeling. Selective autophagy routes, such as mitophagy or aggrephagy, direct specific targets to autolysosomes for degradation.

Regulation and significance: Autolysosome performance is a key aspect of autophagic flux and lysosome biogenesis. Proper function supports cellular homeostasis, energy balance, and innate defense. Defects in autolysosome formation or enzyme activity are associated with lysosomal storage disorders, neurodegenerative diseases, and aging-related decline.

Additional notes: Following cargo digestion, the lysosome components are replenished and, in many cases, reformed into functional lysosomes to sustain ongoing degradative capacity. The autolysosome is a central component of the lysosome-autophagosome axis that maintains cellular quality control.