ATG conjugation-dependent degradation of the inner autophagosomal membrane is a key step for autophagosome maturation.

Although the autophagy-related (ATG) conjugation systems are thought to be important for a late step of autophagosome formation, their precise function has been poorly understood because they are also required for localization of the most important autophagosomal marker LC3. In our recent study we found that, using the autophagosomal SNARE STX17 (syntaxin 17) as an alternative marker, autophagosome-like structures were generated in ATG conjugation system-deficient cells. Those structures could fuse with lysosomes but the degradation of the inner autophagosomal membrane was significantly delayed. We suggest that the ATG conjugation-dependent closure of autophagosomes causes the inner autophagosomal membrane to become sensitive to lysosomal degradation.