Figure 2.
SNARE proteins VAMP8 and Vti1b fuse xenophagosomes/canonical autophagosomes with lysosomes. Intracellular GAS organisms are entrapped within xenophagosomes, then xenophagosomes undergo a stepwise maturation process that consists of a fusion event with lysosomes, which allows the autophagic vacuole to acquire lysosomal proteases. That fusion is mediated by a combinational complex of VAMP8 and Vti1b from xenophagosomes. Finally, GAS organisms are degraded by xenophagosomes (autolysosomes) possessing lysosomal degradation enzymes. The complex of VAMP8 and Vti1b also mediates the fusion between canonical autophagosomes and lysosomes. Vti1b originates from autophagic vacuoles, whereas VAMP8 is recruited from lysosomes to autophagic compartments prior to fusion.