Figures & data
Figure 1 Knockdown of VAMP8 and Vti1b inhibits colocalization of xenophagosomes with lysosomes. HeLa cells expressing GFP-LC3 were transfected with control siRN A, and VAMP8 and Vti1b siRN As. Following infection with GAS, the cells were fixed and incubated with anti-LAMP1 antibodies and observed with a confocal microscope. Cellular and bacterial DN A were stained with DAPI. LAMP1 failed to colocalize with GFP-LC3 in the SNARE -depleted cells. Boxed regions in the upper panels show magnifications of the lower panels. Bars indicate 5 µm.
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.
