Autophagy Process

The next step of the process is formation of the sequestered vesicle. This is the main site that assembles and organizes the autophagy machinery.

Once sequestered the intracellular membranes form a cup-shaped structure around the cargo. The intermediate structure is termed a phagophore, or isolation membrane.

Vesicle expansion and completion

The membrane expands to completely enclose the cargo. Several important proteins play a role in this step. This step gives rise to the autophagosomes.

Retrieval

In this step the proteins that were involved in the previous steps must dissociate from the autophagosome. This is particularly problematic for integral membrane proteins like Atg9 that cannot separate from the vesicle. Most of the other proteins may be reused.

Targeting, docking and fusion of the vesicle with the lysosome/vacuole

The next step is to prevent the fusion of the incomplete Cvt vesicle or autophagosome with the lysosome or vacuole. This is done by special coat proteins present on their surfaces.

Once the vesicle is complete, it goes on to fuse with the degradative organelle. This forms an endosome.

Breakdown of the vesicle and its contents

The final step is breakdown of the vesicle and release of its cargo. The outer membrane of the sequestering vesicle breaks to become continuous with the membrane of the lysosome/vacuole.

This membrane is then removed through a microautophagic process. Opening of the vesicle by breaking down of the membrane releases the contents of the lumen.