Fig. 5.

Proteins can be incorporated into lysosomes for degradation by different mechanisms. Macroautophagy (upper part) is the main lysosomal degradative route and involves the sequestration by a segregating structure of large areas of cytoplasm, typically including whole organelles, to make up autophagosomes. These pre-lysosomes fuse with endosomes and lysosomes to form autolysosomes that degrade its cytoplasmic content. In addition to macroautophagy, other mechanisms (lower part) have been described whereby lysosomes could also participate in intracellular protein degradation, including endocytosis, crinophagy, microautophagy and chaperone-mediated autophagy (for details, see text)