The Cytoplasm: Lysosomes and Lysosomal Disorders

Abstract

Lysosomes are enriched in hydrolytic enzymes working at low pH, which include proteases, lipases, glycosidases, nucleases, phosphatases, and sulfatases, and are responsible for elimination of “unwanted” molecules derived from both the cell itself (autophagy, cf. Fig. 74) or from outside of the cells (heterophagy). However, contrary to the historic view of the lysosome as a terminal degradation compartment and as a unit used in the cells mainly as a disposal for garbage, it is increasingly becoming clear that lysosomes are dynamic organelles that receive continuous input from three sides, via the biosynthetic, endocytic, and autophagic pathways. Today, lysosomes cannot be seen as terminal or dead-end compartments. They are able to fuse with late endosomes involving “kiss-and-run”-mechanisms and are also capable of fusing with the plasma membrane.