Lysosomi

Lysosomi, known in English as lysosomes, are membrane-bound organelles found in most animal cells and in many plant and fungal cells. They contain a broad set of hydrolytic enzymes that function best in an acidic interior, enabling the breakdown of proteins, nucleic acids, carbohydrates, and lipids. The lumen of a lysosome maintains a pH of about 4.5 to 5.0, achieved in part by proton pumps in the membrane called v-ATPases.

Structure and trafficking

The lysosome is bounded by a single membrane that protects the rest of the cell from its potent enzymes. Lysosomal enzymes are synthesized in the endoplasmic reticulum and marked with mannose-6-phosphate tags in the Golgi apparatus, directing them to lysosomes via mannose-6-phosphate receptors. Lysosomal membrane proteins, such as LAMP1 and LAMP2, support membrane integrity and seal the internal environment. Lysosomes arise from late endosomes and can fuse with autophagosomes during autophagy, expanding the organelle’s repertoire of cargo.

Functions

Lysosomes participate in endocytosis, phagocytosis, and autophagy, degrading internalized material, worn-out organelles, and invading pathogens. The resulting macromolecular fragments are recycled to support cellular metabolism. They also participate in processes beyond degradation, including lipid turnover and nutrient sensing.

Clinical relevance

Impaired lysosome function leads to lysosomal storage disorders, caused by deficient enzymes or transport defects. Examples include Gaucher disease (glucocerebrosidase deficiency), Tay-Sachs disease (β-hexosaminidase A deficiency), and Pompe disease (acid α-glucosidase deficiency). Treatments include enzyme replacement therapy, substrate reduction therapy, pharmacological chaperones, and gene therapy. The discovery and study of lysosomes were led by Christian de Duve in the 1950s, earning him the Nobel Prize in Physiology or Medicine in 1974.