Lysosome

A lysosome is a membrane-bound organelle found in nearly all animal cells. It contains a broad set of acid hydrolases that function optimally in an acidic interior, and it is surrounded by a single phospholipid membrane. The lysosome’s interior pH is typically around 4.5 to 5.0, maintained primarily by V-ATPase proton pumps.

Lysosomal enzymes are synthesized in the endoplasmic reticulum and tagged in the Golgi apparatus with mannose-6-phosphate, which directs their delivery to lysosomes via specific receptors. Once in the lysosome, these enzymes degrade proteins, nucleic acids, carbohydrates, and lipids obtained from endocytosis, phagocytosis, or autophagy. Degradation occurs in structures such as autolysosomes formed when autophagosomes fuse with lysosomes, or endolysosomes formed from endosomes.

Lysosomes also host membrane proteins such as LAMP1 and LAMP2 that stabilize the lysosomal membrane and participate in trafficking. In addition to digestion, lysosomes play a role in immune defense by breaking down microbial invaders. Some cells can secrete lysosomal contents through exocytosis.

Dysfunction of lysosomes leads to lysosomal storage diseases, caused by deficient hydrolases or trafficking defects. Examples include Tay-Sachs disease (HEXA deficiency), Gaucher disease (GBA deficiency), and Pompe disease (acid alpha-glucosidase deficiency), among others. These conditions result in accumulation of undegraded substrates within cells.

Research on lysosomes covers autophagy, lysosomal biogenesis regulated by transcription factors such as TFEB, and therapeutic approaches including enzyme replacement therapy and gene therapy.