lysosomeendosome

Lysosomeendosome is not a formal organelle, but a way to describe the close functional relationship between endosomes and lysosomes in the cell’s degradative and trafficking pathways. Endosomes originate from the plasma membrane through endocytosis and act as sorting stations for internalized material. They progress from early endosomes, which decide whether cargo is recycled or sent onward, to late endosomes, which acquire more degradative capacity and prepare cargo for lysosomal destruction. Lysosomes are membrane-bound organelles with an acidic interior holding a broad set of hydrolytic enzymes that dismantle proteins, lipids, nucleic acids, and carbohydrates. The endosome–lysosome axis thus coordinates cargo routing, receptor downregulation, nutrient signaling, and antigen processing.

Maturation and fusion along this axis are tightly controlled. Early endosomes marked by Rab5 mature into late endosomes marked by Rab7, and eventually fuse with lysosomes to deliver degrader enzymes and substrates for breakdown. The process is orchestrated by tethering and fusion machinery, including SNARE proteins and the HOPS complex, as well as Rab GTPases that coordinate organelle identity. The ESCRT machinery also participates in sorting ubiquitinated membrane proteins into intralumenal vesicles within endosomes, earmarking them for lysosomal degradation. Lysosomes themselves can be renewed through autophagy, where autophagosomes fuse with lysosomes to recycle intracellular components.

Disruptions in endosome–lysosome trafficking or function are linked to a range of diseases, including lysosomal storage disorders, neurodegenerative diseases, and immune dysfunction. Understanding the lysosomeendosome interface is essential for grasping how cells regulate degradation, nutrient sensing, and membrane protein turnover.