Autofagosoom

Autofagosoom, commonly referred to in English as autophagosome, is a double-membrane vesicle that forms during autophagy to sequester cytoplasmic material for degradation in lysosomes. The structure is central to cellular quality control, capturing damaged organelles, misfolded proteins, and other cytoplasmic components for recycling. The term autofagosoom is used in some languages to describe this same organelle.

Formation begins with initiation of a phagophore, a cup-shaped membrane that expands to enclose cargo. This process is regulated by conserved autophagy-related (ATG) proteins. Under nutrient stress or cellular damage, the ULK1 kinase complex initiates phagophore formation, followed by activation of a class III PI3K complex (including Beclin-1) that generates phosphatidylinositol 3-phosphate to recruit additional autophagy factors. The membrane elongates with the help of the Atg5–Atg12–Atg16L1 complex and the lipidation of LC3 (Atg8) to phosphatidylethanolamine, producing LC3-II on the growing membrane and facilitating cargo capture via receptors such as p62/SQSTM1 that bind ubiquitinated cargo and LC3.

Maturation involves closure of the autophagosome and its fusion with lysosomes, forming an autolysosome where hydrolases degrade the contents. This fusion is mediated by SNARE proteins and tethering factors, including the HOPS complex. The resulting macromolecules are recycled for reuse by the cell.

Autophagosomes contribute to cellular homeostasis, stress responses, and development. Dysregulation of autophagosome formation or function is associated with aging, neurodegenerative diseases, cancer, and infectious diseases, making autophagy a focus of biomedical research.