During a process of autophagy, a spherical double-membrane structure, termed autophagosome, is formed within a cell. A number of autophagy-related (ATGs) proteins, together with other proteins, are involved in the process to form autophagosomes: starting from the formation of the autophagy initiation complex to elongating autophagosome membranes. After elongation, the membrane closes and autophagosome formation is completed.
Autophagy-related proteins play a crutial role in autophagy signaling transduction. About 40 autophagy-related genes have been identified as necessary for various types of autophagy so far. And the 15 core genes encoding autophagy-related proteins in yeast (ATG1–ATG10, ATG12–ATG14, ATG16 and ATG18) are conserved in mammals, which indicates that autophagy is an evolutionarily conserved process.
As in yeast, mammalian core autophagy-related proteins can be classified into several functional units: the ULK complex, ATG9L, the class III PI(3)K (phosphatidylinositol-3-OH kinase) complex, the ATG2-WIPI complex, the ATG12 conjugation system, and the LC3 conjugation system. It has been reported that autophagy-related proteins are associated with human autoimmune disorders, cancer, and various infectious diseases.
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