Figure 1.

Three types of autophagy and cellular and molecular events in an autophagic pathway. (A) There are three types of autophagy. In macroautophagy, which is the main route of cellular degradation, an autophagosome (a double-layered membrane vesicle) is formed, which fuses with lysosomes to degrade the cellular constituents or pathogens. Microautophagy is characterized by the removal of cellular constituents via the budding of an autophagic body at the lysosomal membrane. In chaperone-mediated autophagy, a signaling motif that contains molecules is transported with the chaperone HSC70 via the LAMP-2A protein into lysosomes. (B) The autophagic pathway consists of three distinct stages. For process initiation, nucleation of the autophagic vesicle is needed. Atg6 (Beclin-1) and type III PI3-kinase are required for the initiation of isolation-membrane formation. Elongation and closure of the autophagosome membrane are regulated by two ubiquitin-like conjugation systems: LC3 and Atg12 conjugation systems. The autophagosome fuses with lysosomes and subsequently matures into an autolysosome to degrade the materials present inside the cell.