Molecular basis of canonical and bactericidal autophagy.

Autophagy is a catabolic process by which cells degrade their own cytoplasmic constituents. Cells respond to the stress response of nutrient deficiency by degrading a portion of their cellular components to produce amino acids and energy. Recently, it became evident that the autophagic machinery is also involved in a kind of innate immune system. Some bacteria that invade mammalian cells are eventually entrapped in an autophagic membrane structure. In this review, we describe the current understanding of three of the basic components of the canonical autophagy machinery-LC3, the Atg16L complex and phosphatidylinositol 3-phosphate (PI3P)-which are dynamically associated with the autophagic structure. LC3 is proposed to function in autophagosome closure, whereas the Atg16L complex functions as an E3-like protein in ubiquitination-like reactions in the LC3 lipidation system. PI3P is a key determinant of the autophagic membrane. Further, their relation to bactericidal autophagy (i.e. xenophagy) will be introduced.