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. Author manuscript; available in PMC: 2009 Dec 1.
Published in final edited form as: Biochim Biophys Acta. 2008 Oct 10;1782(12):691–699. doi: 10.1016/j.bbadis.2008.10.002

Figure 2.

Figure 2

Assembly and elongation of autophagic membranes are accomplished via sequential action of UPS-like E1-E2-E3 cascades. In each case, an E1 enzyme activates a ubiquitin-like protein (UBL) such as ubiquitin, Atg12, or Atg8. The UBL is then transferred to an E2 conjugating enzyme, followed by an association with an E3 ligase that promotes association of the UBL and its target. (a) In the UPS, ubiquitination of substrates is accomplished by an E1-activating enzyme, E2-conjugating enzyme, and an E3-ligase. (b) In the first arm of the Atg conjugation pathway, Atg12 associates with the E1-like Atg7, is transferred to the E2-like Atg10, and is subsequently conjugated to Atg5. No E3-like protein has been identified in this pathway. (c) In the second arm of the Atg conjugation pathway, Atg8 associates with the E1-like Atg7, is transferred to the E2-like Atg3, and is conjugated to PE via the E3-like action of the Atg12-Atg5 complex. Adapted from [101] with permission.