Purification and characterization of a ubiquitin-like system for autophagosome formation.

Autophagy refers to the bulk degradation of cellular proteins and organelles through an autophagosome and plays a pivotal role in the development, cellular differentiation, aging, and elimination of aberrant structures. A failure of autophagy has been implicated in a growing list of mammalian disease states, including cancer and cardiomyopathy. Two ubiquitin-like systems are highly involved in autophagy, especially in the formation of autophagosomes. Here, we purified and characterized Atg7 (an E1-like enzyme), and Atg3 and Atg10 (E2-like enzymes) in order to gain an insight into the role played by ubiquitin-like systems in the formation of autophagosomes. Interestingly, we observed that Atg7 forms a homodimer to construct an active conformation, unlike other E1-like enzymes. Although Atg3 was detected as a monomer under physiological conditions, Atg10 existed in an oligomeric form, indicating that the mechanism by which Atg10 functions may differ from that of Atg3.