Structural basis of Atg8 activation by a homodimeric E1, Atg7.

E1 enzymes activate ubiquitin-like proteins and transfer them to cognate E2 enzymes. Atg7, a noncanonical E1, activates two ubiquitin-like proteins, Atg8 and Atg12, and plays a crucial role in autophagy. Here, we report crystal structures of full-length Atg7 and its C-terminal domain bound to Atg8 and MgATP, as well as a solution structure of Atg8 bound to the extreme C-terminal domain (ECTD) of Atg7. The unique N-terminal domain (NTD) of Atg7 is responsible for Atg3 (E2) binding, whereas its C-terminal domain is comprised of a homodimeric adenylation domain (AD) and ECTD. The structural and biochemical data demonstrate that Atg8 is initially recognized by the C-terminal tail of ECTD and is then transferred to an AD, where the Atg8 C terminus is attacked by the catalytic cysteine to form a thioester bond. Atg8 is then transferred via a trans mechanism to the Atg3 bound to the NTD of the opposite protomer within a dimer.

Noda NN ，Satoo K ，Fujioka Y ，Kumeta H ，Ogura K ，Nakatogawa H ，Ohsumi Y ，Inagaki F ... -  《-》

Atg8 transfer from Atg7 to Atg3: a distinctive E1-E2 architecture and mechanism in the autophagy pathway.

Taherbhoy AM ，Tait SW ，Kaiser SE ，Williams AH ，Deng A ，Nourse A ，Hammel M ，Kurinov I ，Rock CO ，Green DR ，Schulman BA ... -  《-》

Insights into noncanonical E1 enzyme activation from the structure of autophagic E1 Atg7 with Atg8.

Hong SB ，Kim BW ，Lee KE ，Kim SW ，Jeon H ，Kim J ，Song HK ... -  《-》

Atg7 Activates an Autophagy-Essential Ubiquitin-like Protein Atg8 through Multi-Step Recognition.

Atg8 is a unique ubiquitin-like protein that is covalently conjugated with a phosphatidylethanolamine through reactions similar to ubiquitination and plays essential roles in autophagy. Atg7 is the E1 enzyme for Atg8, and it activates the C-terminal Gly116 of Atg8 using ATP. Here, we report the crystal structure of Atg8 bound to the C-terminal domain of Atg7 in an unprecedented mode. Atg8 neither contacts with the central β-sheet nor binds to the catalytic site of Atg7, both of which were observed in previously reported Atg7-Atg8 structures. Instead, Atg8 binds to the C-terminal α-helix and crossover loop, thereby changing the autoinhibited conformation of the crossover loop observed in the free Atg7 structure into a short helix and a disordered loop. Mutational analyses suggested that this interaction mode is important for the activation reaction. We propose that Atg7 recognizes Atg8 through multiple steps, which would be necessary to induce a conformational change in Atg7 that is optimal for the activation reaction.

Yamaguchi M ，Satoo K ，Suzuki H ，Fujioka Y ，Ohsumi Y ，Inagaki F ，Noda NN ... -  《-》

The crystal structure of Atg3, an autophagy-related ubiquitin carrier protein (E2) enzyme that mediates Atg8 lipidation.

Yamada Y ，Suzuki NN ，Hanada T ，Ichimura Y ，Kumeta H ，Fujioka Y ，Ohsumi Y ，Inagaki F ... -  《JOURNAL OF BIOLOGICAL CHEMISTRY》