title: The structure of Atg4B-LC3 complex reveals the mechanism of LC3 processing and delipidation during autophagy.
abstract: Atg8 is conjugated to phosphatidylethanolamine (PE) by ubiquitin-like conjugation reactions. Atg8 has at least two functions in autophagy: membrane biogenesis and target recognition. Regulation of PE conjugation and deconjugation of Atg8 is crucial for these functions in which Atg4 has a critical function by both processing Atg8 precursors and deconjugating Atg8-PE. Here, we report the crystal structures of catalytically inert human Atg4B (HsAtg4B) in complex with processed and unprocessed forms of LC3, a mammalian orthologue of yeast Atg8. On LC3 binding, the regulatory loop and the N-terminal tail of HsAtg4B undergo large conformational changes. The regulatory loop masking the entrance of the active site of free HsAtg4B is lifted by LC3 Phe119, so that a groove is formed along which the LC3 tail enters the active site. At the same time, the N-terminal tail masking the exit of the active site of HsAtg4B in the free form is detached from the enzyme core and a large flat surface is exposed, which might enable the enzyme to access the membrane-bound LC3-PE.
authors.affiliation: Department of Structural Biology, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Satoo
authors.forename: Nobuo N
authors.initials: NN
authors.lastname: Noda
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kumeta
authors.forename: Yuko
authors.initials: Y
authors.lastname: Fujioka
authors.forename: Noboru
authors.initials: N
authors.lastname: Mizushima
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Ohsumi
authors.forename: Fuyuhiko
authors.initials: F
authors.lastname: Inagaki