title: The Atg12-Atg5 conjugate has a novel E3-like activity for protein lipidation in autophagy.
abstract: Autophagy is a bulk degradation process in eukaryotic cells; autophagosomes enclose cytoplasmic components for degradation in the lysosome/vacuole. Autophagosome formation requires two ubiquitin-like conjugation systems, the Atg12 and Atg8 systems, which are tightly associated with expansion of autophagosomal membrane. Previous studies have suggested that there is a hierarchy between these systems; the Atg12 system is located upstream of the Atg8 system in the context of Atg protein organization. However, the concrete molecular relationship is unclear. Here, we show using an in vitro Atg8 conjugation system that the Atg12-Atg5 conjugate, but not unconjugated Atg12 or Atg5, strongly enhances the formation of the other conjugate, Atg8-PE. The Atg12-Atg5 conjugate promotes the transfer of Atg8 from Atg3 to the substrate, phosphatidylethanolamine (PE), by stimulating the activity of Atg3. We also show that the Atg12-Atg5 conjugate interacts with both Atg3 and PE-containing liposomes. These results indicate that the Atg12-Atg5 conjugate is a ubiquitin-protein ligase (E3)-like enzyme for Atg8-PE conjugation reaction, distinctively promoting protein-lipid conjugation.
authors.affiliation: Division of Molecular Cell Biology, National Institute for Basic Biology, Myodaiji, Okazaki, Japan.
authors.forename: Takao
authors.initials: T
authors.lastname: Hanada
authors.forename: Nobuo N
authors.initials: NN
authors.lastname: Noda
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Satomi
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Ichimura
authors.forename: Yuko
authors.initials: Y
authors.lastname: Fujioka
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Takao
authors.forename: Fuyuhiko
authors.initials: F
authors.lastname: Inagaki
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Ohsumi
mesh_terms: D001343:Autophagy; D000071192:Autophagy-Related Protein 12; D000071187:Autophagy-Related Protein 5; D004926:Escherichia coli / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D008055:Lipids / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry; D008954:Models, Biological; D011499:Protein Processing, Post-Translational; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism / Q000502:physiology*; D013997:Time Factors; D025801:Ubiquitin; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*
chemical_list: C491969:ATG12 protein, S cerevisiae; C102268:ATG5 protein, S cerevisiae; D000071192:Autophagy-Related Protein 12; D000071187:Autophagy-Related Protein 5; D008055:Lipids; D008081:Liposomes; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; D044767:Ubiquitin-Protein Ligases