title: Arginine68 is an essential residue for the C-terminal cleavage of human Atg8 family proteins.
abstract: BACKGROUND
  Autophagy is a conserved cellular process that degrades and recycles cytoplasmic components via a lysosomal pathway. The phosphatidylethanolamine (PE)-conjugation of the Atg8 protein plays an important role in the yeast autophagy process. In humans, six Atg8 homologs, including MAP1LC3A, MAP1LC3B, MAP1LC3C (refer to LC3A, LC3B, and LC3C hereafter), GABARAP, GABARAPL1, and GABARAPL2 have been reported. All of them can be conjugated to PE through a ubiquitin-like conjugation system, and be located to autophagosomes.
  
  
  RESULTS
  In this study, we found 3 new alternative splicing isoforms in LC3B, GABARAP, and GABARAPL1, (designated as LC3B-a, GABARAP-a and GABARAPL1-a, respectively). None of them can go through the PE-conjugation process and be located to autophagosomes. Interestingly, compared with LC3B, LC3B-a has a single amino acid (Arg68) deletion due to the NAGNAG alternative splicing in intron 3. Through structural simulations, we found that the C-terminal tail of LC3B-a is less mobile than that of LC3B, thus affecting its C-terminal cleavage by human ATG4 family proteins. Furthermore, we found that Arg68 is an essential residue facilitating the interaction between human Atg8 family proteins and ATG4B by forming a salt bridge with Asp171 of ATG4B. Depletion of this salt bridge reduces autophagosomes formation and autophagic flux under both normal and nutrition starvation conditions.
  
  
  CONCLUSIONS
  These results suggest Arg68 is an essential residue for the C-terminal cleavage of Atg8 family proteins during the autophagy process.
authors.affiliation: State Key Laboratory of Genetic Engineering; Institute of Genetics, School of Life Sciences, Fudan University, Shanghai 200433, China.
authors.forename: Chao
authors.initials: C
authors.lastname: Liu
authors.forename: Haijie
authors.initials: H
authors.lastname: Ma
authors.forename: Jiaxue
authors.initials: J
authors.lastname: Wu
authors.forename: Qiang
authors.initials: Q
authors.lastname: Huang
authors.forename: Jun O
authors.initials: JO
authors.lastname: Liu
authors.forename: Long
authors.initials: L
authors.lastname: Yu
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D001120:Arginine / Q000502:physiology*; D001343:Autophagy / Q000502:physiology*; D000071190:Autophagy-Related Protein 8 Family; D002478:Cells, Cultured; D006367:HeLa Cells; D006801:Humans; D008840:Microfilament Proteins / Q000378:metabolism*; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D010588:Phagosomes / Q000378:metabolism; D020033:Protein Isoforms / Q000378:metabolism; D059748:Proteolysis
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000071190:Autophagy-Related Protein 8 Family; C498698:GABARAPL2 protein, human; C502070:MAP1LC3B protein, human; D008840:Microfilament Proteins; D008869:Microtubule-Associated Proteins; D020033:Protein Isoforms; D001120:Arginine