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Processing of autophagic protein LC3 by the 20S proteasome.

Ubiquitin-proteasome system and autophagy are the two major mechanisms for protein degradation in eukaryotic cells. LC3, a ubiquitin-like protein, plays an essential role in autophagy through its ability to be conjugated to phosphatidylethanolamine. In this study, we discovered a novel LC3-processing activity, and biochemically purified the 20S proteasome as the responsible enzyme. Processing of LC3 by the 20S proteasome is ATP- and ubiquitin-independent, and requires both the N-terminal helices and the ubiquitin fold of LC3; addition of the N-terminal helices of LC3 to the N terminus of ubiquitin renders ubiquitin susceptible to 20S proteasomal activity. Further, the 20S proteasome processes LC3 in a stepwise manner, it first cleaves LC3 within its ubiquitin fold and thus disrupts the conjugation function of LC3; subsequently and especially at high concentrations of the proteasome, LC3 is completely degraded. Intriguingly, proteolysis of LC3 by the 20S proteasome can be inhibited by p62, an LC3-binding protein that mediates autophagic degradation of polyubiquitin aggregates in cells. Therefore, our study implicates a potential mechanism underlying interplay between the proteasomal and autophagic pathways. This study also provides biochemical evidence suggesting relevance of the controversial ubiquitin-independent proteolytic activity of the 20S proteasome.

Pubmed ID: 20061800


  • Gao Z
  • Gammoh N
  • Wong PM
  • Erdjument-Bromage H
  • Tempst P
  • Jiang X



Publication Data

January 29, 2010

Associated Grants


Mesh Terms

  • Adaptor Proteins, Signal Transducing
  • Animals
  • Autophagy
  • Cell Extracts
  • Cells, Cultured
  • Cysteine Proteinase Inhibitors
  • HeLa Cells
  • Humans
  • Leupeptins
  • Mice
  • Microtubule-Associated Proteins
  • Proteasome Endopeptidase Complex
  • Proteasome Inhibitors
  • Protein Binding
  • Protein Folding
  • Protein Processing, Post-Translational
  • Protein Structure, Tertiary
  • Substrate Specificity
  • Ubiquitin
  • Ubiquitination