N-terminal arginylation generates a bimodal degron that modulates autophagic proteolysis

Proc Natl Acad Sci U S A. 2018 Mar 20;115(12):E2716-E2724. doi: 10.1073/pnas.1719110115. Epub 2018 Mar 5.


The conjugation of amino acids to the protein N termini is universally observed in eukaryotes and prokaryotes, yet its functions remain poorly understood. In eukaryotes, the amino acid l-arginine (l-Arg) is conjugated to N-terminal Asp (Nt-Asp), Glu, Gln, Asn, and Cys, directly or associated with posttranslational modifications. Following Nt-arginylation, the Nt-Arg is recognized by UBR boxes of N-recognins such as UBR1, UBR2, UBR4/p600, and UBR5/EDD, leading to substrate ubiquitination and proteasomal degradation via the N-end rule pathway. It has been a mystery, however, why studies for the past five decades identified only a handful of Nt-arginylated substrates in mammals, although five of 20 principal amino acids are eligible for arginylation. Here, we show that the Nt-Arg functions as a bimodal degron that directs substrates to either the ubiquitin (Ub)-proteasome system (UPS) or macroautophagy depending on physiological states. In normal conditions, the arginylated forms of proteolytic cleavage products, D101-CDC6 and D1156-BRCA1, are targeted to UBR box-containing N-recognins and degraded by the proteasome. However, when proteostasis by the UPS is perturbed, their Nt-Arg redirects these otherwise cellular wastes to macroautophagy through its binding to the ZZ domain of the autophagic adaptor p62/STQSM/Sequestosome-1. Upon binding to the Nt-Arg, p62 acts as an autophagic N-recognin that undergoes self-polymerization, facilitating cargo collection and lysosomal degradation of p62-cargo complexes. A chemical mimic of Nt-Arg redirects Ub-conjugated substrates from the UPS to macroautophagy and promotes their lysosomal degradation. Our results suggest that the Nt-Arg proteome of arginylated proteins contributes to reprogramming global proteolytic flux under stresses.

Keywords: ATE1 R-transferase; N-end rule pathway; macroautophagy; p62/STQSM/Sequestosome-1; ubiquitin-proteasome system.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aminoacyltransferases / genetics
  • Aminoacyltransferases / metabolism
  • Animals
  • Arginine / metabolism*
  • Autophagy / drug effects
  • Autophagy / physiology*
  • BRCA1 Protein / metabolism
  • Cell Cycle Proteins / metabolism*
  • Female
  • HEK293 Cells
  • HeLa Cells
  • Humans
  • Hydroxychloroquine / pharmacology
  • Mice
  • Mice, Inbred C57BL
  • Nuclear Proteins / metabolism*
  • Proteasome Endopeptidase Complex / metabolism
  • Protein Domains
  • Proteolysis*
  • RNA-Binding Proteins / metabolism*
  • Ubiquitin / metabolism


  • BRCA1 Protein
  • BRCA1 protein, human
  • CDC6 protein, human
  • Cell Cycle Proteins
  • Nuclear Proteins
  • P62 protein, human
  • RNA-Binding Proteins
  • Ubiquitin
  • Hydroxychloroquine
  • Arginine
  • Aminoacyltransferases
  • Ate1 protein, mouse
  • Proteasome Endopeptidase Complex