Aberrant substrate engagement of the ER translocon triggers degradation by the Hrd1 ubiquitin ligase

J Cell Biol. 2012 Jun 11;197(6):761-73. doi: 10.1083/jcb.201203061.

Abstract

Little is known about quality control of proteins that aberrantly or persistently engage the endoplasmic reticulum (ER)-localized translocon en route to membrane localization or the secretory pathway. Hrd1 and Doa10, the primary ubiquitin ligases that function in ER-associated degradation (ERAD) in yeast, target distinct subsets of misfolded or otherwise abnormal proteins based primarily on degradation signal (degron) location. We report the surprising observation that fusing Deg1, a cytoplasmic degron normally recognized by Doa10, to the Sec62 membrane protein rendered the protein a Hrd1 substrate. Hrd1-dependent degradation occurred when Deg1-Sec62 aberrantly engaged the Sec61 translocon channel and underwent topological rearrangement. Mutations that prevent translocon engagement caused a reversion to Doa10-dependent degradation. Similarly, a variant of apolipoprotein B, a protein known to be cotranslocationally targeted for proteasomal degradation, was also a Hrd1 substrate. Hrd1 therefore likely plays a general role in targeting proteins that persistently associate with and potentially obstruct the translocon.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Cytoplasm / metabolism
  • Endopeptidase K / metabolism
  • Endoplasmic Reticulum / metabolism*
  • Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase / metabolism
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Protein Transport
  • Saccharomyces cerevisiae / enzymology
  • Saccharomyces cerevisiae / metabolism
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Ubiquitin / metabolism
  • Ubiquitin-Protein Ligases / genetics
  • Ubiquitin-Protein Ligases / metabolism*

Substances

  • Membrane Proteins
  • Saccharomyces cerevisiae Proteins
  • Ubiquitin
  • HRD1 protein, S cerevisiae
  • Ubiquitin-Protein Ligases
  • Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase
  • Endopeptidase K