Golgi-situated endoplasmic reticulum α-1, 2-mannosidase contributes to the retrieval of ERAD substrates through a direct interaction with γ-COP

Mol Biol Cell. 2013 Apr;24(8):1111-21. doi: 10.1091/mbc.E12-12-0886. Epub 2013 Feb 20.


Endoplasmic reticulum (ER) α-1, 2-mannosidase (ERManI) contributes to ER-associated protein degradation (ERAD) by initiating the formation of degradation signals on misfolded N-linked glycoproteins. Despite its inferred intracellular location, we recently discovered that the mammalian homologue is actually localized to the Golgi complex. In the present study, the functional role of Golgi-situated ERManI was investigated. Mass spectrometry analysis and coimmunoprecipitation (co-IP) identified a direct interaction between ERManI and γ-COP, the gamma subunit of coat protein complex I (COPI) that is responsible for Golgi-to-ER retrograde cargo transport. The functional relationship was validated by the requirement of both ERManI and γ-COP to support efficient intracellular clearance of the classical ERAD substrate, null Hong Kong (NHK). In addition, site-directed mutagenesis of suspected γ-COP-binding motifs in the cytoplasmic tail of ERManI was sufficient to disrupt the physical interaction and ablate NHK degradation. Moreover, a physical interaction between NHK, ERManI, and γ-COP was identified by co-IP and Western blotting. RNA interference-mediated knockdown of γ-COP enhanced the association between ERManI and NHK, while diminishing the efficiency of ERAD. Based on these findings, a model is proposed in which ERManI and γ-COP contribute to a Golgi-based quality control module that facilitates the retrieval of captured ERAD substrates back to the ER.

Publication types

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

MeSH terms

  • Amino Acid Substitution
  • COP-Coated Vesicles / metabolism
  • Coat Protein Complex I / chemistry
  • Coat Protein Complex I / genetics
  • Coat Protein Complex I / metabolism*
  • Endoplasmic Reticulum-Associated Degradation*
  • Golgi Apparatus / enzymology*
  • HeLa Cells
  • Humans
  • MCF-7 Cells
  • Mannosidases / chemistry
  • Mannosidases / metabolism*
  • Mutagenesis, Site-Directed
  • Protein Binding
  • Protein Interaction Domains and Motifs
  • Protein Subunits / chemistry
  • Protein Subunits / metabolism*
  • Protein Transport


  • Coat Protein Complex I
  • Protein Subunits
  • MAN1B1 protein, human
  • Mannosidases