Calnexin mediates the maturation of GPI-anchors through ER retention

J Biol Chem. 2020 Nov 27;295(48):16393-16410. doi: 10.1074/jbc.RA120.015577. Epub 2020 Sep 23.


The protein folding and lipid moiety status of glycosylphosphatidylinositol-anchored proteins (GPI-APs) are monitored in the endoplasmic reticulum (ER), with calnexin playing dual roles in the maturation of GPI-APs. In the present study, we investigated the functions of calnexin in the quality control and lipid remodeling of GPI-APs in the ER. By directly binding the N-glycan on proteins, calnexin was observed to efficiently retain GPI-APs in the ER until they were correctly folded. In addition, sufficient ER retention time was crucial for GPI-inositol deacylation, which is mediated by post-GPI attachment protein 1 (PGAP1). Once the calnexin/calreticulin cycle was disrupted, misfolded and inositol-acylated GPI-APs could not be retained in the ER and were exposed on the plasma membrane. In calnexin/calreticulin-deficient cells, endogenous GPI-anchored alkaline phosphatase was expressed on the cell surface, but its activity was significantly decreased. ER stress induced surface expression of misfolded GPI-APs, but proper GPI-inositol deacylation occurred due to the extended time that they were retained in the ER. Our results indicate that calnexin-mediated ER quality control systems for GPI-APs are necessary for both protein folding and GPI-inositol deacylation.

Keywords: ER quality control; Endoplasmic reticulum; endoplasmic reticulum (ER); glycobiology; glycosylphosphatidylinositol; glycosylphosphatidylinositol (GPI anchor); lipid remodeling; protein folding.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Calnexin / genetics
  • Calnexin / metabolism*
  • Cell Membrane / genetics
  • Cell Membrane / metabolism*
  • Endoplasmic Reticulum / genetics
  • Endoplasmic Reticulum / metabolism*
  • HEK293 Cells
  • Humans
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Oligosaccharides / genetics
  • Oligosaccharides / metabolism*
  • Phosphoric Monoester Hydrolases / genetics
  • Phosphoric Monoester Hydrolases / metabolism
  • Protein Folding*


  • (6-O-aminoethylphosphonato-mannopyranosyl)-(1-2)-mannopyranosyl-(1-6)-mannopyranosyl-(1-4)-(2-amino-2-deoxyglucopyranosyl)-(1-6)-1-O-(1,2-di-O-octadecanoyl-sn-glyceryl-phosphonato)-myo-inositol
  • CANX protein, human
  • Membrane Proteins
  • Oligosaccharides
  • Calnexin
  • PGAP1 protein, human
  • Phosphoric Monoester Hydrolases