Ethanolamine-phosphate on the second mannose is a preferential bridge for some GPI-anchored proteins

EMBO Rep. 2022 Jul 5;23(7):e54352. doi: 10.15252/embr.202154352. Epub 2022 May 23.


Glycosylphosphatidylinositols (GPIs) are glycolipids that anchor many proteins (GPI-APs) on the cell surface. The core glycan of GPI precursor has three mannoses, which in mammals, are all modified by ethanolamine-phosphate (EthN-P). It is postulated that EthN-P on the third mannose (EthN-P-Man3) is the bridge between GPI and the protein and the second (EthN-P-Man2) is removed after GPI-protein attachment. However, EthN-P-Man2 may not be always transient, as mutations of PIGG, the enzyme that transfers EthN-P to Man2, result in inherited GPI deficiencies (IGDs), characterized by neuronal dysfunctions. Here, we show that EthN-P on Man2 is the preferential bridge in some GPI-APs, among them, the Ect-5'-nucleotidase and Netrin G2. We find that CD59, a GPI-AP, is attached via EthN-P-Man2 both in PIGB-knockout cells, in which GPI lacks Man3, and with a small fraction in wild-type cells. Our findings modify the current view of GPI anchoring and provide a mechanistic basis for IGDs caused by PIGG mutations.

Keywords: CD73; PIGB; PIGG; inherited GPI deficiency; mass spectrometry.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Ethanolamines / metabolism
  • GPI-Linked Proteins / genetics
  • Glycosylphosphatidylinositols* / genetics
  • Glycosylphosphatidylinositols* / metabolism
  • Mammals / metabolism
  • Mannose* / metabolism
  • Phosphates


  • Ethanolamines
  • GPI-Linked Proteins
  • Glycosylphosphatidylinositols
  • Phosphates
  • Mannose