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Elimination of GPI2 suppresses glycosylphosphatidylinositol GlcNAc transferase activity and alters GPI glycan modification in Trypanosoma brucei

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Jenni Aurelio, Knüsel Sebastian, Nagar Rupa, Benninger Mattias, Häner Robert, Ferguson Michael A.J., Roditi Isabel, Menon Anant K., Bütikofer Peter,
Project Molecular identification of lipid transporters for protein glycosylation
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Original article (peer-reviewed)

Journal Journal of Biological Chemistry
Volume (Issue) 297(2)
Page(s) 100977 - 100977
Title of proceedings Journal of Biological Chemistry
DOI 10.1016/j.jbc.2021.100977

Open Access

URL http://doi.org/10.1016/j.jbc.2021.100977
Type of Open Access Publisher (Gold Open Access)

Abstract

Many eukaryotic cell-surface proteins are posttranslationally modified by a glycosylphosphatidylinositol (GPI) moiety that anchors them to the cell membrane. The biosynthesis of GPI anchors is initiated in the endoplasmic reticulum by transfer of GlcNAc from UDP-GlcNAc to phosphatidylinositol. This reaction is catalyzed by GPI GlcNAc transferase, a multisubunit complex comprising the catalytic subunit Gpi3/PIG-A as well as at least five other subunits, including the hydrophobic protein Gpi2, which is essential for the activity of the complex in yeast and mammals, but the function of which is not known. To investigate the role of Gpi2, we exploited Trypanosoma brucei (Tb), an early diverging eukaryote and important model organism that initially provided the first insights into GPI structure and biosynthesis. We generated insect-stage (procyclic) trypanosomes that lack TbGPI2 and found that in TbGPI2-null parasites, (i) GPI GlcNAc transferase activity is reduced, but not lost, in contrast with yeast and human cells, (ii) the GPI GlcNAc transferase complex persists, but its architecture is affected, with loss of at least the TbGPI1 subunit, and (iii) the GPI anchors of procyclins, the major surface proteins, are underglycosylated when compared with their WT counterparts, indicating the importance of TbGPI2 for reactions that occur in the Golgi apparatus. Immunofluorescence microscopy localized TbGPI2 not only to the endoplasmic reticulum but also to the Golgi apparatus, suggesting that in addition to its expected function as a subunit of the GPI GlcNAc transferase complex, TbGPI2 may have an enigmatic noncanonical role in Golgi-localized GPI anchor modification in trypanosomes.
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