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Jenni A, Knüsel S, Nagar R, Benninger M, Häner R, Ferguson MAJ, Roditi I, Menon AK, Bütikofer P. Elimination of GPI2 suppresses glycosylphosphatidylinositol GlcNAc transferase activity and alters GPI glycan modification in Trypanosoma brucei. J Biol Chem 2021; 297:100977. [PMID: 34284059 PMCID: PMC8358704 DOI: 10.1016/j.jbc.2021.100977] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2021] [Revised: 06/20/2021] [Accepted: 07/16/2021] [Indexed: 01/14/2023] Open
Abstract
Many eukaryotic cell-surface proteins are post-translationally 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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Affiliation(s)
- Aurelio Jenni
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland; Graduate School for Chemical and Biomedical Sciences, University of Bern, Bern, Switzerland
| | - Sebastian Knüsel
- Institute of Cell Biology, University of Bern, Bern, Switzerland
| | - Rupa Nagar
- Wellcome Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | | | - Robert Häner
- Department for Chemistry and Biochemistry, University of Bern, Bern, Switzerland
| | - Michael A J Ferguson
- Wellcome Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Isabel Roditi
- Institute of Cell Biology, University of Bern, Bern, Switzerland
| | - Anant K Menon
- Department of Biochemistry, Weill Cornell Medical College, New York, New York, USA
| | - Peter Bütikofer
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland.
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Horáková E, Changmai P, Vancová M, Sobotka R, Van Den Abbeele J, Vanhollebeke B, Lukeš J. The Trypanosoma brucei TbHrg protein is a heme transporter involved in the regulation of stage-specific morphological transitions. J Biol Chem 2017; 292:6998-7010. [PMID: 28232490 DOI: 10.1074/jbc.m116.762997] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Revised: 02/21/2017] [Indexed: 12/27/2022] Open
Abstract
The human parasite Trypanosoma brucei does not synthesize heme de novo and instead relies entirely on heme supplied by its vertebrate host or its insect vector, the tsetse fly. In the host bloodstream T. brucei scavenges heme via haptoglobin-hemoglobin (HpHb) receptor-mediated endocytosis occurring in the flagellar pocket. However, in the procyclic developmental stage, in which T. brucei is confined to the tsetse fly midgut, this receptor is apparently not expressed, suggesting that T. brucei takes up heme by a different, unknown route. To define this alternative route, we functionally characterized heme transporter TbHrg in the procyclic stage. RNAi-induced down-regulation of TbHrg in heme-limited culture conditions resulted in slower proliferation, decreased cellular heme, and marked changes in cellular morphology so that the cells resemble mesocyclic trypomastigotes. Nevertheless, the TbHrg KO developed normally in the tsetse flies at rates comparable with wild-type cells. T. brucei cells overexpressing TbHrg displayed up-regulation of the early procyclin GPEET and down-regulation of the late procyclin EP1, two proteins coating the T. brucei surface in the procyclic stage. Light microscopy of immunostained TbHrg indicated localization to the flagellar membrane, and scanning electron microscopy revealed more intense TbHrg accumulation toward the flagellar pocket. Based on these findings, we postulate that T. brucei senses heme levels via the flagellar TbHrg protein. Heme deprivation in the tsetse fly anterior midgut might represent an environmental stimulus involved in the transformation of this important human parasite, possibly through metabolic remodeling.
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Affiliation(s)
- Eva Horáková
- From the Institute of Parasitology, Biology Center, Czech Academy of Sciences, 37005 České Budějovice (Budweis), Czech Republic
| | - Piya Changmai
- From the Institute of Parasitology, Biology Center, Czech Academy of Sciences, 37005 České Budějovice (Budweis), Czech Republic
| | - Marie Vancová
- From the Institute of Parasitology, Biology Center, Czech Academy of Sciences, 37005 České Budějovice (Budweis), Czech Republic.,Faculty of Sciences, University of South Bohemia, 37005 České Budějovice (Budweis), Czech Republic
| | - Roman Sobotka
- Faculty of Sciences, University of South Bohemia, 37005 České Budějovice (Budweis), Czech Republic.,Institute of Microbiology, Czech Academy of Sciences, 37981 Třeboň, Czech Republic
| | - Jan Van Den Abbeele
- Department of Biomedical Sciences, Unit of Veterinary Protozoology, Institute of Tropical Medicine, B2000 Antwerp, Belgium
| | - Benoit Vanhollebeke
- Institut de Biologie et de Médecine Moléculaires, Université Libre de Bruxelles, B6041 Gosselies, Belgium, and
| | - Julius Lukeš
- From the Institute of Parasitology, Biology Center, Czech Academy of Sciences, 37005 České Budějovice (Budweis), Czech Republic, .,Faculty of Sciences, University of South Bohemia, 37005 České Budějovice (Budweis), Czech Republic.,Canadian Institute for Advanced Research, Toronto, Ontario M5G 1Z8, Canada
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