1
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Duncan SM, Carbajo CG, Nagar R, Zhong Q, Breen C, Ferguson MAJ, Tiengwe C. Generation of a bloodstream form Trypanosoma brucei double glycosyltransferase null mutant competent in receptor-mediated endocytosis of transferrin. PLoS Pathog 2024; 20:e1012333. [PMID: 38935804 PMCID: PMC11236118 DOI: 10.1371/journal.ppat.1012333] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2024] [Revised: 07/10/2024] [Accepted: 06/10/2024] [Indexed: 06/29/2024] Open
Abstract
The bloodstream form of Trypanosoma brucei expresses large poly-N-acetyllactosamine (pNAL) chains on complex N-glycans of a subset of glycoproteins. It has been hypothesised that pNAL may be required for receptor-mediated endocytosis. African trypanosomes contain a unique family of glycosyltransferases, the GT67 family. Two of these, TbGT10 and TbGT8, have been shown to be involved in pNAL biosynthesis in bloodstream form Trypanosoma brucei, raising the possibility that deleting both enzymes simultaneously might abolish pNAL biosynthesis and provide clues to pNAL function and/or essentiality. In this paper, we describe the creation of a TbGT10 null mutant containing a single TbGT8 allele that can be excised upon the addition of rapamycin and, from that, a TbGT10 and TbGT8 double null mutant. These mutants were analysed by lectin blotting, glycopeptide methylation linkage analysis and flow cytometry. The data show that the mutants are defective, but not abrogated, in pNAL synthesis, suggesting that other GT67 family members can compensate to some degree for loss of TbGT10 and TbGT8. Despite there being residual pNAL synthesis in these mutants, certain glycoproteins appear to be particularly affected. These include the lysosomal CBP1B serine carboxypeptidase, cell surface ESAG2 and the ESAG6 subunit of the essential parasite transferrin receptor (TfR). The pNAL deficient TfR in the mutants continued to function normally with respect to protein stability, transferrin binding, receptor mediated endocytosis of transferrin and subcellular localisation. Further the pNAL deficient mutants were as viable as wild type parasites in vitro and in in vivo mouse infection experiments. Although we were able to reproduce the inhibition of transferrin uptake with high concentrations of pNAL structural analogues (N-acetylchito-oligosaccharides), this effect disappeared at lower concentrations that still inhibited tomato lectin uptake, i.e., at concentrations able to outcompete lectin-pNAL binding. Based on these findings, we recommend revision of the pNAL-dependent receptor mediated endocytosis hypothesis.
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Affiliation(s)
- Samuel M. Duncan
- Wellcome Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Carla Gilabert Carbajo
- Faculty of Natural Sciences, Department of Life Sciences, Imperial College London, London, United Kingdom
| | - Rupa Nagar
- Wellcome Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Qi Zhong
- Faculty of Natural Sciences, Department of Life Sciences, Imperial College London, London, United Kingdom
| | - Conor Breen
- Regeneron Biotech, Raheen Business Park, Limerick, Ireland
| | - Michael A. J. Ferguson
- Wellcome Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Calvin Tiengwe
- Faculty of Natural Sciences, Department of Life Sciences, Imperial College London, London, United Kingdom
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2
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Trajano-Silva LAM, Mule SN, Palmisano G. Molecular tools to regulate gene expression in Trypanosoma cruzi. Adv Clin Chem 2024; 120:169-190. [PMID: 38762241 DOI: 10.1016/bs.acc.2024.04.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/20/2024]
Abstract
Developing molecular strategies to manipulate gene expression in trypanosomatids is challenging, particularly with respect to the unique gene expression mechanisms adopted by these unicellular parasites, such as polycistronic mRNA transcription and multi-gene families. In the case of Trypanosoma cruzi (T. cruzi), the causative agent of Chagas Disease, the lack of RNA interference machinery further complicated functional genetic studies important for understanding parasitic biology and developing biomarkers and potential therapeutic targets. Therefore, alternative methods of performing knockout and/or endogenous labelling experiments were developed to identify and understand the function of proteins for survival and interaction with the host. In this review, we present the main tools for the genetic manipulation of T. cruzi, focusing on the Clustered Regularly Interspaced Short Palindromic Repeats Cas9-associated system technique widely used in this organism. Moreover, we highlight the importance of using these tools to elucidate the function of uncharacterized and glycosylated proteins. Further developments of these technologies will allow the identification of new biomarkers, therapeutic targets and potential vaccines against Chagas disease with greater efficiency and speed.
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Affiliation(s)
- Lays Adrianne M Trajano-Silva
- Glycoproteomic Laboratory, Parasitology Department, Institute of Biomedical Science II, University of Sao Paulo, Sao Paulo, Brazil
| | - Simon Ngao Mule
- Glycoproteomic Laboratory, Parasitology Department, Institute of Biomedical Science II, University of Sao Paulo, Sao Paulo, Brazil
| | - Giuseppe Palmisano
- Glycoproteomic Laboratory, Parasitology Department, Institute of Biomedical Science II, University of Sao Paulo, Sao Paulo, Brazil; School of Natural Sciences, Macquarie University, Sydney, NSW, Australia.
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3
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Ramírez AS, de Capitani M, Pesciullesi G, Kowal J, Bloch JS, Irobalieva RN, Reymond JL, Aebi M, Locher KP. Molecular basis for glycan recognition and reaction priming of eukaryotic oligosaccharyltransferase. Nat Commun 2022; 13:7296. [PMID: 36435935 PMCID: PMC9701220 DOI: 10.1038/s41467-022-35067-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Accepted: 11/17/2022] [Indexed: 11/28/2022] Open
Abstract
Oligosaccharyltransferase (OST) is the central enzyme of N-linked protein glycosylation. It catalyzes the transfer of a pre-assembled glycan, GlcNAc2Man9Glc3, from a dolichyl-pyrophosphate donor to acceptor sites in secretory proteins in the lumen of the endoplasmic reticulum. Precise recognition of the fully assembled glycan by OST is essential for the subsequent quality control steps of glycoprotein biosynthesis. However, the molecular basis of the OST-donor glycan interaction is unknown. Here we present cryo-EM structures of S. cerevisiae OST in distinct functional states. Our findings reveal that the terminal glucoses (Glc3) of a chemo-enzymatically generated donor glycan analog bind to a pocket formed by the non-catalytic subunits WBP1 and OST2. We further find that binding either donor or acceptor substrate leads to distinct primed states of OST, where subsequent binding of the other substrate triggers conformational changes required for catalysis. This alternate priming allows OST to efficiently process closely spaced N-glycosylation sites.
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Affiliation(s)
- Ana S. Ramírez
- grid.5801.c0000 0001 2156 2780Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule (ETH), Zürich, Switzerland
| | - Mario de Capitani
- grid.5734.50000 0001 0726 5157Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland
| | - Giorgio Pesciullesi
- grid.5734.50000 0001 0726 5157Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland
| | - Julia Kowal
- grid.5801.c0000 0001 2156 2780Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule (ETH), Zürich, Switzerland
| | - Joël S. Bloch
- grid.5801.c0000 0001 2156 2780Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule (ETH), Zürich, Switzerland
| | - Rossitza N. Irobalieva
- grid.5801.c0000 0001 2156 2780Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule (ETH), Zürich, Switzerland
| | - Jean-Louis Reymond
- grid.5734.50000 0001 0726 5157Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland
| | - Markus Aebi
- grid.5801.c0000 0001 2156 2780Institute of Microbiology, Eidgenössische Technische Hochschule (ETH), Zürich, Switzerland
| | - Kaspar P. Locher
- grid.5801.c0000 0001 2156 2780Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule (ETH), Zürich, Switzerland
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4
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Common and unique features of glycosylation and glycosyltransferases in African trypanosomes. Biochem J 2022; 479:1743-1758. [PMID: 36066312 PMCID: PMC9472816 DOI: 10.1042/bcj20210778] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2022] [Revised: 08/08/2022] [Accepted: 08/10/2022] [Indexed: 11/26/2022]
Abstract
Eukaryotic protein glycosylation is mediated by glycosyl- and oligosaccharyl-transferases. Here, we describe how African trypanosomes exhibit both evolutionary conservation and significant divergence compared with other eukaryotes in how they synthesise their glycoproteins. The kinetoplastid parasites have conserved components of the dolichol-cycle and oligosaccharyltransferases (OSTs) of protein N-glycosylation, and of glycosylphosphatidylinositol (GPI) anchor biosynthesis and transfer to protein. However, some components are missing, and they process and decorate their N-glycans and GPI anchors in unique ways. To do so, they appear to have evolved a distinct and functionally flexible glycosyltransferases (GT) family, the GT67 family, from an ancestral eukaryotic β3GT gene. The expansion and/or loss of GT67 genes appears to be dependent on parasite biology. Some appear to correlate with the obligate passage of parasites through an insect vector, suggesting they were acquired through GT67 gene expansion to assist insect vector (tsetse fly) colonisation. Others appear to have been lost in species that subsequently adopted contaminative transmission. We also highlight the recent discovery of a novel and essential GT11 family of kinetoplastid parasite fucosyltransferases that are uniquely localised to the mitochondria of Trypanosoma brucei and Leishmania major. The origins of these kinetoplastid FUT1 genes, and additional putative mitochondrial GT genes, are discussed.
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5
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Gallo GL, Valko A, Aguilar NH, Weisz AD, D'Alessio C. A novel fission yeast platform to model N-glycosylation and the bases of congenital disorders of glycosylation Type I. J Cell Sci 2021; 135:274232. [PMID: 34851357 DOI: 10.1242/jcs.259167] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2021] [Accepted: 11/18/2021] [Indexed: 11/20/2022] Open
Abstract
Congenital Disorders of Glycosylation Type I (CDG-I) are inherited human diseases caused by deficiencies in lipid-linked oligosaccharide (LLO) synthesis or the glycan transfer to proteins during N-glycosylation. We constructed a platform of 16 Schizosaccharomyces pombe mutant strains that synthesize all possible theoretical combinations of LLOs containing three to zero Glc and nine to five Man. The occurrence of unexpected LLOs suggested the requirement of specific Man residues for glucosyltransferases activities. We then quantified protein hypoglycosylation in each strain and found that in S. pombe the presence of Glc in the LLO is more relevant to the transfer efficiency than the amount of Man residues. Surprisingly, a decrease in the number of Man in glycans somehow improved the glycan transfer. The most severe hypoglycosylation was produced in cells completely lacking Glc and having a high number of Man. This deficiency could be reverted by expressing a single subunit OST with a broad range of substrate specificity. Our work shows the usefulness of this new S. pombe set of mutants as a platform to model the molecular bases of human CDG-I diseases.
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Affiliation(s)
- Giovanna L Gallo
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Fisiología, Biología Molecular y Celular, Instituto de Biociencias, Biotecnología y Biología Traslacional (iB3), Buenos Aires C1428EGA, Argentina.,Consejo Nacional de investigaciones Científicas y Técnicas (CONICET), Argentina.,Fundación Instituto Leloir, Buenos Aires, C1405BWE, Argentina
| | - Ayelen Valko
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Fisiología, Biología Molecular y Celular, Instituto de Biociencias, Biotecnología y Biología Traslacional (iB3), Buenos Aires C1428EGA, Argentina.,Consejo Nacional de investigaciones Científicas y Técnicas (CONICET), Argentina.,Fundación Instituto Leloir, Buenos Aires, C1405BWE, Argentina
| | - Nathalia Herrera Aguilar
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Fisiología, Biología Molecular y Celular, Instituto de Biociencias, Biotecnología y Biología Traslacional (iB3), Buenos Aires C1428EGA, Argentina.,Fundación Instituto Leloir, Buenos Aires, C1405BWE, Argentina
| | - Ariel D Weisz
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Fisiología, Biología Molecular y Celular, Instituto de Biociencias, Biotecnología y Biología Traslacional (iB3), Buenos Aires C1428EGA, Argentina
| | - Cecilia D'Alessio
- Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Fisiología, Biología Molecular y Celular, Instituto de Biociencias, Biotecnología y Biología Traslacional (iB3), Buenos Aires C1428EGA, Argentina.,Consejo Nacional de investigaciones Científicas y Técnicas (CONICET), Argentina
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6
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Duncan SM, Nagar R, Damerow M, Yashunsky DV, Buzzi B, Nikolaev AV, Ferguson MAJ. A Trypanosoma brucei β3 glycosyltransferase superfamily gene encodes a β1-6 GlcNAc-transferase mediating N-glycan and GPI anchor modification. J Biol Chem 2021; 297:101153. [PMID: 34478712 PMCID: PMC8477195 DOI: 10.1016/j.jbc.2021.101153] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 08/11/2021] [Accepted: 08/30/2021] [Indexed: 11/18/2022] Open
Abstract
The parasite Trypanosoma brucei exists in both a bloodstream form (BSF) and a procyclic form (PCF), which exhibit large carbohydrate extensions on the N-linked glycans and glycosylphosphatidylinositol (GPI) anchors, respectively. The parasite's glycoconjugate repertoire suggests at least 38 glycosyltransferase (GT) activities, 16 of which are currently uncharacterized. Here, we probe the function(s) of the uncharacterized GT67 glycosyltransferase family and a β3 glycosyltransferase (β3GT) superfamily gene, TbGT10. A BSF-null mutant, created by applying the diCre/loxP method in T. brucei for the first time, showed a fitness cost but was viable in vitro and in vivo and could differentiate into the PCF, demonstrating nonessentiality of TbGT10. The absence of TbGT10 impaired the elaboration of N-glycans and GPI anchor side chains in BSF and PCF parasites, respectively. Glycosylation defects included reduced BSF glycoprotein binding to the lectin ricin and monoclonal antibodies mAb139 and mAbCB1. The latter bind a carbohydrate epitope present on lysosomal glycoprotein p67 that we show here consists of (-6Galβ1-4GlcNAcβ1-)≥4 poly-N-acetyllactosamine repeats. Methylation linkage analysis of Pronase-digested glycopeptides isolated from BSF wild-type and TbGT10 null parasites showed a reduction in 6-O-substituted- and 3,6-di-O-substituted-Gal residues. These data define TbGT10 as a UDP-GlcNAc:βGal β1-6 GlcNAc-transferase. The dual role of TbGT10 in BSF N-glycan and PCF GPI-glycan elaboration is notable, and the β1-6 specificity of a β3GT superfamily gene product is unprecedented. The similar activities of trypanosome TbGT10 and higher-eukaryote I-branching enzyme (EC 2.4.1.150), which belong to glycosyltransferase families GT67 and GT14, respectively, in elaborating N-linked glycans, are a novel example of convergent evolution.
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Affiliation(s)
- Samuel M Duncan
- Wellcome Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Rupa Nagar
- Wellcome Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Manuela Damerow
- Wellcome Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Dmitry V Yashunsky
- Wellcome Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Benedetta Buzzi
- Wellcome Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Andrei V Nikolaev
- Wellcome Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Michael A J Ferguson
- Wellcome Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dundee, United Kingdom.
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7
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Wiktor M, Wiertelak W, Maszczak-Seneczko D, Balwierz PJ, Szulc B, Olczak M. Identification of novel potential interaction partners of UDP-galactose (SLC35A2), UDP-N-acetylglucosamine (SLC35A3) and an orphan (SLC35A4) nucleotide sugar transporters. J Proteomics 2021; 249:104321. [PMID: 34242836 DOI: 10.1016/j.jprot.2021.104321] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Revised: 07/01/2021] [Accepted: 07/02/2021] [Indexed: 10/20/2022]
Abstract
Nucleotide sugar transporters (NSTs) are ER and Golgi-resident members of the solute carrier 35 (SLC35) family which supply substrates for glycosylation by exchanging lumenal nucleotide monophosphates for cytosolic nucleotide sugars. Defective NSTs have been associated with congenital disorders of glycosylation (CDG), however, molecular basis of many types of CDG remains poorly characterized. To better understand the biology of NSTs, we identified potential interaction partners of UDP-galactose transporter (SLC35A2), UDP-N-acetylglucosamine transporter (SLC35A3) and an orphan nucleotide sugar transporter SLC35A4 of to date unassigned specificity. For this purpose, each of the SLC35A2-A4 proteins was used as a bait in four independent pull-down experiments and the identity of the immunoprecipitated material was discovered using MS techniques. From the candidate list obtained, we selected a few for which the interaction was confirmed in vitro using the NanoBiT system, a split luciferase-based luminescent technique. NSTs have been shown to interact with two ATPases (ATP2A2, ATP2C1), Golgi pH regulator B (GPR89B) and calcium channel (TMCO1), which may reflect the regulation of glycosylation by ion homeostasis, and with basigin (BSG). Our findings provide a starting point for the NST interaction network discovery in order to better understand how glycosylation is regulated and linked to other cellular processes. SIGNIFICANCE: Despite the facts that nucleotide sugar transporters are a key component of the protein glycosylation machinery, and deficiencies in their activity underlie serious metabolic diseases, biology, function and regulation of these essential proteins remain enigmatic. In this study we have advanced the field by identifying sets of new potential interaction partners for UDP-galactose transporter (SLC35A2), UDP-N-acetylglucosamine transporter (SLC35A3) and an orphan transporter SLC35A4 of yet undefined role. Several of these new interactions were additionally confirmed in vitro using the NanoBiT system, a split luciferase complementation assay. This work is also significant in that it addresses the overall challenge of discovering membrane protein interaction partners by a detailed comparison of 4 different co-immunoprecipitation strategies and by custom sample preparation and data processing workflows.
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Affiliation(s)
- Maciej Wiktor
- Laboratory of Biochemistry, Faculty of Biotechnology, University of Wrocław, Wrocław, Poland.
| | - Wojciech Wiertelak
- Laboratory of Biochemistry, Faculty of Biotechnology, University of Wrocław, Wrocław, Poland.
| | | | - Piotr Jan Balwierz
- Computational Regulatory Genomics, MRC-London Institute of Medical Sciences, London, United Kingdom.
| | - Bożena Szulc
- Laboratory of Biochemistry, Faculty of Biotechnology, University of Wrocław, Wrocław, Poland.
| | - Mariusz Olczak
- Laboratory of Biochemistry, Faculty of Biotechnology, University of Wrocław, Wrocław, Poland.
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8
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Tiengwe C, Koeller CM, Bangs JD. Endoplasmic reticulum-associated degradation and disposal of misfolded GPI-anchored proteins in Trypanosoma brucei. Mol Biol Cell 2018; 29:2397-2409. [PMID: 30091673 PMCID: PMC6233060 DOI: 10.1091/mbc.e18-06-0380] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Misfolded secretory proteins are retained by endoplasmic reticulum quality control (ERQC) and degraded in the proteasome by ER-associated degradation (ERAD). However, in yeast and mammals, misfolded glycosylphosphatidylinositol (GPI)-anchored proteins are preferentially degraded in the vacuole/lysosome. We investigate this process in the divergent eukaryotic pathogen Trypanosoma brucei using a misfolded GPI-anchored subunit (HA:E6) of the trypanosome transferrin receptor. HA:E6 is N-glycosylated and GPI-anchored and accumulates in the ER as aggregates. Treatment with MG132, a proteasome inhibitor, generates a smaller protected polypeptide (HA:E6*), consistent with turnover in the proteasome. HA:E6* partitions between membrane and cytosol fractions, and both pools are proteinase K-sensitive, indicating cytosolic disposition of membrane-associated HA:E6*. HA:E6* is de-N-glycosylated and has a full GPI-glycan structure from which dimyristoylglycerol has been removed, indicating that complete GPI removal is not a prerequisite for proteasomal degradation. However, HA:E6* is apparently not ubiquitin-modified. The trypanosome GPI anchor is a forward trafficking signal; thus the dynamic tension between ERQC and ER exit favors degradation by ERAD. These results differ markedly from the standard eukaryotic model systems and may indicate an evolutionary advantage related to pathogenesis.
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Affiliation(s)
- Calvin Tiengwe
- Department of Microbiology and Immunology, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, Buffalo, NY 14214
| | - Carolina M Koeller
- Department of Microbiology and Immunology, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, Buffalo, NY 14214
| | - James D Bangs
- Department of Microbiology and Immunology, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, Buffalo, NY 14214
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9
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Ramírez AS, Boilevin J, Biswas R, Gan BH, Janser D, Aebi M, Darbre T, Reymond JL, Locher KP. Characterization of the single-subunit oligosaccharyltransferase STT3A from Trypanosoma brucei using synthetic peptides and lipid-linked oligosaccharide analogs. Glycobiology 2018; 27:525-535. [PMID: 28204532 PMCID: PMC5421464 DOI: 10.1093/glycob/cwx017] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Accepted: 02/10/2017] [Indexed: 01/11/2023] Open
Abstract
The initial transfer of a complex glycan in protein N-glycosylation is catalyzed by oligosaccharyltransferase (OST), which is generally a multisubunit membrane protein complex in the endoplasmic reticulum but a single-subunit enzyme (ssOST) in some protists. To investigate the reaction mechanism of ssOST, we recombinantly expressed, purified and characterized the STT3A protein from Trypanosoma brucei (TbSTT3A). We analyzed the in vitro activity of TbSTT3A by synthesizing fluorescently labeled acceptor peptides as well as lipid-linked oligosaccharide (LLO) analogs containing a chitobiose moiety coupled to oligoprenyl carriers of distinct lengths (C10, C15, C20 and C25) and with different double bond stereochemistry. We found that in addition to proline, charged residues at the +1 position of the sequon inhibited glycan transfer. An acidic residue at the −2 position significantly increased catalytic turnover but was not essential, in contrast to the bacterial OST. While all synthetic LLO analogs were processed by TbSTT3A, the length of the polyprenyl tail, but not the stereochemistry of the double bonds, determined their apparent affinity. We also synthesized phosphonate analogs of the LLOs, which were found to be competitive inhibitors of the reaction, although with lower apparent affinity to TbSTT3A than the active pyrophosphate analogs.
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Affiliation(s)
- Ana S Ramírez
- Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule (ETH), CH-8093 Zürich, Switzerland
| | - Jérémy Boilevin
- Department of Chemistry and Biochemistry, University of Berne, CH-3012 Berne, Switzerland
| | - Rasomoy Biswas
- Department of Chemistry and Biochemistry, University of Berne, CH-3012 Berne, Switzerland
| | - Bee Ha Gan
- Department of Chemistry and Biochemistry, University of Berne, CH-3012 Berne, Switzerland
| | - Daniel Janser
- Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule (ETH), CH-8093 Zürich, Switzerland
| | - Markus Aebi
- Institute of Microbiology, Eidgenössische Technische Hochschule (ETH), CH-8093 Zürich, Switzerland
| | - Tamis Darbre
- Department of Chemistry and Biochemistry, University of Berne, CH-3012 Berne, Switzerland
| | - Jean-Louis Reymond
- Department of Chemistry and Biochemistry, University of Berne, CH-3012 Berne, Switzerland
| | - Kaspar P Locher
- Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule (ETH), CH-8093 Zürich, Switzerland
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10
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Jinnelov A, Ali L, Tinti M, Güther MLS, Ferguson MAJ. Single-subunit oligosaccharyltransferases of Trypanosoma brucei display different and predictable peptide acceptor specificities. J Biol Chem 2017; 292:20328-20341. [PMID: 28928222 PMCID: PMC5724017 DOI: 10.1074/jbc.m117.810945] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Revised: 09/13/2017] [Indexed: 11/10/2022] Open
Abstract
Trypanosoma brucei causes African trypanosomiasis and contains three full-length oligosaccharyltransferase (OST) genes; two of which, TbSTT3A and TbSTT3B, are expressed in the bloodstream form of the parasite. These OSTs have different peptide acceptor and lipid-linked oligosaccharide donor specificities, and trypanosomes do not follow many of the canonical rules developed for other eukaryotic N-glycosylation pathways, raising questions as to the basic architecture and detailed function of trypanosome OSTs. Here, we show by blue-native gel electrophoresis and stable isotope labeling in cell culture proteomics that the TbSTT3A and TbSTT3B proteins associate with each other in large complexes that contain no other detectable protein subunits. We probed the peptide acceptor specificities of the OSTs in vivo using a transgenic glycoprotein reporter system and performed glycoproteomics on endogenous parasite glycoproteins using sequential endoglycosidase H and peptide:N-glycosidase-F digestions. This allowed us to assess the relative occupancies of numerous N-glycosylation sites by endoglycosidase H-resistant N-glycans originating from Man5GlcNAc2-PP-dolichol transferred by TbSTT3A, and endoglycosidase H-sensitive N-glycans originating from Man9GlcNAc2-PP-dolichol transferred by TbSTT3B. Using machine learning, we assessed the features that best define TbSTT3A and TbSTT3B substrates in vivo and built an algorithm to predict the types of N-glycan most likely to predominate at all the putative N-glycosylation sites in the parasite proteome. Finally, molecular modeling was used to suggest why TbSTT3A has a distinct preference for sequons containing and/or flanked by acidic amino acid residues. Together, these studies provide insights into how a highly divergent eukaryote has re-wired protein N-glycosylation to provide protein sequence-specific N-glycan modifications. Data are available via ProteomeXchange with identifiers PXD007236, PXD007267, and PXD007268.
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Affiliation(s)
- Anders Jinnelov
- Wellcome Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
| | - Liaqat Ali
- Wellcome Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
| | - Michele Tinti
- Wellcome Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
| | - Maria Lucia S Güther
- Wellcome Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
| | - Michael A J Ferguson
- Wellcome Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom.
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11
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Poljak K, Breitling J, Gauss R, Rugarabamu G, Pellanda M, Aebi M. Analysis of substrate specificity of Trypanosoma brucei oligosaccharyltransferases (OSTs) by functional expression of domain-swapped chimeras in yeast. J Biol Chem 2017; 292:20342-20352. [PMID: 29042445 DOI: 10.1074/jbc.m117.811133] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Revised: 10/11/2017] [Indexed: 11/06/2022] Open
Abstract
N-Linked protein glycosylation is an essential and highly conserved post-translational modification in eukaryotes. The transfer of a glycan from a lipid-linked oligosaccharide (LLO) donor to the asparagine residue of a nascent polypeptide chain is catalyzed by an oligosaccharyltransferase (OST) in the lumen of the endoplasmic reticulum (ER). Trypanosoma brucei encodes three paralogue single-protein OSTs called TbSTT3A, TbSTT3B, and TbSTT3C that can functionally complement the Saccharomyces cerevisiae OST, making it an ideal experimental system to study the fundamental properties of OST activity. We characterized the LLO and polypeptide specificity of all three TbOST isoforms and their chimeric forms in the heterologous expression host S. cerevisiae where we were able to apply yeast genetic tools and newly developed glycoproteomics methods. We demonstrated that TbSTT3A accepted LLO substrates ranging from Man5GlcNAc2 to Man7GlcNAc2 In contrast, TbSTT3B required more complex precursors ranging from Man6GlcNAc2 to Glc3Man9GlcNAc2 structures, and TbSTT3C did not display any LLO preference. Sequence differences between the isoforms cluster in three distinct regions. We have swapped the individual regions between different OST proteins and identified region 2 to influence the specificity toward the LLO and region 1 to influence polypeptide substrate specificity. These results provide a basis to further investigate the molecular mechanisms and contribution of single amino acids in OST interaction with its substrates.
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Affiliation(s)
- Kristina Poljak
- Institute of Microbiology, ETH Zurich, Vladimir-Prelog-Weg 4, CH-8093 Zurich, Switzerland
| | - Jörg Breitling
- Institute of Microbiology, ETH Zurich, Vladimir-Prelog-Weg 4, CH-8093 Zurich, Switzerland
| | - Robert Gauss
- Institute of Microbiology, ETH Zurich, Vladimir-Prelog-Weg 4, CH-8093 Zurich, Switzerland
| | - George Rugarabamu
- Institute of Microbiology, ETH Zurich, Vladimir-Prelog-Weg 4, CH-8093 Zurich, Switzerland
| | - Mauro Pellanda
- Institute of Microbiology, ETH Zurich, Vladimir-Prelog-Weg 4, CH-8093 Zurich, Switzerland
| | - Markus Aebi
- Institute of Microbiology, ETH Zurich, Vladimir-Prelog-Weg 4, CH-8093 Zurich, Switzerland.
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12
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Ramírez AS, Boilevin J, Lin CW, Ha Gan B, Janser D, Aebi M, Darbre T, Reymond JL, Locher KP. Chemo-enzymatic synthesis of lipid-linked GlcNAc2Man5 oligosaccharides using recombinant Alg1, Alg2 and Alg11 proteins. Glycobiology 2017; 27:726-733. [PMID: 28575298 PMCID: PMC5881667 DOI: 10.1093/glycob/cwx045] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Revised: 05/10/2017] [Accepted: 05/27/2017] [Indexed: 11/14/2022] Open
Abstract
The biosynthesis of eukaryotic lipid-linked oligosaccharides (LLOs) that act as donor substrates in eukaryotic protein N-glycosylation starts on the cytoplasmic side of the endoplasmic reticulum and includes the sequential addition of five mannose units to dolichol-pyrophosphate-GlcNAc2. These reactions are catalyzed by the Alg1, Alg2 and Alg11 gene products and yield Dol-PP-GlcNAc2Man5, an LLO intermediate that is subsequently flipped to the lumen of the endoplasmic reticulum. While the purification of active Alg1 has previously been described, Alg11 and Alg2 have been mostly studied in vivo. We here describe the expression and purification of functional, full length Alg2 protein. Along with the purified soluble domains Alg1 and Alg11, we used Alg2 to chemo-enzymatically generate Dol-PP-GlcNAc2Man5 analogs starting from synthetic LLOs containing a chitobiose moiety coupled to oligoprenyl carriers of distinct lengths (C10, C15, C20 and C25). We found that while the addition of the first mannose unit by Alg1 was successful with all of the LLO molecules, the Alg2-catalyzed reaction was only efficient if the acceptor LLOs contained a sufficiently long lipid tail of four or five isoprenyl units (C20 and C25). Following conversion with Alg11, the resulting C20 or C25 -containing GlcNAc2Man5 LLO analogs were successfully used as donor substrates of purified single-subunit oligosaccharyltransferase STT3A from Trypanosoma brucei. Our results provide a chemo-enzymatic method for the generation of eukaryotic LLO analogs and are the basis of subsequent mechanistic studies of the enigmatic Alg2 reaction mechanism.
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Affiliation(s)
- Ana S Ramírez
- Department of Biology, Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule (ETH), Schafmattstrasse 20, CH-8093 Zürich, Switzerland
| | - Jérémy Boilevin
- Department of Chemistry and Biochemistry, University of Berne, CH-3012 Berne, Switzerland
| | - Chia-Wei Lin
- Institute of Microbiology, Eidgenössische Technische Hochschule (ETH), CH-8093 Zürich, Switzerland
| | - Bee Ha Gan
- Department of Chemistry and Biochemistry, University of Berne, CH-3012 Berne, Switzerland
| | - Daniel Janser
- Department of Biology, Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule (ETH), Schafmattstrasse 20, CH-8093 Zürich, Switzerland
| | - Markus Aebi
- Institute of Microbiology, Eidgenössische Technische Hochschule (ETH), CH-8093 Zürich, Switzerland
| | - Tamis Darbre
- Department of Chemistry and Biochemistry, University of Berne, CH-3012 Berne, Switzerland
| | - Jean-Louis Reymond
- Department of Chemistry and Biochemistry, University of Berne, CH-3012 Berne, Switzerland
| | - Kaspar P Locher
- Department of Biology, Institute of Molecular Biology and Biophysics, Eidgenössische Technische Hochschule (ETH), Schafmattstrasse 20, CH-8093 Zürich, Switzerland
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13
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Gottier P, Gonzalez-Salgado A, Menon AK, Liu YC, Acosta-Serrano A, Bütikofer P. RFT1 Protein Affects Glycosylphosphatidylinositol (GPI) Anchor Glycosylation. J Biol Chem 2016; 292:1103-1111. [PMID: 27927990 DOI: 10.1074/jbc.m116.758367] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2016] [Revised: 11/17/2016] [Indexed: 12/16/2022] Open
Abstract
The membrane protein RFT1 is essential for normal protein N-glycosylation, but its precise function is not known. RFT1 was originally proposed to translocate the glycolipid Man5GlcNAc2-PP-dolichol (needed to synthesize N-glycan precursors) across the endoplasmic reticulum membrane, but subsequent studies showed that it does not play a direct role in transport. In contrast to the situation in yeast, RFT1 is not essential for growth of the parasitic protozoan Trypanosoma brucei, enabling the study of its function in a null background. We now report that lack of T. brucei RFT1 (TbRFT1) not only affects protein N-glycosylation but also glycosylphosphatidylinositol (GPI) anchor side-chain modification. Analysis by immunoblotting, metabolic labeling, and mass spectrometry demonstrated that the major GPI-anchored proteins of T. brucei procyclic forms have truncated GPI anchor side chains in TbRFT1 null parasites when compared with wild-type cells, a defect that is corrected by expressing a tagged copy of TbRFT1 in the null background. In vivo and in vitro labeling experiments using radiolabeled GPI precursors showed that GPI underglycosylation was not the result of decreased formation of the GPI precursor lipid or defective galactosylation of GPI intermediates in the endoplasmic reticulum, but rather due to modifications that are expected to occur in the Golgi apparatus. Unexpectedly, immunofluorescence microscopy localized TbRFT1 to both the endoplasmic reticulum and the Golgi, consistent with the proposal that TbRFT1 plays a direct or indirect role in GPI anchor glycosylation in the Golgi apparatus. Our results implicate RFT1 in a wider range of glycosylation processes than previously appreciated.
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Affiliation(s)
- Petra Gottier
- From the Institute of Biochemistry and Molecular Medicine and.,Graduate School of Cellular and Biochemical Sciences, University of Bern, 3012 Bern, Switzerland
| | | | - Anant K Menon
- the Department of Biochemistry, Weill Cornell Medical College, New York, New York 10065, and
| | | | - Alvaro Acosta-Serrano
- the Departments of Parasitology and.,Vector Biology, Liverpool School of Tropical Medicine, Liverpool L3 5QA, United Kingdom
| | - Peter Bütikofer
- From the Institute of Biochemistry and Molecular Medicine and
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14
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Damerow M, Graalfs F, Güther MLS, Mehlert A, Izquierdo L, Ferguson MAJ. A Gene of the β3-Glycosyltransferase Family Encodes N-Acetylglucosaminyltransferase II Function in Trypanosoma brucei. J Biol Chem 2016; 291:13834-45. [PMID: 27189951 PMCID: PMC4919465 DOI: 10.1074/jbc.m116.733246] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2016] [Indexed: 11/06/2022] Open
Abstract
The bloodstream form of the human pathogen Trypanosoma brucei expresses oligomannose, paucimannose, and complex N-linked glycans, including some exceptionally large poly-N-acetyllactosamine-containing structures. Despite the presence of complex N-glycans in this organism, no homologues of the canonical N-acetylglucosaminyltransferase I or II genes can be found in the T. brucei genome. These genes encode the activities that initiate the elaboration of the Manα1-3 and Manα1-6 arms, respectively, of the conserved trimannosyl-N-acetylchitobiosyl core of N-linked glycans. Previously, we identified a highly divergent T. brucei N-acetylglucosaminyltransferase I (TbGnTI) among a set of putative T. brucei glycosyltransferase genes belonging to the β3-glycosyltransferase superfamily (Damerow, M., Rodrigues, J. A., Wu, D., Güther, M. L., Mehlert, A., and Ferguson, M. A. (2014) J. Biol. Chem. 289, 9328-9339). Here, we demonstrate that TbGT15, another member of the same β3-glycosyltransferase family, encodes an equally divergent N-acetylglucosaminyltransferase II (TbGnTII) activity. In contrast to multicellular organisms, where GnTII activity is essential, TbGnTII null mutants of T. brucei grow in culture and are still infectious to animals. Characterization of the large poly-N-acetyllactosamine containing N-glycans of the TbGnTII null mutants by methylation linkage analysis suggests that, in wild-type parasites, the Manα1-6 arm of the conserved trimannosyl core may carry predominantly linear poly-N-acetyllactosamine chains, whereas the Manα1-3 arm may carry predominantly branched poly-N-acetyllactosamine chains. These results provide further detail on the structure and biosynthesis of complex N-glycans in an important human pathogen and provide a second example of the adaptation by trypanosomes of β3-glycosyltransferase family members to catalyze β1-2 glycosidic linkages.
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Affiliation(s)
- Manuela Damerow
- From the Division of Biological Chemistry and Drug Discovery, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
| | - Frauke Graalfs
- From the Division of Biological Chemistry and Drug Discovery, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
| | - M Lucia S Güther
- From the Division of Biological Chemistry and Drug Discovery, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
| | - Angela Mehlert
- From the Division of Biological Chemistry and Drug Discovery, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
| | - Luis Izquierdo
- From the Division of Biological Chemistry and Drug Discovery, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
| | - Michael A J Ferguson
- From the Division of Biological Chemistry and Drug Discovery, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom
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15
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Zacchi LF, Schulz BL. SWATH-MS Glycoproteomics Reveals Consequences of Defects in the Glycosylation Machinery. Mol Cell Proteomics 2016; 15:2435-47. [PMID: 27094473 DOI: 10.1074/mcp.m115.056366] [Citation(s) in RCA: 80] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Indexed: 12/16/2022] Open
Abstract
Glycan macro- and microheterogeneity have profound impacts on protein folding and function. This heterogeneity can be regulated by physiological or environmental factors. However, unregulated heterogeneity can lead to disease, and mutations in the glycosylation process cause a growing number of Congenital Disorders of Glycosylation. We systematically studied how mutations in the N-glycosylation pathway lead to defects in mature proteins using all viable Saccharomyces cerevisiae strains with deletions in genes encoding Endoplasmic Reticulum lumenal mannosyltransferases (Alg3, Alg9, and Alg12), glucosyltransferases (Alg6, Alg8, and Die2/Alg10), or oligosaccharyltransferase subunits (Ost3, Ost5, and Ost6). To measure the changes in glycan macro- and microheterogeneity in mature proteins caused by these mutations we developed a SWATH-mass spectrometry glycoproteomics workflow. We measured glycan structures and occupancy on mature cell wall glycoproteins, and relative protein abundance, in the different mutants. All mutants showed decreased glycan occupancy and altered cell wall proteomes compared with wild-type cells. Mutations in earlier mannosyltransferase or glucosyltransferase steps of glycan biosynthesis had stronger hypoglycosylation phenotypes, but glucosyltransferase defects were more severe. ER mannosyltransferase mutants displayed substantial global changes in glycan microheterogeneity consistent with truncations in the glycan transferred to protein in these strains. Although ER glucosyltransferase and oligosaccharyltransferase subunit mutants broadly showed no change in glycan structures, ost3Δ cells had shorter glycan structures at some sites, consistent with increased protein quality control mannosidase processing in this severely hypoglycosylating mutant. This method allows facile relative quantitative glycoproteomics, and our results provide insights into global regulation of site-specific glycosylation.
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Affiliation(s)
- Lucia F Zacchi
- From the ‡School of Chemistry and Molecular Biosciences, The University of Queensland, St Lucia, Queensland, 4072, Australia; §Fundación Instituto Leloir, Avenida Patricias Argentinas 435, Ciudad Autónoma de Buenos Aires, 1405, Argentina
| | - Benjamin L Schulz
- From the ‡School of Chemistry and Molecular Biosciences, The University of Queensland, St Lucia, Queensland, 4072, Australia;
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16
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Zacchi LF, Schulz BL. N-glycoprotein macroheterogeneity: biological implications and proteomic characterization. Glycoconj J 2015; 33:359-76. [DOI: 10.1007/s10719-015-9641-3] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2015] [Revised: 11/04/2015] [Accepted: 11/20/2015] [Indexed: 10/22/2022]
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17
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Izquierdo L, Acosta-Serrano A, Mehlert A, Ferguson MA. Identification of a glycosylphosphatidylinositol anchor-modifying β1-3 galactosyltransferase in Trypanosoma brucei. Glycobiology 2014; 25:438-47. [PMID: 25467966 PMCID: PMC4339879 DOI: 10.1093/glycob/cwu131] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Trypanosoma brucei is the causative agent of human African sleeping sickness and the cattle disease nagana. Trypanosoma brucei is dependent on glycoproteins for its survival and infectivity throughout its life cycle. Here we report the functional characterization of TbGT3, a glycosyltransferase expressed in the bloodstream and procyclic form of the parasite. Bloodstream and procyclic form TbGT3 conditional null mutants were created and both exhibited normal growth under permissive and nonpermissive conditions. Under nonpermissive conditions, the normal glycosylation of the major glycoprotein of bloodstream form T. brucei, the variant surface glycoprotein and the absence of major alterations in lectin binding to other glycoproteins suggested that the major function of TbGT3 occurs in the procyclic form of the parasite. Consistent with this, the major surface glycoprotein of the procyclic form, procyclin, exhibited a marked reduction in molecular weight due to changes in glycosylphosphatidylinositol (GPI) anchor side chains. Structural analysis of the mutant procyclin GPI anchors indicated that TbGT3 encodes a UDP-Gal: β-GlcNAc-GPI β1-3 Gal transferase. Despite the alterations in GPI anchor side chains, TbGT3 conditional null mutants remained infectious to tsetse flies under nonpermissive conditions.
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Affiliation(s)
- Luis Izquierdo
- Division of Biological Chemistry and Drug Discovery, The College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK Barcelona Centre for International Health Research, CRESIB, Hospital Clínic-Universitat de Barcelona, Barcelona 08036, Spain
| | - Alvaro Acosta-Serrano
- Department of Parasitology Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool L3 5QA, UK
| | - Angela Mehlert
- Division of Biological Chemistry and Drug Discovery, The College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Michael Aj Ferguson
- Division of Biological Chemistry and Drug Discovery, The College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
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18
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Damerow M, Rodrigues JA, Wu D, Güther MLS, Mehlert A, Ferguson MAJ. Identification and functional characterization of a highly divergent N-acetylglucosaminyltransferase I (TbGnTI) in Trypanosoma brucei. J Biol Chem 2014; 289:9328-39. [PMID: 24550396 PMCID: PMC3979372 DOI: 10.1074/jbc.m114.555029] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Trypanosoma brucei expresses a diverse repertoire of N-glycans, ranging from oligomannose and paucimannose structures to exceptionally large complex N-glycans. Despite the presence of the latter, no obvious homologues of known β1–4-galactosyltransferase or β1–2- or β1–6-N-acetylglucosaminyltransferase genes have been found in the parasite genome. However, we previously reported a family of putative UDP-sugar-dependent glycosyltransferases with similarity to the mammalian β1–3-glycosyltransferase family. Here we characterize one of these genes, TbGT11, and show that it encodes a Golgi apparatus resident UDP-GlcNAc:α3-d-mannoside β1–2-N-acetylglucosaminyltransferase I activity (TbGnTI). The bloodstream-form TbGT11 null mutant exhibited significantly modified protein N-glycans but normal growth in vitro and infectivity to rodents. In contrast to multicellular organisms, where the GnTI reaction is essential for biosynthesis of both complex and hybrid N-glycans, T. brucei TbGT11 null mutants expressed atypical “pseudohybrid” glycans, indicating that TbGnTII activity is not dependent on prior TbGnTI action. Using a functional in vitro assay, we showed that TbGnTI transfers UDP-GlcNAc to biantennary Man3GlcNAc2, but not to triantennary Man5GlcNAc2, which is the preferred substrate for metazoan GnTIs. Sequence alignment reveals that the T. brucei enzyme is far removed from the metazoan GnTI family and suggests that the parasite has adapted the β3-glycosyltransferase family to catalyze β1–2 linkages.
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Affiliation(s)
- Manuela Damerow
- From the Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom and
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19
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Two distinct N-glycosylation pathways process the Haloferax volcanii S-layer glycoprotein upon changes in environmental salinity. mBio 2013; 4:e00716-13. [PMID: 24194539 PMCID: PMC3892788 DOI: 10.1128/mbio.00716-13] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
N-glycosylation in Archaea presents aspects of this posttranslational modification not seen in either Eukarya or Bacteria. In the haloarchaeon Haloferax volcanii, the surface (S)-layer glycoprotein can be simultaneously modified by two different N-glycans. Asn-13 and Asn-83 are modified by a pentasaccharide, whereas Asn-498 is modified by a tetrasaccharide of distinct composition, with N-glycosylation at this position being related to environmental conditions. Specifically, N-glycosylation of Asn-498 is detected when cells are grown in the presence of 1.75 but not 3.4 M NaCl. While deletion of genes encoding components of the pentasaccharide assembly pathway had no effect on the biosynthesis of the tetrasaccharide bound to Asn-498, deletion of genes within the cluster spanning HVO_2046 to HVO_2061 interfered with the assembly and attachment of the Asn-498-linked tetrasaccharide. Transfer of the “low-salt” tetrasaccharide from the dolichol phosphate carrier upon which it is assembled to S-layer glycoprotein Asn-498 did not require AglB, the oligosaccharyltransferase responsible for pentasaccharide attachment to Asn-13 and Asn-83. Finally, although biogenesis of the low-salt tetrasaccharide is barely discernible upon growth at the elevated salinity, this glycan was readily detected under such conditions in strains deleted of pentasaccharide biosynthesis pathway genes, indicative of cross talk between the two N-glycosylation pathways. In the haloarchaeon Haloferax volcanii, originally from the Dead Sea, the pathway responsible for the assembly and attachment of a pentasaccharide to the S-layer glycoprotein, a well-studied glycoprotein in this species, has been described. More recently, it was shown that in response to growth in low salinity, the same glycoprotein is modified by a novel tetrasaccharide. In the present study, numerous components of the pathway used to synthesize this “low-salt” tetrasaccharide are described. As such, this represents the first report of two N-glycosylation pathways able to simultaneously modify a single protein as a function of environmental salinity. Moreover, and to the best of our knowledge, the ability to N-glycosylate the same protein with different and unrelated glycans has not been observed in either Eukarya or Bacteria or indeed beyond the halophilic archaea, for which similar dual modification of the Halobacterium salinarum S-layer glycoprotein was reported.
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20
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Aebi M. N-linked protein glycosylation in the ER. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2013; 1833:2430-7. [PMID: 23583305 DOI: 10.1016/j.bbamcr.2013.04.001] [Citation(s) in RCA: 484] [Impact Index Per Article: 44.0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 01/10/2013] [Revised: 03/25/2013] [Accepted: 04/01/2013] [Indexed: 01/18/2023]
Abstract
N-linked protein glycosylation in the endoplasmic reticulum (ER) is a conserved two phase process in eukaryotic cells. It involves the assembly of an oligosaccharide on a lipid carrier, dolichylpyrophosphate and the transfer of the oligosaccharide to selected asparagine residues of polypeptides that have entered the lumen of the ER. The assembly of the oligosaccharide (LLO) takes place at the ER membrane and requires the activity of several specific glycosyltransferases. The biosynthesis of the LLO initiates at the cytoplasmic side of the ER membrane and terminates in the lumen where oligosaccharyltransferase (OST) selects N-X-S/T sequons of polypeptide and generates the N-glycosidic linkage between the side chain amide of asparagine and the oligosaccharide. The N-glycosylation pathway in the ER modifies a multitude of proteins at one or more asparagine residues with a unique carbohydrate structure that is used as a signalling molecule in their folding pathway. In a later stage of glycoprotein processing, the same systemic modification is used in the Golgi compartment, but in this process, remodelling of the N-linked glycans in a protein-, cell-type and species specific manner generates the high structural diversity of N-linked glycans observed in eukaryotic organisms. This article summarizes the current knowledge of the N-glycosylation pathway in the ER that results in the covalent attachment of an oligosaccharide to asparagine residues of polypeptide chains and focuses on the model organism Saccharomyces cerevisiae. This article is part of a Special Issue entitled: Functional and structural diversity of endoplasmic reticulum.
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Affiliation(s)
- Markus Aebi
- Department of Biology, Institute of Microbiology, Zurich, Switzerland.
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21
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Intracellular trafficking and glycobiology of TbPDI2, a stage-specific protein disulfide isomerase in Trypanosoma brucei. EUKARYOTIC CELL 2012; 12:132-41. [PMID: 23159520 DOI: 10.1128/ec.00293-12] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Trypanosoma brucei protein disulfide isomerase 2 (TbPDI2) is a bloodstream stage-specific lumenal endoplasmic reticulum (ER) glycoprotein. ER localization is dependent on the TbPDI2 C-terminal tetrapeptide (KQDL) and is mediated by TbERD2, an orthologue of the yeast ER retrieval receptor. Consistent with this function, TbERD2 localizes prominently to ER exit sites, and RNA interference (RNAi) knockdown results in specific secretion of a surrogate ER retention reporter, BiPN:KQDL. TbPDI2 is highly N-glycosylated and is reactive with tomato lectin, suggesting the presence of poly-N-acetyllactosamine modifications, which are common on lyso/endosomal proteins in trypanosomes but are inconsistent with ER localization. However, TbPDI2 is reactive with tomato lectin immediately following biosynthesis-far too rapidly for transport to the Golgi compartment, the site of poly-N-acetyllactosamine addition. TbPDI2 also fails to react with Erythrina cristagalli lectin, confirming the absence of terminal N-acetyllactosamine units. We propose that tomato lectin binds the Manβ1-4GlcNAcβ1-4GlcNAc trisaccharide core of paucimannose glycans on both newly synthesized and mature TbPDI2. Consistent with this proposal, α-mannosidase treatment renders oligomannose N-glycans on the T. brucei cathepsin L orthologue TbCatL reactive with tomato lectin. These findings resolve contradictory evidence on the location and glycobiology of TbPDI2 and provide a cautionary note on the use of tomato lectin as a poly-N-acetyllactosamine-specific reagent.
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