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Nakanishi M, Takeguchi M, Takezaki R, Hino M, Nomoto H. Loss of complex-type N-linked glycans attenuates maximum cell density and susceptibility to human serum of Trypanosoma brucei brucei. Parasitol Int 2024; 101:102874. [PMID: 38417735 DOI: 10.1016/j.parint.2024.102874] [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] [Received: 09/05/2023] [Revised: 01/09/2024] [Accepted: 02/24/2024] [Indexed: 03/01/2024]
Abstract
Trypanosoma brucei brucei is a parasitic protist that expresses cell surface proteins modified with complex-type N-linked glycan (NLG), like multicellular organisms. However, little is known about the role of complex-type NLG. In T. b. brucei, it has been shown that either one of the glycosyltransferases, TbGT11 or TbGT15, is sufficient to initiate the synthesis of complex-type NLG. To clarify the role of complex-type NLG, it is necessary to generate cells lacking both enzymes. Therefore, we deleted TbGT11 and TbGT15 from the genome of T. b. brucei for the phenotypic examination. The mutant strain grew in culture, with reduced maximum cell density; showed decreased susceptibility to normal human serum, which contains trypanolytic factors; and lacked uptake of the haptoglobin-hemoglobin complex. These data indicate that protein modification by complex-type NLG is not essential but is required for receptor function.
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Affiliation(s)
- Masayuki Nakanishi
- Laboratory of Biochemistry, School of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan.
| | - Masaki Takeguchi
- Laboratory of Biochemistry, School of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan
| | - Reo Takezaki
- Laboratory of Biochemistry, School of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan
| | - Mami Hino
- Laboratory of Biochemistry, School of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan.
| | - Hiroshi Nomoto
- Laboratory of Biochemistry, School of Pharmaceutical Sciences, Matsuyama University, Matsuyama, Ehime 790-8578, Japan.
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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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Senjor E, Pirro M, Švajger U, Prunk M, Sabotič J, Jewett A, Hensbergen PJ, Perišić Nanut M, Kos J. Different glycosylation profiles of cystatin F alter the cytotoxic potential of natural killer cells. Cell Mol Life Sci 2023; 81:8. [PMID: 38092995 PMCID: PMC10719177 DOI: 10.1007/s00018-023-05041-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2023] [Revised: 10/13/2023] [Accepted: 11/06/2023] [Indexed: 12/17/2023]
Abstract
Cystatin F, a cysteine peptidase inhibitor, is a potent modulator of NK cytotoxicity. By inhibiting granule-mediated cytotoxicity pathway, cystatin F induces formation of non-functional NK cell stage, called split-anergy. We show that N-glycosylation determines the localization and cellular function of cystatin F. Cystatin F mostly exhibited high-mannose glycosylation in U-937 cells, both high-mannose and complex glycosylation in NK-92 and primary NKs, and predominantly complex glycosylation in super-charged NKs. Manipulating N-glycosylation with kifunensine increased high-mannose glycosylation of cystatin F and lysosome localisation, which decreased cathepsin C activity and reduced NK cytotoxicity. Mannose-6-phosphate could significantly reduce the internalization of extracellular cystatin F. By comparing NK cells with different cytotoxic potentials, we found that high-mannose cystatin F was strongly associated with lysosomes and cathepsin C in NK-92 cell line. In contrast, in highly cytotoxic super-charged NKs, cystatin F with complex glycosylation was associated with the secretory pathway and less prone to inhibit cathepsin C. Modulating glycosylation to alter cystatin F localisation could increase the cytotoxicity of NK cells, thereby enhancing their therapeutic potential for treating cancer patients.
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Affiliation(s)
- Emanuela Senjor
- Department of Biotechnology, Jožef Stefan Institute, Ljubljana, Slovenia
- Faculty of Pharmacy, University of Ljubljana, Aškerčeva Cesta 7, 1000, Ljubljana, Slovenia
| | - Martina Pirro
- Center for Proteomics and Metabolomics, Leiden University Medical Center, Leiden, The Netherlands
| | - Urban Švajger
- Faculty of Pharmacy, University of Ljubljana, Aškerčeva Cesta 7, 1000, Ljubljana, Slovenia
- Blood Transfusion Centre of Slovenia, Ljubljana, Slovenia
| | - Mateja Prunk
- Department of Biotechnology, Jožef Stefan Institute, Ljubljana, Slovenia
| | - Jerica Sabotič
- Department of Biotechnology, Jožef Stefan Institute, Ljubljana, Slovenia
| | - Anahid Jewett
- Division of Oral Biology and Medicine, The Jane and Jerry Weintraub Center for Reconstructive Biotechnology, School of Dentistry, University of California Los Angeles, Los Angeles, USA
- The Jonsson Comprehensive Cancer Center, Los Angeles, USA
| | - Paul J Hensbergen
- Center for Proteomics and Metabolomics, Leiden University Medical Center, Leiden, The Netherlands
| | | | - Janko Kos
- Department of Biotechnology, Jožef Stefan Institute, Ljubljana, Slovenia.
- Faculty of Pharmacy, University of Ljubljana, Aškerčeva Cesta 7, 1000, Ljubljana, Slovenia.
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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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Abstract
A hallmark of eukaryotic cells is the ability to form a secretory pathway connecting many intracellular compartments. In the early secretory pathway, coated protein complex II (COPII)-coated vesicles mediate the anterograde transport of newly synthesized secretory cargo from the endoplasmic reticulum to the Golgi apparatus. The COPII coat complex is comprised of an inner layer of Sec23/Sec24 heterodimers and an outer layer of Sec13/Sec31 heterotetramers. In African trypanosomes, there are two paralogues each of Sec23 and Sec24, that form obligate heterodimers (TbSec23.2/TbSec24.1, TbSec23.1/TbSec24.2). It is not known if these form distinct homotypic classes of vesicles or one heterotypic class, but it is known that TbSec23.2/TbSec24.1 specifically mediate forward trafficking of GPI-anchored proteins (GPI-APs) in bloodstream-form trypanosomes (BSF). Here, we showed that this selectivity was lost in insect procyclic stage parasites (PCF). All isoforms of TbSec23 and TbSec24 are essential in PCF parasites as judged by RNAi knockdowns. RNAi silencing of each subunit had equivalent effects on the trafficking of GPI-APs and p67, a transmembrane lysosomal protein. However, silencing of the TbSec23.2/TbSec24.1 had heterodimer had a significant impact on COPII mediated trafficking of soluble TbCatL from the ER to the lysosome. This finding suggests a model in which selectivity of COPII transport was altered between the BSF and PCF trypanosomes, possibly as an adaptation to a digenetic life cycle. IMPORTANCE African trypanosomes synthesize dense surface coats composed of stage-specific glycosylphosphatidylinositol lipid anchored proteins. We previously defined specific machinery in bloodstream stage parasites that mediate the exit of these proteins from the endoplasmic reticulum. Here, we performed similar analyses in the procyclic insect stage and found significant differences in this process. These findings contribute to our understanding of secretory processes in this unusual eukaryotic model system.
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Turnover of Variant Surface Glycoprotein in Trypanosoma brucei Is Not Altered in Response to Specific Silencing. mSphere 2022; 7:e0012222. [PMID: 35727016 PMCID: PMC9429888 DOI: 10.1128/msphere.00122-22] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
African trypanosomes evade the immune system of the mammalian host by the antigenic variation of the predominant glycosylphosphatidylinositol (GPI)-anchored surface protein, variant surface glycoprotein (VSG). VSG is a very stable protein that is turned over from the cell surface with a long half-life (~26 h), allowing newly synthesized VSG to populate the surface. We have recently demonstrated that VSG turnover under normal growth is mediated by a combination of GPI hydrolysis and direct shedding with intact GPI anchors. VSG synthesis is tightly regulated in dividing trypanosomes, and when subjected to RNA interference (RNAi) silencing, cells display rapid cell cycle arrest in order to conserve VSG density on the cell surface (K. Sheader, S. Vaughan, J. Minchin, K. Hughes, et al., Proc Natl Acad Sci U S A 102:8716-8721, 2005, https://doi.org/10.1073/pnas.0501886102). Arrested cells also display an altered morphology of secretory organelles-engorgement of the trans-Golgi cisternae-that may reflect a disruption of post-Golgi secretory transport. We now ask whether trypanosomes under VSG silencing also reduce the rate of VSG turnover to further conserve coat density. Our data indicate that trypanosomes do not regulate VSG turnover according to VSG protein abundance, nor was there any effect on the post-Golgi transport of soluble or GPI-anchored secretory cargo. However, the surface morphology of silenced cells was altered from a typically rugose topology to a smoother profile, consistent with reduced overall membrane trafficking to the cell surface. IMPORTANCE African trypanosomes evade the host immune system by altering the expression of variant surface glycoproteins (VSGs) in a process called antigenic variation. VSG is essential, and when its synthesis is ablated by RNAi silencing, cells enter precytokinesis growth arrest as a means to maintain constant cell surface VSG levels. We have investigated whether arrested cells also alter the rate of natural VSG turnover as a means to conserve the surface coat. This work provides insights into the natural biology of the glycocalyx of this important human and veterinary parasite.
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Kabiri M, Steverding D. Trypanosoma brucei transferrin receptor: Functional replacement of the GPI anchor with a transmembrane domain. Mol Biochem Parasitol 2021; 242:111361. [PMID: 33450336 DOI: 10.1016/j.molbiopara.2021.111361] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2020] [Revised: 01/05/2021] [Accepted: 01/08/2021] [Indexed: 10/22/2022]
Abstract
The transferrin receptor of Trypanosoma brucei (TbTfR) is a heterodimer of a glycosylphosphatidylinositol (GPI)-anchored ESAG6 subunit and an ESAG7 subunit. To investigate whether the GPI-anchor is essential for the function of the TbTfR, an ESAG6 with a transmembrane domain instead of a GPI-anchor (ESAG6tmd) was inducibly expressed in bloodstream form trypanosomes. It is shown that the ESAG6tmd is able to dimerise with ESAG7 to form a TbTfR that can bind transferrin. Fractionation experiments clearly demonstrated that the transmembrane-anchored TbTfR is exclusively associated with the membrane fraction. No difference in the uptake of transferrin was observed between trypanosomes inducibly expressing a transmembrane-anchored TbTfR and trypanosomes inducibly expressing a GPI-anchored TbTfR. Differences in glycosylation pattern of ESAG6tmd and native ESAG6 may indicate different intracellular trafficking of transmembrane- and GPI-anchored TbTfRs. The findings suggest that the GPI-anchor is not essential for the function of the TbTfR in bloodstream forms of T. brucei.
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Affiliation(s)
- Mostafa Kabiri
- Abteilung Parasitologie, Hygiene-Institut der Ruprecht-Karls Universität, Heidelberg, Germany; Sanofi Aventis Deutschland, Translational in Vivo Models, Sanofi Research and Development, Frankfurt, Germany
| | - Dietmar Steverding
- Abteilung Parasitologie, Hygiene-Institut der Ruprecht-Karls Universität, Heidelberg, Germany; Bob Champion Research and Education Centre, Norwich Medical School, University of East Anglia, Norwich, United Kingdom.
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