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Huang C, Suzuki T. The occurrence of nonglycosylated forms of
N
‐glycoprotein upon proteasome inhibition does not confirm cytosolic deglycosylation. FEBS Lett 2020; 594:1433-1442. [DOI: 10.1002/1873-3468.13734] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2019] [Revised: 12/20/2019] [Accepted: 01/06/2020] [Indexed: 11/07/2022]
Affiliation(s)
- Chengcheng Huang
- Glycometabolic Biochemistry Laboratory RIKEN Cluster for Pioneering Research Wako Japan
| | - Tadashi Suzuki
- Glycometabolic Biochemistry Laboratory RIKEN Cluster for Pioneering Research Wako Japan
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2
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Harada Y, Hirayama H, Suzuki T. Generation and degradation of free asparagine-linked glycans. Cell Mol Life Sci 2015; 72:2509-33. [PMID: 25772500 PMCID: PMC11113800 DOI: 10.1007/s00018-015-1881-7] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2014] [Revised: 02/19/2015] [Accepted: 03/05/2015] [Indexed: 10/23/2022]
Abstract
Asparagine (N)-linked protein glycosylation, which takes place in the eukaryotic endoplasmic reticulum (ER), is important for protein folding, quality control and the intracellular trafficking of secretory and membrane proteins. It is known that, during N-glycosylation, considerable amounts of lipid-linked oligosaccharides (LLOs), the glycan donor substrates for N-glycosylation, are hydrolyzed to form free N-glycans (FNGs) by unidentified mechanisms. FNGs are also generated in the cytosol by the enzymatic deglycosylation of misfolded glycoproteins during ER-associated degradation. FNGs derived from LLOs and misfolded glycoproteins are eventually merged into one pool in the cytosol and the various glycan structures are processed to a near homogenous glycoform. This article summarizes the current state of our knowledge concerning the formation and catabolism of FNGs.
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Affiliation(s)
- Yoichiro Harada
- Glycometabolome Team, Systems Glycobiology Research Group, RIKEN-Max Planck Joint Research Center, Global Research Cluster, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 Japan
| | - Hiroto Hirayama
- Glycometabolome Team, Systems Glycobiology Research Group, RIKEN-Max Planck Joint Research Center, Global Research Cluster, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 Japan
| | - Tadashi Suzuki
- Glycometabolome Team, Systems Glycobiology Research Group, RIKEN-Max Planck Joint Research Center, Global Research Cluster, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 Japan
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3
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Alonzi DS, Kukushkin NV, Allman SA, Hakki Z, Williams SJ, Pierce L, Dwek RA, Butters TD. Glycoprotein misfolding in the endoplasmic reticulum: identification of released oligosaccharides reveals a second ER-associated degradation pathway for Golgi-retrieved proteins. Cell Mol Life Sci 2013; 70:2799-814. [PMID: 23503623 PMCID: PMC11113499 DOI: 10.1007/s00018-013-1304-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2012] [Revised: 01/31/2013] [Accepted: 02/18/2013] [Indexed: 10/27/2022]
Abstract
Endoplasmic reticulum-associated degradation (ERAD) is a key cellular process whereby misfolded proteins are removed from the endoplasmic reticulum (ER) for subsequent degradation by the ubiquitin/proteasome system. In the present work, analysis of the released, free oligosaccharides (FOS) derived from all glycoproteins undergoing ERAD, has allowed a global estimation of the mechanisms of this pathway rather than following model proteins through degradative routes. Examining the FOS produced in endomannosidase-compromised cells following α-glucosidase inhibition has revealed a mechanism for clearing Golgi-retrieved glycoproteins that have failed to enter the ER quality control cycle. The Glc3Man7GlcNAc2 FOS species has been shown to be produced in the ER lumen by a mechanism involving a peptide: N-glycanase-like activity, and its production was sensitive to disruption of Golgi-ER trafficking. The detection of this oligosaccharide was unaffected by the overexpression of EDEM1 or cytosolic mannosidase, both of which increased the production of previously characterised cytosolically localised FOS. The lumenal FOS identified are therefore distinct in their production and regulation compared to FOS produced by the conventional route of misfolded glycoproteins directly removed from the ER. The production of such lumenal FOS is indicative of a novel degradative route for cellular glycoproteins that may exist under certain conditions.
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Affiliation(s)
- Dominic S. Alonzi
- Department of Biochemistry, Oxford Glycobiology Institute, University of Oxford, South Parks Road, Oxford, OX1 3QU UK
| | - Nikolay V. Kukushkin
- Department of Biochemistry, Oxford Glycobiology Institute, University of Oxford, South Parks Road, Oxford, OX1 3QU UK
| | - Sarah A. Allman
- Department of Biochemistry, Oxford Glycobiology Institute, University of Oxford, South Parks Road, Oxford, OX1 3QU UK
| | - Zalihe Hakki
- School of Chemistry and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, 30 Flemington Road, Parkville, VIC 3010 Australia
| | - Spencer J. Williams
- School of Chemistry and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, 30 Flemington Road, Parkville, VIC 3010 Australia
| | - Lorna Pierce
- Department of Biochemistry, Oxford Glycobiology Institute, University of Oxford, South Parks Road, Oxford, OX1 3QU UK
| | - Raymond A. Dwek
- Department of Biochemistry, Oxford Glycobiology Institute, University of Oxford, South Parks Road, Oxford, OX1 3QU UK
| | - Terry D. Butters
- Department of Biochemistry, Oxford Glycobiology Institute, University of Oxford, South Parks Road, Oxford, OX1 3QU UK
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4
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Sharma V, Freeze HH. Mannose efflux from the cells: a potential source of mannose in blood. J Biol Chem 2011; 286:10193-200. [PMID: 21273394 PMCID: PMC3060472 DOI: 10.1074/jbc.m110.194241] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2010] [Revised: 01/25/2011] [Indexed: 11/06/2022] Open
Abstract
All mammals have 50-100 μM mannose in their blood. However, the source of the dynamic pool of mannose in blood is unknown. Most of it is thought to be derived from glucose in the cells. We studied mannose uptake and release by various cell types. Interestingly, our results show that mannose taken up by the cells through transporters is handled differently from the mannose released within the cells due to glycan processing of protein-bound oligosaccharides. Although more than 95% of incoming mannose is catabolized, most of the mannose released by intracellular processing is expelled from the cells as free mannose predominantly via a nocodazole-sensitive sugar transporter. Under physiological conditions, incoming mannose is more accessible to hexokinase, whereas mannose released within the cells is protected from HK and therefore has a different fate. Our data also suggest that generation of free mannose due to the processing of glycoconjugates composed of glucose-derived mannose and its efflux from the cells can account for most of the mannose found in blood and its steady state maintenance.
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Affiliation(s)
- Vandana Sharma
- Sanford Children's Health Research Center, Sanford-Burnham Medical Research Institute, La Jolla, California 92037, USA
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Laroche-Pierre S, Jodoin J, LeBlanc AC. Helix 3 is necessary and sufficient for prion protein's anti-Bax function. J Neurochem 2009; 108:1019-31. [PMID: 19196429 DOI: 10.1111/j.1471-4159.2008.05851.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
To identify the structural elements of the prion protein (PrP) necessary for its protective function against Bcl-2 associated protein X (Bax), we performed structure-function analyses of the anti-Bax function of cytosolic PrP (CyPrP) in MCF-7 cells. Deletions of 1, 2, or 3 N-terminal Bcl-2 homology domain 2-like octapeptide repeats (BORs), but not deletion of all four BORs, abolish CyPrPs anti-Bax function. Deletion of alpha-helix 3 (PrP23-199) or further C-terminal deletions of alpha-helix 1 and 2, and beta-strand 1 and 2 (PrP23-172, PrP23-160, PrP23-143, and PrP23-127) eliminates CyPrPs protection against Bax-mediated cell death. The substitution of helix 3 amino acid residues K204, V210, and E219 by proline inhibits the anti-Bax function of CyPrP. The substitution of K204, but not V210 and E219, by alanine residues also prevents CyPrPs anti-Bax function. Expression of PrPs helix 3 displays anti-Bax activity in MCF-7 cells and in human neurons. Together, these results indicate that although the BOR domain has an influence on PrPs anti-Bax function, the helix 3 is necessary and sufficient for the anti-Bax function of CyPrP. Identification of helix 3 as the structural element for the anti-Bax function thus provides a molecular target to modulate PrPs anti-Bax function in cancer and neurodegeneration.
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Affiliation(s)
- Stéphanie Laroche-Pierre
- Bloomfield Center for Research in Aging, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital, Montréal, Quebec, Canada
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Funakoshi Y, Suzuki T. Glycobiology in the cytosol: the bitter side of a sweet world. Biochim Biophys Acta Gen Subj 2008; 1790:81-94. [PMID: 18952151 DOI: 10.1016/j.bbagen.2008.09.009] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2008] [Revised: 08/03/2008] [Accepted: 09/11/2008] [Indexed: 01/11/2023]
Abstract
Progress in glycobiology has undergone explosive growth over the past decade with more of the researchers now realizing the importance of glycan chains in various inter- and intracellular processes. However, there is still an area of glycobiology awaiting exploration. This is especially the case for the field of "glycobiology in the cytosol" which remains rather poorly understood. Yet evidence is accumulating to demonstrate that the glycoconjugates and their recognition molecules (i.e. lectins) are often present in this subcellular compartment.
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Affiliation(s)
- Yoko Funakoshi
- Glycometabolome Team, Systems Glycobiology Research Group, RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako Saitama, 351-0198, Japan
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Suzuki T, Funakoshi Y. Free N-linked oligosaccharide chains: formation and degradation. Glycoconj J 2007; 23:291-302. [PMID: 16897173 DOI: 10.1007/s10719-006-6975-x] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2005] [Revised: 12/21/2005] [Accepted: 12/27/2005] [Indexed: 01/09/2023]
Abstract
There is growing evidence that N-linked glycans play pivotal roles in protein folding and intra- and/or intercellular trafficking of N-glycosylated proteins. It has been shown that during the N-glycosylation of proteins, significant amounts of free oligosaccharides (free OSs) are generated in the lumen of the endoplasmic reticulum (ER) by a mechanism which remains to be clarified. Free OSs are also formed in the cytosol by enzymatic deglycosylation of misfolded glycoproteins, which are subjected to destruction by a cellular system called "ER-associated degradation (ERAD)." While the precise functions of free OSs remain obscure, biochemical studies have revealed that a novel cellular process enables them to be catabolized in a specialized manner, that involves pumping free OSs in the lumen of the ER into the cytosol where further processing occurs. This process is followed by entry into the lysosomes. In this review we summarize current knowledge about the formation, processing and degradation of free OSs in eukaryotes and also discuss the potential biological significance of this pathway. Other evidence for the occurrence of free OSs in various cellular processes is also presented.
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Affiliation(s)
- Tadashi Suzuki
- 21st COE (Center of Excellence) Program and Department of Biochemistry, Osaka University Graduate School of Medicine, Suita, Osaka 565-0871, Japan.
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Sriram V, Willard CA, Liu J, Brutkiewicz RR. Importance of N-linked glycosylation in the functional expression of murine CD1d1. Immunology 2007; 123:272-81. [PMID: 17725604 PMCID: PMC2433293 DOI: 10.1111/j.1365-2567.2007.02696.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
The mouse CD1d1 glycoprotein is specialized in presenting lipid antigens to a novel class of T cells called natural killer T (NKT) cells. CD1d1 is predicted to contain five potential N-linked glycosylation sites (asparagine residues at positions 25, 38, 60, 128, and 183). Glycosylation has been shown to invariably affect the molecular and functional properties of various glycoproteins, and in the current report it was found that a conservative change of the individual endogenous asparagine residues in CD1d1 to glutamine differentially affected its functional expression. Although the maturation rate of the glycosylation mutants was comparable to that of wild type, they differed in their relative levels of surface expression and in their ability to stimulate NKT cells. Mutating all five glycosylation residues resulted in the absence of detectable CD1d1 expression, with a concomitant lack of NKT cell activation. Therefore, these results demonstrate that glycosylation plays a significant role in the functional expression of CD1d1.
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Affiliation(s)
- Venkataraman Sriram
- Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis, IN 46202, USA
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Lederkremer GZ, Glickman MH. A window of opportunity: timing protein degradation by trimming of sugars and ubiquitins. Trends Biochem Sci 2005; 30:297-303. [PMID: 15950873 DOI: 10.1016/j.tibs.2005.04.010] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2005] [Revised: 03/14/2005] [Accepted: 04/25/2005] [Indexed: 11/15/2022]
Abstract
Of the many post-translational modifications of proteins, ubiquitination and N-glycosylation stand out because they are polymeric additions. In contrast to single-unit modifications, the fate of the modified protein is determined by the dynamic equilibrium of polymerization versus depolymerization, rather than by the initial addition itself. Notably, it is the trimming of sugar chains and elongation of polyubiquitin that target the protein to degradation. Recent research suggests that, for each process, special receptors recognize chains that reach an appropriate length and commit the conjugated substrate for proteasomal disposal. We propose that the 'magic numbers' are loss of at least three mannose residues from the initial chain, or extension to at least four ubiquitins. Although these processes are compartmentalized to either side of the endoplasmic reticulum (ER) membrane, some proteins are sequentially subjected to both because they transverse this membrane for ER-associated degradation.
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Affiliation(s)
- Gerardo Z Lederkremer
- Department of Cell Research and Immunology, George Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
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Ihara Y, Kageyama K, Kondo T. Overexpression of calreticulin sensitizes SERCA2a to oxidative stress. Biochem Biophys Res Commun 2005; 329:1343-9. [PMID: 15766574 DOI: 10.1016/j.bbrc.2005.02.112] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2005] [Indexed: 11/19/2022]
Abstract
Calreticulin (CRT), a Ca(2+)-binding molecular chaperone in the endoplasmic reticulum, plays a vital role in cardiac physiology and pathology. Oxidative stress is a main cause of myocardiac disorder in the ischemic heart, but the function of CRT under oxidative stress is not fully understood. In this study, the effect of overexpression of CRT on sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase (SERCA) 2a under oxidative stress was examined using myocardiac H9c2 cells transfected with the CRT gene. The in vitro activity of SERCA2a and uptake of (45)Ca(2+) into isolated microsomes were suppressed by H(2)O(2) in CRT-overexpressing cells compared with controls. Moreover, SERCA2a protein was degraded via a proteasome-dependent pathway following the formation of a complex with CRT under the stress with H(2)O(2). Thus, we conclude that overexpression of CRT enhances the inactivation and degradation of SERCA2a in the cells under oxidative stress, suggesting some pathophysiological functions of CRT in Ca(2+) homeostasis of myocardiac disease.
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Affiliation(s)
- Yoshito Ihara
- Department of Biochemistry and Molecular Biology in Disease, Atomic Bomb Disease Institute, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki 852-8523, Japan.
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11
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Kitzmüller C, Caprini A, Moore SEH, Frénoy JP, Schwaiger E, Kellermann O, Ivessa NE, Ermonval M. Processing of N-linked glycans during endoplasmic-reticulum-associated degradation of a short-lived variant of ribophorin I. Biochem J 2003; 376:687-96. [PMID: 12952521 PMCID: PMC1223801 DOI: 10.1042/bj20030887] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2003] [Revised: 08/01/2003] [Accepted: 09/03/2003] [Indexed: 11/17/2022]
Abstract
Recently, the role of N-linked glycans in the process of ERAD (endoplasmic reticulum-associated degradation) of proteins has been widely recognized. In the present study, we attempted to delineate further the sequence of events leading from a fully glycosylated soluble protein to its deglycosylated form. Degradation intermediates of a truncated form of ribophorin I, namely RI(332), which contains a single N-linked oligosaccharide and is a substrate for the ERAD/ubiquitin-proteasome pathway, were characterized in HeLa cells under conditions blocking proteasomal degradation. The action of a deoxymannojirimycin- and kifunensine-sensitive alpha1,2-mannosidase was shown here to be required for both further glycan processing and progression of RI(332) in the ERAD pathway. In a first step, the Man(8) isomer B, generated by ER mannosidase I, appears to be the major oligomannoside structure associated with RI(332) intermediates. Some other trimmed N-glycan species, in particular Glc(1)Man(7)GlcNAc(2), were also found on the protein, indicating that several mannosidases might be implicated in the initial trimming of the oligomannoside. Secondly, another intermediate of degradation of RI(332) accumulated after proteasome inhibition. We demonstrated that this completely deglycosylated form arose from the action of an N-glycanase closely linked to the ER membrane. Indeed, the deglycosylated form of the protein remained membrane-associated, while being accessible from the cytoplasm to ubiquitinating enzymes and to added protease. Our results indicate that deglycosylation of a soluble ERAD substrate glycoprotein occurs in at least two distinct steps and is coupled with the retro-translocation of the protein preceding its proteasomal degradation.
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Affiliation(s)
- Claudia Kitzmüller
- Max F. Perutz Laboratories, University Departments at the Vienna Biocenter and Institute of Medical Biochemistry, Department of Molecular Genetics, University of Vienna, Austria
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Abstract
Successful maturation determines the intracellular fate of secretory and membrane proteins in the endoplasmic reticulum (ER). Failure of proteins to fold or assemble properly can lead to their retention in the ER and redirects them to the cytosol for degradation by the proteasome. Proteasome inhibitors can yield deglycosylated cytoplasmic intermediates that are the result of an N-glycanase activity, believed to act prior to destruction of these substrates by the proteasome. A gene encoding a yeast peptide:N-glycanase, PNG1, has been cloned, but this N-glycanase and its mammalian homolog were reported to be incapable of deglycosylating full-length glycoproteins. We show that both the yeast PNG1 enzyme and its mammalian homolog display N-glycanase activity towards intact glycoproteins. As substrates, cytosolic PNGase activity prefers proteins containing high-mannose over those bearing complex type oligosaccharides. Importantly, PNG1 discriminates between non-native and folded glycoproteins, consistent with a role for N-glycanase in cytoplasmic turnover of glycoproteins.
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Affiliation(s)
| | | | - Hidde L. Ploegh
- Department of Pathology, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA
Corresponding author e-mail:
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Suzuki T, Lennarz WJ. Glycopeptide export from the endoplasmic reticulum into cytosol is mediated by a mechanism distinct from that for export of misfolded glycoprotein. Glycobiology 2002; 12:803-11. [PMID: 12499402 DOI: 10.1093/glycob/cwf095] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
When glycoproteins formed in the endoplasmic reticulum (ER) are misfolded, they are generally translocated into the cytosol for ubiquitination and are subsequently degraded by the proteasome. This system, the so-called ER-associated glycoprotein degradation, is important for eukaryotes to maintain the quality of glycoproteins generated in the ER. It has been established in yeast that several distinct proteins are involved in this translocation and degradation processes. Small glycopeptides formed in the ER are exported to the cytosol in a similar manner. This glycopeptide export system is conserved from yeast to mammalian cells, suggesting its basic biological significance for eukaryotic cells. These two export systems (for misfolded glycoproteins and glycopeptides) share some properties, such as a requirement for ATP and involvement of Sec61p, a central membrane protein presumably forming a dislocon channel for export of proteins. However, the machinery of glycopeptide export is poorly understood. In this study, various mutants known to have an effect on export/degradation of misfolded glycoproteins were examined for glycopeptide export activity with a newly established assay method. Surprisingly, most of the mutants were found not to exhibit a defect in glycopeptide export. The only gene that was found to be required on efficient export of both types of substrates was PMR1, the gene encoding the medial-Golgi Ca(2+)/Mn(2+)-ion pump. These results provide evidence that although the systems involved in export of misfolded glycoproteins and glycopeptides share some properties, they have exhibited distinct differences.
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Affiliation(s)
- Tadashi Suzuki
- Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo and PRESTO, Japan Science and Technology Corporation (JST), Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan
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Kimura Y, Matsuo S, Tsurusaki S, Kimura M, Hara-Nishimura I, Nishimura M. Subcellular localization of endo-beta-N-acetylglucosaminidase and high-mannose type free N-glycans in plant cell. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1570:38-46. [PMID: 11960687 DOI: 10.1016/s0304-4165(02)00149-6] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Subcellular distribution of plant endo-beta-N-acetylglucosaminidase (endo-beta-GlcNAc-ase) and high-mannose type free N-glycans produced by the endoglycosidase has been analyzed using cotyledons of pumpkin seedlings as the model plant cells. Each organelle in the cotyledons was fractionated by ultracentrifugation with the sucrose density gradient system and the endo-beta-GlcNAc-ase activity in each fraction was assayed with fluorescence labeled N-glycans as substrates. The endoglycosidase activity was exclusively recovered in the soluble fraction (cytosol fraction) but not in other specific organellar fractions, suggesting that the endoglycosidase would reside predominantly in the cytosol. The quantitative analysis of high-mannose type free N-glycans occurring in each fraction showed that more than 70% of the free N-glycans was recovered from the soluble fraction, suggesting the endoglycosidase would work in the cytosol and the resulting free N-glycans would accumulate in the same fraction. The pumpkin endo-beta-GlcNAc-ase (endo-CM) partially purified from the cotyledons showed optimum activity around pH 6.5, supporting this enzyme would reside in the cytosol. Furthermore, the detailed analysis of substrate specificity of endo-CM using various high-mannose type N-glycans showed that the pumpkin enzyme, as well as other plant endo-beta-N-acetylglucosaminidases, were highly active toward the high-mannose type glycans bearing the Man(alpha1)-2Man(alpha1)-3Man(beta1)-structural unit.
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Affiliation(s)
- Yoshinobu Kimura
- Department of Bioresources Chemistry, Faculty of Agriculture, Okayama University, 700-8530, Okayama, Japan.
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Petzelt C, Joswig G, Stammer H, Werner D. Cytotoxic cyplasin of the sea hare, Aaplysia punctata, cDNA cloning, and expression of bioactive recombinants in insect cells. Neoplasia 2002; 4:49-59. [PMID: 11922391 PMCID: PMC1503318 DOI: 10.1038/sj.neo.7900202] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A 56-kDa protein isolated from the mucus of the European sea hare Aplysia punctata shows a prefer ential toxicity to autonomously growing transformed mammalian cells. Cell death induced by this protein differs from both apoptosis and necrosis. The cytotoxic effects are irreversible and become apparent at nanomolar concentrations in a cell type-dependent manner. In contrast, injection of micromolar concentrations into mice is tolerated without apparent negative consequences. Microsequencing of the 56-kDa protein released a peptide sequence whose corresponding nucleotide sequence was used as probe to screen A. punctata RNA-based cDNA and to select cDNA clones encoding polypeptides comprising the target peptide. Two closely related cDNA were detected. The cDNA encoding a polypeptide 558 aa in length was considered to reflect a bonafide clone encoding the cytotoxic protein. Its protein-coding section was recloned in vectors suitable for expression in Escherichia coli, in mammalian cells, and in insect cells, respectively. The E. coli-expressed polypeptide was biologically inactive. Transfected mammalian cells expressed a cytotoxic factor and died thereof as if treated with the genuine cytotoxic protein. In contrast, transfected insect cells, which proved to be much less sensitive when treated with the genuine protein, expressed the cytotoxic factor and continued to proliferate, allowing to establish stable insect cell lines expressing sufficient amounts of the cytotoxic factor for further characterization.
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Spiro MJ, Spiro RG. Release of polymannose oligosaccharides from vesicular stomatitis virus G protein during endoplasmic reticulum-associated degradation. Glycobiology 2001; 11:803-11. [PMID: 11588156 DOI: 10.1093/glycob/11.10.803] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
To further explore the localization of the N-deglycosylation involved in the endoplasmic reticulum (ER)-associated quality control system we studied HepG2 cells infected with vesicular stomatitis virus (VSV) and its ts045 mutant, as in this system oligosaccharide release can be attributed solely to the VSV glycoprotein (G protein). We utilized the restricted intracellular migration of the mutant protein as well as dithiothreitol (DTT), low temperature, and a castanospermine (CST)-imposed glucosidase blockade to determine in which intracellular compartment deglycosylation takes place. Degradation of the VSV ts045 G protein was considerably greater at the nonpermissive than at the permissive temperature; this was reflected by a substantial increase in polymannose oligosaccharide release. Under both conditions these oligosaccharides were predominantly in the characteristic cytosolic form, which terminates in a single N-acetylglucosamine (OS-GlcNAc(1)); this was also the case in the presence of DTT, which retains the G protein completely in the ER. However when cells infected with the VSV mutant were examined at 15 degrees C or exposed to CST, both of which represent conditions that impair ER-to-cytosol transport, the released oligosaccharides were almost exclusively (> 95%) in the vesicular OS-GlcNAc(2) form; glucosidase blockade had a similar effect on the wild-type virus. Addition of puromycin to glucosidase-inhibited cells resulted in a pronounced reduction (> 90%) in oligosaccharide release, which reflected a comparable impairment in glycoprotein biosynthesis and indicated that the OS-GlcNAc(2) components originated from protein degradation rather than hydrolysis of oligosaccharide lipids. Our findings are consistent with N-deglycosylation of the VSV G protein in the ER and the subsequent transport of the released oligosaccharides to the cytosol where OS-GlcNAc(2) to OS-GlcNAc(1) conversion by an endo-beta-N-acetylglucosaminidase takes place. Studies with the ts045 G protein at the nonpermissive temperature permitted us to determine that it can be processed by Golgi endomannosidase although remaining endo H sensitive, supporting the concept that it recycles between the ER and cis-Golgi compartments.
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Affiliation(s)
- M J Spiro
- Department of Medicine, Harvard Medical School, Joslin Diabetes Center, 1 Joslin Place, Boston, Massachusetts 02215, USA
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Cacan R, Duvet S, Labiau O, Verbert A, Krag SS. Monoglucosylated oligomannosides are released during the degradation process of newly synthesized glycoproteins. J Biol Chem 2001; 276:22307-12. [PMID: 11294837 DOI: 10.1074/jbc.m101077200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Chinese hamster ovary mutant MI8-5 is known to synthesize Man(9)GlcNAc(2)-P-P-dolichol rather than the fully glucosylated lipid intermediate Glc(3)Man(9)GlcNAc(2)-P-P-dolichol. This nonglucosylated oligosaccharide lipid precursor is used as donor for N-glycosylation. In this paper we demonstrate that a significant part of the glycans bound to the newly synthesized glycoproteins in MI8-5 cells are monoglucosylated. The presence of monoglucosylated glycans on glycoproteins determines their binding to calnexin as part of the quality control machinery. Furthermore, we point out the presence of Glc(1)Man(5)GlcNAc(1) in the cytosol of MI8-5 cells. This indicates that part of the monoglucosylated glycoproteins can be directed toward a deglycosylation process that occurs in the cytosol. Besides studies on glycoprotein degradation based on the disappearance of protein moieties, MI8-5 cells can be used as a tool to elucidate the various step leading to glycoprotein degradation by studying the fate of the glycan moieties.
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Affiliation(s)
- R Cacan
- Laboratoire de Chimie Biologique, CNRS-UMR 8576, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq Cedex, France.
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Rothbarth K, Kempf T, Juodka B, Glaser T, Stammer H, Werner D. Intracellular location and nuclear targeting of the Spi-1, Spi-2 and Spi-3 gene-derived serine protease inhibitors in non-secretory cells. Eur J Cell Biol 2001; 80:341-8. [PMID: 11432724 DOI: 10.1078/0171-9335-00170] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Proteases and their inhibitors are indispensable for the regulated activation and/or degradation of structural and functional proteins involved in basic cellular processes, e.g. in cell cycle control, cell growth, differentiation and apoptosis. In this context the serine protease inhibitors derived from the murine Spi-1, Spi-2 and Spi-3 genes, and their human homologs, deserve reconsideration. Microsequencing data indicate that a fraction of the three serpins has the capability to constitute a well characterized proteinase K, high salt and SDS-stable complex which coisolates with DNA under salting out conditions from various cell and tissue types. This tight association with DNA isolated under conditions designed to deproteinize DNA efficiently points to an in situ preformed chromatin complex. Accordingly, in addition to their well known functions as 'serum protease inhibitors' the Spi-1 and Spi-2 gene-derived proteins appear to have intracellular functions as well. The involvement of the three serpins in chromatin complexes requires their nuclear translocation. Application of (enhanced) green fluorescent protein technology and optical section microscopy reveals that truncation of the N-terminal signal sequences of the Spi-1 and Spi-2 gene-encoded proteins is a prerequisite for their nuclear translocation while non-truncated fusion proteins are enriched at the nuclear indentation which is the site of the Golgi apparatus and the centrosome. The identification of new species of intracellular serpins is of potential interest with respect to accumulating evidence for serine protease inhibitor-dependent inhibition or prevention of apoptosis.
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Affiliation(s)
- K Rothbarth
- Division of Biochemistry of the Cell (B0300), German Cancer Research Center, Heidelberg
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Spiro RG. Glucose residues as key determinants in the biosynthesis and quality control of glycoproteins with N-linked oligosaccharides. J Biol Chem 2000; 275:35657-60. [PMID: 11007802 DOI: 10.1074/jbc.r000022200] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Affiliation(s)
- R G Spiro
- Departments of Biological Chemistry and Medicine, Harvard Medical School and Joslin Diabetes Center, Boston, Massachusetts 02215, USA.
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