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Ness TJ, Gamage DG, Ekanayaka SA, Hendrickson TL. A Soluble, Minimalistic Glycosylphosphatidylinositol Transamidase (GPI-T) Retains Transamidation Activity. Biochemistry 2022; 61:1273-1285. [PMID: 35730892 DOI: 10.1021/acs.biochem.2c00196] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Glycosylphosphatidylinositol (GPI) anchoring of proteins is a eukaryotic, post-translational modification catalyzed by GPI transamidase (GPI-T). The Saccharomyces cerevisiae GPI-T is composed of five membrane-bound subunits: Gpi8, Gaa1, Gpi16, Gpi17, and Gab1. GPI-T has been recalcitrant to in vitro structure and function studies because of its complexity and membrane-solubility. Furthermore, a reliable, quantitative, in vitro assay for this important post-translational modification has remained elusive despite its discovery more than three decades ago.Three recent reports describe the structure of GPI-T from S. cerevisiae and humans, shedding critical light on this important enzyme and offering insight into the functions of its different subunits. Here, we present the purification and characterization of a truncated soluble GPI-T heterotrimer complex (Gpi823-306, Gaa150-343, and Gpi1620-551) without transmembrane domains. Using this simplified heterotrimer, we report the first quantitative method to measure GPI-T activity in vitro and demonstrate that this soluble, minimalistic GPI-T retains transamidase activity. These results contribute to our understanding of how this enzyme is organized and functions, and provide a method to screen potential GPI-T inhibitors.
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Affiliation(s)
- Travis J Ness
- Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States
| | - Dilani G Gamage
- Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States
| | - Sandamali A Ekanayaka
- Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States
| | - Tamara L Hendrickson
- Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, Michigan 48202, United States
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2
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Xu Y, Jia G, Li T, Zhou Z, Luo Y, Chao Y, Bao J, Su Z, Qu Q, Li D. Molecular insights into biogenesis of glycosylphosphatidylinositol anchor proteins. Nat Commun 2022; 13:2617. [PMID: 35551457 PMCID: PMC9098846 DOI: 10.1038/s41467-022-30250-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Accepted: 04/22/2022] [Indexed: 02/08/2023] Open
Abstract
Eukaryotic cells are coated with an abundance of glycosylphosphatidylinositol anchor proteins (GPI-APs) that play crucial roles in fertilization, neurogenesis, and immunity. The removal of a hydrophobic signal peptide and covalent attachment of GPI at the new carboxyl terminus are catalyzed by an endoplasmic reticulum membrane GPI transamidase complex (GPI-T) conserved among all eukaryotes. Here, we report the cryo-electron microscopy (cryo-EM) structure of the human GPI-T at a global 2.53-Å resolution, revealing an equimolar heteropentameric assembly. Structure-based mutagenesis suggests a legumain-like mechanism for the recognition and cleavage of proprotein substrates, and an endogenous GPI in the structure defines a composite cavity for the lipid substrate. This elongated active site, stemming from the membrane and spanning an additional ~22-Å space toward the catalytic dyad, is structurally suited for both substrates which feature an amphipathic pattern that matches this geometry. Our work presents an important step towards the mechanistic understanding of GPI-AP biosynthesis. GPI-T catalyzes the committed step in GPI anchor protein biogenesis. Here, Xu et al. report the cryo-EM structure of the human GPI-T, revealing critical elements within an elongated, shared active site which is topologically arranged for substrate specificity.
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Affiliation(s)
- Yidan Xu
- State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, University of CAS, Chinese Academy of Sciences (CAS), 320 Yueyang Road, 200030, Shanghai, China
| | - Guowen Jia
- State Key Laboratory of Biotherapy and Cancer Center, Department of Geriatrics and National Clinical Research Center for Geriatrics, West China Hospital, Sichuan University, 610044, Chengdu, China
| | - Tingting Li
- State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, University of CAS, Chinese Academy of Sciences (CAS), 320 Yueyang Road, 200030, Shanghai, China
| | - Zixuan Zhou
- Shanghai Stomatological Hospital, School of Stomatology, Shanghai Key Laboratory of Medical Epigenetics, International Co-laboratory of Medical Epigenetics and Metabolism (Ministry of Science and Technology), Institutes of Biomedical Sciences, Department of Systems Biology for Medicine, Fudan University, 200032, Shanghai, China
| | - Yitian Luo
- State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, University of CAS, Chinese Academy of Sciences (CAS), 320 Yueyang Road, 200030, Shanghai, China.,School of Life Science and Technology, ShanghaiTech University, 393 Middle Huaxia Road, 201210, Shanghai, China
| | - Yulin Chao
- Shanghai Stomatological Hospital, School of Stomatology, Shanghai Key Laboratory of Medical Epigenetics, International Co-laboratory of Medical Epigenetics and Metabolism (Ministry of Science and Technology), Institutes of Biomedical Sciences, Department of Systems Biology for Medicine, Fudan University, 200032, Shanghai, China
| | - Juan Bao
- State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, University of CAS, Chinese Academy of Sciences (CAS), 320 Yueyang Road, 200030, Shanghai, China
| | - Zhaoming Su
- State Key Laboratory of Biotherapy and Cancer Center, Department of Geriatrics and National Clinical Research Center for Geriatrics, West China Hospital, Sichuan University, 610044, Chengdu, China.
| | - Qianhui Qu
- Shanghai Stomatological Hospital, School of Stomatology, Shanghai Key Laboratory of Medical Epigenetics, International Co-laboratory of Medical Epigenetics and Metabolism (Ministry of Science and Technology), Institutes of Biomedical Sciences, Department of Systems Biology for Medicine, Fudan University, 200032, Shanghai, China.
| | - Dianfan Li
- State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, University of CAS, Chinese Academy of Sciences (CAS), 320 Yueyang Road, 200030, Shanghai, China.
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Golec E, Rosberg R, Zhang E, Renström E, Blom AM, King BC. A cryptic non-GPI-anchored cytosolic isoform of CD59 controls insulin exocytosis in pancreatic β-cells by interaction with SNARE proteins. FASEB J 2019; 33:12425-12434. [PMID: 31412214 DOI: 10.1096/fj.201901007r] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
CD59 is a glycosylphosphatidylinositol (GPI)-anchored cell surface inhibitor of the complement membrane attack complex (MAC). We showed previously that CD59 is highly expressed in pancreatic islets but is down-regulated in rodent models of diabetes. CD59 knockdown but not enzymatic removal of cell surface CD59 led to a loss of glucose-stimulated insulin secretion (GSIS), suggesting that an intracellular pool of CD59 is required. In this current paper, we now report that non-GPI-anchored CD59 is present in the cytoplasm, colocalizes with exocytotic protein vesicle-associated membrane protein 2, and completely rescues GSIS in cells lacking endogenous CD59 expression. The involvement of cytosolic non-GPI-anchored CD59 in GSIS is supported in phosphatidylinositol glycan class A knockout GPI anchor-deficient β-cells, in which GSIS is still CD59 dependent. Furthermore, site-directed mutagenesis demonstrated different structural requirements of CD59 for its 2 functions, MAC inhibition and GSIS. Our results suggest that CD59 is retrotranslocated from the endoplasmic reticulum to the cytosol, a process mediated by recognition of trimmed N-linked oligosaccharides, supported by the partial glycosylation of non-GPI-anchored cytosolic CD59 as well as the failure of N-linked glycosylation site mutant CD59 to reach the cytosol or rescue GSIS. This study thus proposes the previously undescribed existence of non-GPI-anchored cytosolic CD59, which is required for insulin secretion.-Golec, E., Rosberg, R., Zhang, E., Renström, E., Blom, A. M., King, B. C. A cryptic non-GPI-anchored cytosolic isoform of CD59 controls insulin exocytosis in pancreatic β-cells by interaction with SNARE proteins.
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Affiliation(s)
- Ewelina Golec
- Section of Medical Protein Chemistry, Department of Translational Medicine, Lund University, Malmö, Sweden
| | - Rebecca Rosberg
- Section of Medical Protein Chemistry, Department of Translational Medicine, Lund University, Malmö, Sweden
| | - Enming Zhang
- Department of Clinical Sciences Malmö, Lund University Diabetes Centre, Malmö, Sweden
| | - Erik Renström
- Department of Clinical Sciences Malmö, Lund University Diabetes Centre, Malmö, Sweden
| | - Anna M Blom
- Section of Medical Protein Chemistry, Department of Translational Medicine, Lund University, Malmö, Sweden
| | - Ben C King
- Section of Medical Protein Chemistry, Department of Translational Medicine, Lund University, Malmö, Sweden
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Gamage DG, Hendrickson TL. GPI Transamidase and GPI anchored proteins: Oncogenes and biomarkers for cancer. Crit Rev Biochem Mol Biol 2013; 48:446-64. [DOI: 10.3109/10409238.2013.831024] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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Galian C, Björkholm P, Bulleid N, von Heijne G. Efficient glycosylphosphatidylinositol (GPI) modification of membrane proteins requires a C-terminal anchoring signal of marginal hydrophobicity. J Biol Chem 2012; 287:16399-409. [PMID: 22431723 PMCID: PMC3351287 DOI: 10.1074/jbc.m112.350009] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2012] [Revised: 03/16/2012] [Indexed: 11/06/2022] Open
Abstract
Many plasma membrane proteins are anchored to the membrane via a C-terminal glycosylphosphatidylinositol (GPI) moiety. The GPI anchor is attached to the protein in the endoplasmic reticulum by transamidation, a reaction in which a C-terminal GPI-attachment signal is cleaved off concomitantly with addition of the GPI moiety. GPI-attachment signals are poorly conserved on the sequence level but are all composed of a polar segment that includes the GPI-attachment site followed by a hydrophobic segment located at the very C terminus of the protein. Here, we show that efficient GPI modification requires that the hydrophobicity of the C-terminal segment is "marginal": less hydrophobic than type II transmembrane anchors and more hydrophobic than the most hydrophobic segments found in secreted proteins. We further show that the GPI-attachment signal can be modified by the transamidase irrespective of whether it is first released into the lumen of the endoplasmic reticulum or is retained in the endoplasmic reticulum membrane.
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Affiliation(s)
- Carmen Galian
- From the Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University SE-106 91 Stockholm, Sweden
| | - Patrik Björkholm
- From the Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University SE-106 91 Stockholm, Sweden
| | - Neil Bulleid
- the Institute of Molecular, Cell and Systems Biology, CMVLS, University of Glasgow, Glasgow, G12 8QQ Scotland, United Kingdom, and
| | - Gunnar von Heijne
- From the Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University SE-106 91 Stockholm, Sweden
- the Science for Life Laboratory, Stockholm University, SE-171 77 Solna, Sweden
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Xie LP, Wu YT, Dai YP, Li Q, Zhang RQ. A novel glycosylphosphatidylinositol-anchored alkaline phosphatase dwells in the hepatic duct of the pearl oyster, Pinctada fucata. MARINE BIOTECHNOLOGY (NEW YORK, N.Y.) 2007; 9:613-23. [PMID: 17624576 DOI: 10.1007/s10126-007-9015-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2007] [Revised: 04/02/2007] [Accepted: 04/03/2007] [Indexed: 05/16/2023]
Abstract
Alkaline phosphatases are ubiquitous enzymes involved in many important biological processes. Mammalian tissue-nonspecific alkaline phosphatase (TNAP) has long been thought to play an important role in bone mineralization. In this study, we identified a full-length cDNA encoding a potential alkaline phosphatse from pearl oyster Pinctada fucata by RT-PCR and RACE and designated the encoded protein as PFAP. The sequence of PFAP shares an overall similarity of 67% with that of human TNAP. Prediction and analysis of its secondary and tertiary structure revealed that the PFAP contains two mammalian-specific regions, the crown domain, involved in collagen binding, and the calcium binding domain, which hint its potential ability to participate in biomineralization. RT-PCR and in situ hybridization showed that the PFAP mRNA distributes specifically in the hepatic duct of the digestive diverticula. These findings implied its possible role in calcium absorption and transportation. In vivo, PFAP could be specifically released by phosphatidylinositol-specific phospholipase C (PIPLC), suggesting it is glycophosphatidylinositol-anchored to the plasma membrane. Therefore, a human growth hormone-PFAP fusion was constructed to locate the cleavage/attachment site. Immunofluorescent labeling and immunoblotting showed that Asn-477 is the cleavage/attachment site and the 25-residue peptide COOH-terminal to Asn-477 is removed during glycophosphatidylinositol anchoring. This research will hopefully pave the way to illustrate the role PFAP plays in calcium transportation related to pearl biomineralization.
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Affiliation(s)
- Li-Ping Xie
- Institute of Marine Biotechnology, Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing, PR China
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Zacks MA, Garg N. Recent developments in the molecular, biochemical and functional characterization of GPI8 and the GPI-anchoring mechanism [review]. Mol Membr Biol 2006; 23:209-25. [PMID: 16785205 DOI: 10.1080/09687860600601494] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Glycoconjugates are utilized by eukaryotic organisms ranging from yeast to humans for the cell surface expression of a wide variety of proteins and lipids. These glycoconjugates are expressed as enzymes or receptors and serve a diversity of functions, including cell signaling and cell survival. In parasitic protozoans, glycoconjugates play roles in infectivity, survival, virulence and immune evasion. Among the alternate glycoconjugate structures that have been identified, glycosylphosphatidylinositols (GPIs) represent a universal structure for the anchorage of proteins, lipids, and phosphosaccharides to cellular membranes. Biosynthesis of the GPI is a multi-step process that culminates in the attachment of the assembled GPI to a precursor protein. This final step in the transfer of the GPI to a protein is catalyzed by GPI8 of the putative transamidase complex (TAM). GPI8 functions dually to perform the proteolytic cleavage of the C-terminal signal sequence of the precursor protein, followed by the formation of an amide bond between the protein and the ethanolamine phosphate of the GPI. This review summarizes the current aggregate of biochemical, gene-disruption and active site mutagenesis studies, which provide evidence that GPI8 is responsible for the protein-GPI anchoring reaction. We describe recently published studies that have identified other potential components of the TAM complex and that have elucidated their likely role in protein-GPI attachment. Further, we discuss the biochemical, molecular and functional differences between protozoan and mammalian GPI8 and the protein-GPI anchoring machinery. Finally, we will present the implications of these studies for the development of anti-parasite drug therapies.
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Affiliation(s)
- Michele A Zacks
- Department of Pathology, Center for Biodefense and Emerging Infectious Diseases, University of Texas Medical Branch, Galveston, Texas 77555-1070, USA
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Hong Y, Kang JY, Kim YU, Shin DJ, Choy HE, Maeda Y, Kinoshita T. New mutant Chinese hamster ovary cell representing an unknown gene for attachment of glycosylphosphatidylinositol to proteins. Biochem Biophys Res Commun 2005; 335:1060-9. [PMID: 16102723 DOI: 10.1016/j.bbrc.2005.07.177] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2005] [Accepted: 07/25/2005] [Indexed: 10/25/2022]
Abstract
Aerolysin, a secreted bacterial toxin from Aeromonas hydrophila, binds to glycosylphosphatidylinositol (GPI)-anchored protein and kills the cells by forming pores. Both GPI and N-glycan moieties of GPI-anchored proteins are involved in efficient binding of aerolysin. We isolated various Chinese hamster ovary (CHO) mutant cells resistant to aerolysin. Among them, CHOPA41.3 mutant cells showed several-fold decreased expression of GPI-anchored proteins. After transfection of N-acetylglucosamine transferase I (GnT1) cDNA, aerolysin was efficiently bound to the cells, indicating that the resistance against aerolysin in this cells was mainly ascribed to the defect of N-glycan maturation. CHOPA41.3 cells also accumulated GPI intermediates lacking ethanolamine phosphate modification on the first mannose. After stable transfection of PIG-N cDNA encoding GPI-ethanolamine phosphate transferase1, a profile of accumulated GPI intermediates became similar to that of GPI transamidase mutant cells. It indicated, therefore, that CHOPA41.3 cells are defective in GnT1, ethanolamine phosphate modification of the first mannose, and attachment of GPI to proteins. The GPI accumulation in CHOPA41.3 cells carrying PIG-N cDNA was not normalized after transfection with cDNAs of all known components in GPI transamidase complex. Microsomes from CHOPA41.3 cells had normal GPI transamidase activity. Taken together, there is an unknown gene required for efficient attachment of GPI to proteins.
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Affiliation(s)
- Yeongjin Hong
- Genomic Research Center for Enteropathogenic Bacteria and Department of Microbiology, Chonnam National University Medical School, Gwangju, Republic of Korea.
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Dalley JA, Bulleid NJ. The endoplasmic reticulum (ER) translocon can differentiate between hydrophobic sequences allowing signals for glycosylphosphatidylinositol anchor addition to be fully translocated into the ER lumen. J Biol Chem 2003; 278:51749-57. [PMID: 14530277 DOI: 10.1074/jbc.m303978200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The signal sequence within polypeptide chains that designates whether a protein is to be anchored to the membrane by a glycosylphosphatidylinositol (GPI) anchor is characterized by a carboxyl-terminal hydrophobic domain preceded by a short hydrophilic spacer linked to the GPI anchor attachment (omega) site. The hydrophobic domain within the GPI anchor signal sequence is very similar to a transmembrane domain within a stop transfer sequence. To investigate whether the GPI anchor signal sequence is translocated across or integrated into the endoplasmic reticulum membrane we studied the translocation, GPI anchor addition, and glycosylation of different variants of a model GPI-anchored protein. Our results unequivocally demonstrated that the hydrophobic domain within a GPI signal cannot act as a transmembrane domain and is fully translocated even when followed by an authentic charged cytosolic tail sequence. However, a single amino acid change within the hydrophobic domain of the GPI-signal converts it into a transmembrane domain that is fully integrated into the endoplasmic reticulum membrane. These results demonstrated that the translocation machinery can recognize and differentiate subtle changes in hydrophobic sequence allowing either full translocation or membrane integration.
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Affiliation(s)
- Jane A Dalley
- School of Biological Sciences, 2.205 Stopford Building, University of Manchester, Manchester M13 9PT, United Kingdom
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Hong Y, Ohishi K, Kang JY, Tanaka S, Inoue N, Nishimura JI, Maeda Y, Kinoshita T. Human PIG-U and yeast Cdc91p are the fifth subunit of GPI transamidase that attaches GPI-anchors to proteins. Mol Biol Cell 2003; 14:1780-9. [PMID: 12802054 PMCID: PMC165076 DOI: 10.1091/mbc.e02-12-0794] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Many eukaryotic proteins are anchored to the cell surface via glycosylphosphatidylinositol (GPI), which is posttranslationally attached to the carboxyl-terminus by GPI transamidase. The mammalian GPI transamidase is a complex of at least four subunits, GPI8, GAA1, PIG-S, and PIG-T. Here, we report Chinese hamster ovary cells representing a new complementation group of GPI-anchored protein-deficient mutants, class U. The class U cells accumulated mature and immature GPI and did not have in vitro GPI transamidase activity. We cloned the gene responsible, termed PIG-U, that encoded a 435-amino-acid hydrophobic protein. The GPI transamidase complex affinity-purified from cells expressing epitope-tagged-GPI8 contained PIG-U and four other known components. Cells lacking PIG-U formed complexes of the four other components normally but had no ability to cleave the GPI attachment signal peptide. Saccharomyces cerevisiae Cdc91p, with 28% amino acid identity to PIG-U, partially restored GPI-anchored proteins on the surface of class U cells. PIG-U and Cdc91p have a functionally important short region with similarity to a region conserved in long-chain fatty acid elongases. Taken together, PIG-U and the yeast orthologue Cdc91p are the fifth component of GPI transamidase that may be involved in the recognition of either the GPI attachment signal or the lipid portion of GPI.
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Affiliation(s)
- Yeongjin Hong
- Department of Immunoregulation, Research Institute for Microbial Diseases, Osaka University, Japan
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Ohishi K, Nagamune K, Maeda Y, Kinoshita T. Two subunits of glycosylphosphatidylinositol transamidase, GPI8 and PIG-T, form a functionally important intermolecular disulfide bridge. J Biol Chem 2003; 278:13959-67. [PMID: 12582175 DOI: 10.1074/jbc.m300586200] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Many eukaryotic proteins are tethered to the plasma membrane via glycosylphosphatidylinositol (GPI). GPI transamidase is localized in the endoplasmic reticulum and mediates post-translational transfer of preformed GPI to proteins bearing a carboxyl-terminal GPI attachment signal. Mammalian GPI transamidase is a multimeric complex consisting of at least five subunits. Here we report that two subunits of mammalian GPI transamidase, GPI8 and PIG-T, form a functionally important disulfide bond between conserved cysteine residues. GPI8 and PIG-T mutants in which relevant cysteines were replaced with serines were unable to fully restore the surface expression of GPI-anchored proteins upon transfection into their respective mutant cells. Microsomal membranes of these transfectants had markedly decreased activities in an in vitro transamidase assay. The formation of this disulfide bond is not essential but required for full transamidase activity. Antibodies against GPI8 and PIG-T revealed that endogenous as well as exogenous proteins formed a disulfide bond. Furthermore trypanosome GPI8 forms a similar intermolecular disulfide bond via its conserved cysteine residue, suggesting that the trypanosome GPI transamidase is also a multimeric complex likely containing the orthologue of PIG-T. We also demonstrate that an inactive human GPI transamidase complex that consists of non-functional GPI8 and four other components was co-purified with the proform of substrate proteins, indicating that these five components are sufficient to hold the substrate proteins.
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Affiliation(s)
- Kazuhito Ohishi
- Department of Immunoregulation, Research Institute for Microbial Diseases, Osaka University, Japan
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13
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Abstract
For characterizing how the glycosylphosphatidylinositol (GPI) transamidase complex functions, we exploited a two-step miniPLAP (placental alkaline phosphatase) in vitro translation system. With this system, rough microsomal membranes (RM) containing either [(35)S]-labeled Gaa1p or epitope-tagged Gpi8p, alternative components of the enzymatic complex, were first prepared. In a second translation, unmodified or mutant miniPLAP mRNA was used such that [(35)S]-labeled native or variant miniPLAP nascent protein was introduced. Following this, the RM were solubilized and anti-PLAP or anti-epitope immunoprecipitates were analyzed. With transamidase competent HeLa cell RM, anti-PLAP or anti-epitope antibody coprecipitated both Gaa1p and Gpi8p consistent with the assembly of the proprotein into a Gaa1p:Gpi8p-containing complex. When RM from K562 mutant K cells which lack Gpi8p were used, anti-PLAP antibody coprecipitated Gaa1p. The proprotein coprecipitation of Gaa1p increased with a nonpermissive GPI anchor addition (omega) site. In contrast, if a miniPLAP mutant devoid of its C-terminal signal was used, no coprecipitation occurred. During the transamidation reaction, a transient high Mr band forms. To definitively characterize this product, RM from K cells transfected with FLAG-tagged GPI8 were employed. Western blots of anti-FLAG bead isolates of solubilized RM from the cells showed that the high Mr band corresponded to Gpi8p covalently bound to miniPLAP. Loss of the band following hydrazinolysis demonstrated that the two components were associated in a thioester linkage. The data indicate that recognition of the proprotein involves Gaa1p, that the interaction with the complex does not depend on a permissive omega site, and that Gpi8p forms a thioester intermediate with the proprotein. The method could be useful for rapid analysis of nascent protein interactions with transamidase components, and possibly for helping to prepare a functional in vitro transamidase system.
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Affiliation(s)
- Rui Chen
- Institute of Pathology, Case Western Reserve University, Cleveland, Ohio 44106, USA
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Vainauskas S, Maeda Y, Kurniawan H, Kinoshita T, Menon AK. Structural requirements for the recruitment of Gaa1 into a functional glycosylphosphatidylinositol transamidase complex. J Biol Chem 2002; 277:30535-42. [PMID: 12052837 DOI: 10.1074/jbc.m205402200] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glycosylphosphatidylinositol (GPI)-anchored proteins are synthesized on membrane-bound ribosomes, translocated across the endoplasmic reticulum membrane, and GPI-anchored by GPI transamidase (GPIT). GPIT is a minimally heterotetrameric membrane protein complex composed of Gaa1, Gpi8, PIG-S and PIG-T. We describe structure-function analyses of Gaa1, the most hydrophobic of the GPIT subunits, with the aim of assigning a functional role to the different sequence domains of the protein. We generated epitope-tagged Gaa1 mutants and analyzed their membrane topology, subcellular distribution, complex-forming capability, and ability to restore GPIT activity in Gaa1-deficient cells. We show that (i) detergent-extracted, Gaa1-containing GPIT complexes sediment unexpectedly rapidly at approximately 17 S, (ii) Gaa1 is an endoplasmic reticulum-localized membrane glycoprotein with a cytoplasmically oriented N terminus and a lumenally oriented C terminus, (iii) elimination of C-terminal transmembrane segments allows Gaa1 to interact with other GPIT subunits but renders the resulting GPIT complex nonfunctional, (iv) interaction between Gaa1 and other GPIT subunits occurs via the large lumenal domain of Gaa1 located between the first and second transmembrane segments, and (v) the cytoplasmic N terminus of Gaa1 is not required for formation of a functional GPIT complex but may act as a membrane-sorting determinant directing Gaa1 and associated GPIT subunits to an endoplasmic reticulum membrane domain.
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Affiliation(s)
- Saulius Vainauskas
- Department of Biochemistry, University of Wisconsin, 433 Babcock Drive, Madison, WI 53706-1544, USA.
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Abstract
INTRODUCTION The pancreatic exocrine secretory granule, the zymogen granule, releases digestive enzymes into the intestine. GP2 is the most abundant zymogen granule membrane protein. Coincident with exocrine secretion, GP2 is released from the membrane and secreted into the pancreatic duct. AIM To characterize changes in the structure of GP2 as it progresses through the secretory pathway. METHODOLOGY Polarized MDCK cells that express the rat GP2 gene were used to examine the sequential processing of the polypeptide backbone. RESULTS Within the cell, GP2 is initially proteolytically processed from a 55- to a 53-kd form at or before the trans-Golgi network. The protein is then processed to a 51-kd form, which is found on the apical plasma membrane and in secretions. Similar processing was also observed in primary rat pancreatic cultures and in MDCK cells that express human GP2. The amino-terminal sequence of human GP2 derived from pancreatic secretions was determined for two human patients and began at Gly39, revealing a potential processing site. CONCLUSIONS In contrast to other digestive enzymes secreted by the pancreas that are activated by proteolysis in the intestine, GP2 undergoes sequential intracellular cleavage. Alterations in GP2 structure by proteolysis may regulate GP2 function at specific sites within the pancreatic cell.
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Affiliation(s)
- Benjamin A Fritz
- The Department of Medicine and Digestive Disease Center, Stanford University, Stanford, California 94305-5187, USA
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Chen R, Knez JJ, Merrick WC, Medof ME. Comparative efficiencies of C-terminal signals of native glycophosphatidylinositol (GPI)-anchored proproteins in conferring GPI-anchoring. J Cell Biochem 2002; 84:68-83. [PMID: 11746517 DOI: 10.1002/jcb.1267] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Every protein fated to receive the glycophosphatidylinositol (GPI) anchor post-translational modification has a C-terminal GPI-anchor attachment signal sequence. This signal peptide varies with respect to length, content, and hydrophobicity. With the exception of predictions based on an upstream amino acid triplet termed omega-->omega + 2 which designates the site of GPI uptake, there is no information on how the efficiencies of different native signal sequences compare in the transamidation reaction that catalyzes the substitution of the GPI anchor for the C-terminal peptide. In this study we utilized the placental alkaline phosphatase (PLAP) minigene, miniPLAP, and replaced its native 3' end-sequence encoding omega-2 to the C-terminus with the corresponding C-terminal sequences of nine other human GPI-anchored proteins. The resulting chimeras then were fed into an in vitro processing microsomal system where the cleavages leading to mature product from the nascent preproprotein could be followed by resolution on an SDS-PAGE system after immunoprecipitation. The results showed that the native signal of each protein differed markedly with respect to transamidation efficiency, with the signals of three proteins out-performing the others in GPI-anchor addition and those of two proteins being poorer substrates for the GPI transamidase. The data additionally indicated that the hierarchical order of efficiency of transamidation did not depend solely on the combination of permissible residues at omega-->omega + 2.
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Affiliation(s)
- R Chen
- Institute of Pathology, Case Western Reserve University, Cleveland, Ohio 44106, USA
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17
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Spurway TD, Dalley JA, High S, Bulleid NJ. Early events in glycosylphosphatidylinositol anchor addition. substrate proteins associate with the transamidase subunit gpi8p. J Biol Chem 2001; 276:15975-82. [PMID: 11278620 DOI: 10.1074/jbc.m010128200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The addition of glycosylphosphatidylinositol (GPI) anchors to proteins occurs by a transamidase-catalyzed reaction mechanism soon after completion of polypeptide synthesis and translocation. We show that placental alkaline phosphatase becomes efficiently GPI-anchored when translated in the presence of semipermeabilized K562 cells but is not GPI-anchored in cell lines defective in the transamidase subunit hGpi8p. By studying the synthesis of placental alkaline phosphatase, we demonstrate that folding of the protein is not influenced by the addition of a GPI anchor and conversely that GPI anchor addition does not require protein folding. These results demonstrate that folding of the ectodomain and GPI addition are two distinct processes and can be mutually exclusive. When GPI addition is prevented, either by synthesis of the protein in the presence of cell lines defective in GPI addition or by mutation of the GPI carboxyl-terminal signal sequence cleavage site, the substrate forms a prolonged association with the transamidase subunit hGpi8p. The ability of the transamidase to recognize and associate with GPI anchor signal sequences provides an explanation for the retention of GPI-anchored protein within the ER in the absence of GPI anchor addition.
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Affiliation(s)
- T D Spurway
- University of Manchester, School of Biological Sciences, 2.205 Stopford Building, Manchester M13 9PT, United Kingdom
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18
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Vidugiriene J, Vainauskas S, Johnson AE, Menon AK. Endoplasmic reticulum proteins involved in glycosylphosphatidylinositol-anchor attachment: photocrosslinking studies in a cell-free system. EUROPEAN JOURNAL OF BIOCHEMISTRY 2001; 268:2290-300. [PMID: 11298746 DOI: 10.1046/j.1432-1327.2001.02106.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Assembly of glycosylphosphatidylinositol (GPtdIns)-anchored proteins requires translocation of the nascent polypeptide chain across the endoplasmic reticulum (ER) membrane and replacement of the C-terminal signal sequence with a GPtdIns moiety. The anchoring reaction is carried out by an ER enzyme, GPtdIns transamidase. Genetic studies with yeast indicate that the transamidase consists of a dynamic complex of at least two subunits, Gaa1p and Gpi8p. To study the GPtdIns-anchoring reaction, we used a small reporter protein that becomes GPtdIns-anchored when the corresponding mRNA is translated in the presence of microsomes, in conjunction with site-specific photocrosslinking to identify ER membrane components that are proximal to the reporter during its conversion to a GPtdIns-anchored protein. We generated variants of the reporter protein such that upon in vitro translation in the presence of Nepsilon-(5-azido-2-nitrobenzoyl)-lysyl-tRNA, photoreactive lysine residues would be incorporated in the protein specifically near the GPtdIns-attachment site. We analyzed photoadducts resulting from UV irradiation of the samples. We show that proproteins can be crosslinked to the transamidase subunit Gpi8p, as well as to ER proteins of molecular mass approximately 60 kDa, approximately 70 kDa, and approximately 120 kDa. The identification of a photoadduct between a proprotein and Gpi8p provides the first direct evidence of an interaction between a proprotein substrate and one of the genetically identified transamidase subunits. The approximately 70-kDa protein that we identified may correspond to the other subunit Gaa1p, while the other proteins possibly represent additional, hitherto unidentified subunits of the mammalian GPtdIns transamidase complex.
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Affiliation(s)
- J Vidugiriene
- Department of Biochemistry, University of Wisconsin, Madison, WI 53706, USA
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19
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Ali BR, Claxton S, Field MC. Export of a misprocessed GPI-anchored protein from the endoplasmic reticulum in vitro in an ATP- and cytosol-dependent manner. FEBS Lett 2000; 483:32-6. [PMID: 11033351 DOI: 10.1016/s0014-5793(00)02073-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Strict quality control mechanisms within the mammalian endoplasmic reticulum act to prevent misfolded and unprocessed proteins from entering post-endoplasmic reticulum (ER) compartments. Following translocation into the ER lumen via the Sec61p translocon, nascent polypeptide chains fold and are modified in an environment that contains numerous chaperones and other folding mediators. Recently it has emerged that polypeptides failing to acquire the native state are re-exported from the ER to the cytosol for ultimate degradation by the proteasome ubiquitin system, apparently mediated again via Sec61p. Substrates for this degradation pathway include proteins destined to become glycosyl phosphatidylinositol (GPI)-anchored, but which fail to be processed and retain the C-terminal GPI signal peptide. In order to characterise this process we have used a model GPI-anchored mutant protein, prepro mini human placental alkaline phosphatase (PLAP) W179, which cannot be processed efficiently on account of being a poor substrate for the transamidase which cleaves the GPI signal peptide and adds the GPI anchor in a coupled reaction. In vitro transcription, translation and translocation into canine pancreatic microsomes resulted in ER-targeting signal sequence cleavage and formation of prominiPLAP in the ER lumen. We were able to show that prominiPLAPW179 could be exported from the microsomes in a time-dependent manner and that release requires both ATP and cytosol. Export was not supported by GTP, indicating a biochemical distinction from glycopeptide export which we showed recently requires GTP hydrolysis. The process was not affected by redox, unlike several other GPI-anchored model proteins. These data demonstrate that misprocessed proteins can be exported in vitro from mammalian microsomes, facilitating identification of factors involved in this process.
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Affiliation(s)
- B R Ali
- Centre for Molecular Microbiology and Infection, Wellcome Trust Laboratories for Molecular Parasitology, Department of Biochemistry, Imperial College of Science, Technology and Medicine, Exhibition Road, SW7 2AY, London, UK
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20
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Ohishi K, Inoue N, Maeda Y, Takeda J, Riezman H, Kinoshita T. Gaa1p and gpi8p are components of a glycosylphosphatidylinositol (GPI) transamidase that mediates attachment of GPI to proteins. Mol Biol Cell 2000; 11:1523-33. [PMID: 10793132 PMCID: PMC14864 DOI: 10.1091/mbc.11.5.1523] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Many eukaryotic cell surface proteins are anchored to the membrane via glycosylphosphatidylinositol (GPI). The GPI is attached to proteins that have a GPI attachment signal peptide at the carboxyl terminus. The GPI attachment signal peptide is replaced by a preassembled GPI in the endoplasmic reticulum by a transamidation reaction through the formation of a carbonyl intermediate. GPI transamidase is a key enzyme of this posttranslational modification. Here we report that Gaa1p and Gpi8p are components of a GPI transamidase. To determine a role of Gaa1p we disrupted a GAA1/GPAA1 gene in mouse F9 cells by homologous recombination. GAA1 knockout cells were defective in the formation of carbonyl intermediates between precursor proteins and transamidase as determined by an in vitro GPI-anchoring assay. We also show that cysteine and histidine residues of Gpi8p, which are conserved in members of a cysteine protease family, are essential for generation of a carbonyl intermediate. This result suggests that Gpi8p is a catalytic component that cleaves the GPI attachment signal peptide. Moreover, Gaa1p and Gpi8p are associated with each other. Therefore, Gaa1p and Gpi8p constitute a GPI transamidase and cooperate in generating a carbonyl intermediate, a prerequisite for GPI attachment.
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Affiliation(s)
- K Ohishi
- Department of Immunoregulation, Research Institute for Microbial Diseases, Osaka University, Osaka 565-0871, Japan
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21
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Duszenko M, Kang X, Böhme U, Hömke R, Lehner M. In vitro translation in a cell-free system from Trypanosoma brucei yields glycosylated and glycosylphosphatidylinositol-anchored proteins. EUROPEAN JOURNAL OF BIOCHEMISTRY 1999; 266:789-97. [PMID: 10583372 DOI: 10.1046/j.1432-1327.1999.00897.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
African trypanosomes escape many cellular and unspecific immune reactions by the expression of a protective barrier formed from a repertoire of several hundred genes encoding immunologically distinct variant surface glycoproteins (VSGs). All mature VSGs are glycosylphosphatidylionositol-anchored and N-glycosylated. To study trypanosome-specific post-translational modifications of VSG, a cell-free system capable of in vitro translation, translocation into the rough endoplasmic reticulum, N-glycosylation and glycosylphosphatidylinositol-anchor addition was established using lysates of the bloodstream form of Trypanosoma brucei. Monitoring protein synthesis by [35S]methionine incorporation, labeled protein bands were readily detected by fluorography following SDS/PAGE. Appearance of these bands increased during a time-course of 45 min and was sensitive to cycloheximide but not chloramphenicol treatment. Efficiency of this system, in terms of incorporation of radiolabeled amino acids into newly formed proteins, is similar to reticulocyte lysates. The system does not, however, allow initiation of protein synthesis. Depending on the clone used, immunoprecipitation revealed one or two newly formed VSG bands. Upon digestion with N-glycosidase F these bands resulted in a single band of a lower apparent molecular mass, indicating that newly synthesized VSG underwent translocation and glycosylation in the cell-free system. Biotinylation of VSG and a combination of precipitation with immobilized avidin and detection of VSG using antibodies specific for clones and cross-reacting determinants revealed that newly formed VSG contained the glycosylphosphatidylinositol anchor.
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Affiliation(s)
- M Duszenko
- Physiologisch-chemisches Institut der Universität Tübingen, Germany.
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22
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Sharma DK, Vidugiriene J, Bangs JD, Menon AK. A cell-free assay for glycosylphosphatidylinositol anchoring in African trypanosomes. Demonstration of a transamidation reaction mechanism. J Biol Chem 1999; 274:16479-86. [PMID: 10347210 DOI: 10.1074/jbc.274.23.16479] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We established an in vitro assay for the addition of glycosyl-phosphatidylinositol (GPI) anchors to proteins using procyclic trypanosomes engineered to express GPI-anchored variant surface glycoprotein (VSG). The assay is based on the premise that small nucleophiles, such as hydrazine, can substitute for the GPI moiety and effect displacement of the membrane anchor of a GPI-anchored protein or pro-protein causing release of the protein into the aqueous medium. Cell membranes containing pulse-radiolabeled VSG were incubated with hydrazine, and the VSG released from the membranes was measured by carbonate extraction, immunoprecipitation, and SDS-polyacrylamide gel electrophoresis/fluorography. Release of VSG was time- and temperature-dependent, was stimulated by hydrazine, and occurred only for VSG molecules situated in early compartments of the secretory pathway. No nucleophile-induced VSG release was seen in membranes prepared from cells expressing a VSG variant with a conventional transmembrane anchor (i.e. a nonfunctional GPI signal sequence). Pro-VSG was shown to be a substrate in the reaction by assaying membranes prepared from cells treated with mannosamine, a GPI biosynthesis inhibitor. When a biotinylated derivative of hydrazine was used instead of hydrazine, the released VSG could be precipitated with streptavidin-agarose, indicating that the biotin moiety was covalently incorporated into the protein. Hydrazine was shown to block the C terminus of the released VSG hydrazide because the released material, unlike a truncated form of VSG lacking a GPI signal sequence, was not susceptible to proteolysis by carboxypeptidases. These results firmly establish that the released material in our assay is VSG hydrazide and strengthen the proof that GPI anchoring proceeds via a transamidation reaction mechanism. The reaction could be inhibited with sulfhydryl alkylating reagents, suggesting that the transamidase enzyme contains a functionally important sulfhydryl residue.
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Affiliation(s)
- D K Sharma
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin, USA.
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23
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Vidugiriene J, Sharma DK, Smith TK, Baumann NA, Menon AK. Segregation of glycosylphosphatidylinositol biosynthetic reactions in a subcompartment of the endoplasmic reticulum. J Biol Chem 1999; 274:15203-12. [PMID: 10329729 DOI: 10.1074/jbc.274.21.15203] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glycosylphosphatidylinositols (GPIs) are synthesized in the endoplasmic reticulum (ER) via the sequential addition of monosaccharides, fatty acid, and phosphoethanolamine(s) to phosphatidylinositol (PI). While attempting to establish a mammalian cell-free system for GPI biosynthesis, we found that the assembly of mannosylated GPI species was impaired when purified ER preparations were substituted for unfractionated cell lysates as the enzyme source. To explore this problem we analyzed the distribution of the various GPI biosynthetic reactions in subcellular fractions prepared from homogenates of mammalian cells. The results indicate the following: (i) the initial reaction of GPI assembly, i.e. the transfer of GlcNAc to PI to form GlcNAc-PI, is uniformly distributed in the ER; (ii) the second step of the pathway, i.e. de-N-acetylation of GlcNAc-PI to yield GlcN-PI, is largely confined to a subcompartment of the ER that appears to be associated with mitochondria; (iii) the mitochondria-associated ER subcompartment is enriched in enzymatic activities involved in the conversion of GlcN-PI to H5 (a singly mannosylated GPI structure containing one phosphoethanolamine side chain; and (iv) the mitochondria-associated ER subcompartment, unlike bulk ER, is capable of the de novo synthesis of H5 from UDP-GlcNAc and PI. The confinement of these GPI biosynthetic reactions to a domain of the ER provides another example of the compositional and functional heterogeneity of the ER. The implications of these findings for GPI assembly are discussed.
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Affiliation(s)
- J Vidugiriene
- Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706-1569, USA
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24
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Tiede A, Bastisch I, Schubert J, Orlean P, Schmidt RE. Biosynthesis of glycosylphosphatidylinositols in mammals and unicellular microbes. Biol Chem 1999; 380:503-23. [PMID: 10384957 DOI: 10.1515/bc.1999.066] [Citation(s) in RCA: 97] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Membrane anchoring of cell surface proteins via glycosylphosphatidylinositol (GPI) occurs in all eukaryotic organisms. In addition, GPI-related glycophospholipids are important constituents of the glycan coat of certain protozoa. Defects in GPI biosynthesis can retard, if not abolish growth of these organisms. In humans, a defect in GPI biosynthesis can cause paroxysmal nocturnal hemoglobinuria (PNH), a severe acquired bone marrow disorder. Here, we review advances in the characterization of GPI biosynthesis in parasitic protozoa, yeast and mammalian cells. The GPI core structure as well as the major steps in its biosynthesis are conserved throughout evolution. However, there are significant biosynthetic differences between mammals and microbes. First indications are that these differences could be exploited as targets in the design of novel pharmacotherapeutics that selectively inhibit GPI biosynthesis in unicellular microbes.
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Affiliation(s)
- A Tiede
- Department of Clinical Immunology, Hannover Medical School, Germany
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25
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Spiller OB, Harris CL, Morgan BP. Efficient generation of monoclonal antibodies against surface-expressed proteins by hyperexpression in rodent cells. J Immunol Methods 1999; 224:51-60. [PMID: 10357206 DOI: 10.1016/s0022-1759(99)00008-3] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The generation of antibodies is one of the first requirements in the characterisation of a newly cloned protein. However, this requires expression and purification of the protein in sufficient yield and purity for immunisation of animals and screening of fusion wells. Even with the development of highly efficient protocols based upon incorporation of specific peptide tags, this can be a tedious and time-consuming process. In an effort to improve the speed and efficiency of obtaining antibodies reactive with newly cloned proteins we have developed an approach based upon the expression of the protein at high level in cell lines originating from the species to be used for immunisation. To illustrate this approach we describe the generation of antibodies against two recently cloned proteins that are normally expressed at the membrane, the rat and mouse analogues of human decay accelerating factor (DAF; CD55). However, the strategy is applicable not only to membrane proteins but also to other proteins which can be expressed on the cell membrane by incorporating at the carboxy terminus the signal sequence for glycosyl phosphatidylinositol (GPI) anchor addition derived from DAF or another GPI-anchored protein. The strategy also permits rapid and efficient screening using flow cytometry on expressing cells.
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Affiliation(s)
- O B Spiller
- Department of Medical Biochemistry, University of Wales College of Medicine, Heath Park, Cardiff, UK.
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26
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Aceto J, Kieber-Emmons T, Cines DB. Carboxy-terminal processing of the urokinase receptor: implications for substrate recognition and glycosylphosphatidylinositol anchor addition. Biochemistry 1999; 38:992-1001. [PMID: 9893995 DOI: 10.1021/bi9810914] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Proteins linked to cell membranes by a glycosylphosphatidylinositol (GPI) anchor must first undergo cleavage by a putative transamidase between the omega and omega + 1 positions within a proposed small amino acid (SAD) domain in the carboxy terminus of the nascent polypeptide. The requirements for such processing, defined in an engineered placental alkaline phosphatase construct (miniPLAP), suggest the SAD domain functions as an autonomous unit within the context of an otherwise permissive carboxy-terminal sequence with only certain amino acids tolerated at the omega, omega + 1, and omega + 2 positions. To test whether this hypothesis could be generalized, we engineered a chimeric molecule containing the extracellular domain of miniPLAP and the carboxy-terminal portion of the urokinase receptor (MP/uPAR) into which various amino acid substitutions were introduced. The variant proteins were translated and metabolically labeled in vitro using a cell-free translation system that contains the enzymatic machinery required for carboxy-terminal processing and GPI anchor addition. The results of this study indicate that the SAD domain functions as an independent, but not an autonomous, unit. The requirements for processing in miniPLAP and MP/uPAR differed markedly in some respects, in part due to the influence of the amino acid at the omega + 4 position which both modified cleavage between the omega and omega + 1 positions and permitted a second cleavage site to be generated in some cases. In addition, substitution of bulky hydrophobic amino acids in series at the omega + 2 and omega + 3 positions inhibited carboxy-terminal processing in a dose-dependent manner, suggesting the presence of a critical docking site adjacent to the cleavage site. These results suggest the carboxy-terminal transamidase recognizes a more extended structure similar to the mechanism proposed for serine proteases. Further, the data provide a potential means for isolating the transamidase.
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Affiliation(s)
- J Aceto
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia 19104, USA
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27
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Chen R, Walter EI, Parker G, Lapurga JP, Millan JL, Ikehara Y, Udenfriend S, Medof ME. Mammalian glycophosphatidylinositol anchor transfer to proteins and posttransfer deacylation. Proc Natl Acad Sci U S A 1998; 95:9512-7. [PMID: 9689111 PMCID: PMC21369 DOI: 10.1073/pnas.95.16.9512] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
The glycophosphatidylinositol (GPI) anchors of proteins expressed on human erythrocytes and nucleated cells differ with respect to acylation of an inositol hydroxyl group, a structural feature that modulates their cleavability by PI-specific phospholipase C (PI-PLC). To determine how this GPI anchor modification is regulated, the precursor and protein-associated GPIs in two K562 cell transfectants (ATCC and .48) exhibiting alternatively PI-PLC-sensitive and resistant surface proteins were analyzed and the temporal relationship between GPI protein transfer and acquisition of PI-PLC sensitivity was determined. Nondenaturing PAGE analyses demonstrated that, whereas in .48 transfectants the GPI anchors in decay accelerating factor (DAF) and placental alkaline phosphatase (PLAP) were >95% acylated, in ATCC transfectants, they were 60 and 33% unsubstituted, respectively. In contrast, TLC analyses revealed that putative GPI donors in the two lines were identical and were >/=95% acylated. Studies of de novo DAF biosynthesis in HeLa cells bearing proteins with >90% unacylated anchors showed that within 5 min at 37 degreesC (or at 18 degreesC, which does not permit endoplasmic reticilum exit), >50% of the anchor in nascent 44-kDa proDAF protein exhibited PI-PLC sensitivity. In vitro analyses of the microsomal processing of miniPLAP, a truncated PLAP reporter protein, demonstrated that the anchor donor initially transferred to prominiPLAP was acylated and then progressively was deacylated. These findings indicate that (i) the anchor moiety that initially transfers to nascent proteins is acylated, (ii) inositol acylation in mature surface proteins is regulated via posttransfer deacylation, which in general is cell-specific but also can be protein-dependent, and (iii) deacylation occurs in the endoplasmic reticulum immediately after GPI transfer.
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Affiliation(s)
- R Chen
- Institute of Pathology, Case Western Reserve University, 2085 Adelbert Road, Cleveland, OH, 44106, USA
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28
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Ellis JA, Luzio JP. Identification and characterization of a novel protein (p137) which transcytoses bidirectionally in Caco-2 cells. J Biol Chem 1995; 270:20717-23. [PMID: 7657653 DOI: 10.1074/jbc.270.35.20717] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Antisera raised against detergent-extracted membrane fractions from the human intestinal epithelial cell line Caco-2 were used to screen a human colon cDNA library in a bacteriophage expression vector. This led to the identification, molecular cloning, and sequencing of a novel plasma membrane protein (p137) which was present in approximately equal amounts on the basolateral and apical surfaces of the cell. The pattern of extraction of p137 from membranes by Triton X-114 and its release from membranes after incubation with phosphatidylinositol-specific phospholipase C were consistent with it being a glycosylphosphatidylinositol-anchored membrane protein. Using antibodies raised against bacterial fusion proteins, it was shown that p137 was present on the cell surface as a reducible homodimer of 137 kDa subunits. There was constitutive release of p137 into the culture medium as a non-reducible 280-kDa entity. Pulse-chase experiments showed that newly synthesized p137 appeared at the basolateral side of a Caco-2 cell layer before appearing at the apical domain. Domain-specific surface biotinylation of Caco-2 cells at 4 degrees C, followed by chasing at 37 degrees C, demonstrated that p137 is capable of transcytosing in both directions across Caco-2 cells. The unusual plasma membrane domain distribution of this glycosylphosphatidylinositol-linked protein and its transcytosis characteristics demonstrate the existence of a previously uncharacterized apical to basolateral transcytotic pathway in Caco-2 cells.
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Affiliation(s)
- J A Ellis
- Department of Clinical Biochemistry, University of Cambridge, Addenbrooke's Hospital, United Kingdom
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29
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Maxwell SE, Ramalingam S, Gerber LD, Brink L, Udenfriend S. An active carbonyl formed during glycosylphosphatidylinositol addition to a protein is evidence of catalysis by a transamidase. J Biol Chem 1995; 270:19576-82. [PMID: 7642644 DOI: 10.1074/jbc.270.33.19576] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Glycosylphosphatidylinositol (GPI) substitution is now recognized to be a ubiquitous method of anchoring a protein to membranes in eukaryotes. The structure of GPI and its biosynthetic pathways are known and the signals in a nascent protein for GPI addition have been elucidated. The enzyme(s) responsible for GPI addition with release of a COOH-terminal signal peptide has been considered to be a transamidase but has yet to be isolated, and evidence that it is a transamidase is indirect. The experiments reported here show that hydrazine and hydroxylamine, in the presence of rough microsomal membranes, catalyze the conversion of the pro form of the engineered protein miniplacental alkaline phosphatase (prominiPLAP) to mature forms from which the COOH-terminal signal peptide has been cleaved, apparently at the same site but without the addition of GPI. The products, presumable the hydrazide or hydroxamate of miniPLAP, have yet to be characterized definitively. However, our demonstration of enzyme-catalyzed cleavage of the signal peptide in the presence of the small nucleophiles, even in the absence of an energy source, is evidence of an activated carbonyl intermediate which is the hallmark of a transamidase.
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Affiliation(s)
- S E Maxwell
- Roche Institute of Molecular Biology, Roche Research Center, Nutley, New Jersey 07110-1199, USA
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30
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Udenfriend S, Kodukula K. Prediction of omega site in nascent precursor of glycosylphosphatidylinositol protein. Methods Enzymol 1995; 250:571-82. [PMID: 7651179 DOI: 10.1016/0076-6879(95)50098-7] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- S Udenfriend
- Roche Research Center, Roche Institute of Molecular Biology, Nutley, New Jersey 07110, USA
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31
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Kinoshita T, Inoue N, Takeda J. Defective glycosyl phosphatidylinositol anchor synthesis and paroxysmal nocturnal hemoglobinuria. Adv Immunol 1995; 60:57-103. [PMID: 8607375 DOI: 10.1016/s0065-2776(08)60584-2] [Citation(s) in RCA: 122] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- T Kinoshita
- Department of Immunoregulation, Osaka University, Japan
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32
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Kodukula K, Maxwell SE, Udenfriend S. Processing of nascent proteins to glycosylphosphatidylinositol-anchored forms in cell-free systems. Methods Enzymol 1995; 250:536-47. [PMID: 7651176 DOI: 10.1016/0076-6879(95)50095-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- K Kodukula
- Department of Natural Products Research, Bristol-Myers Squibb Pharmaceutical Research Institute, Wallingford, Connecticut 06492, USA
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Gerber L, Kodukula K, Udenfriend S. Phosphatidylinositol glycan (PI-G) anchored membrane proteins. Amino acid requirements adjacent to the site of cleavage and PI-G attachment in the COOH-terminal signal peptide. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(19)49819-0] [Citation(s) in RCA: 139] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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Takami N, Oda K, Ikehara Y. Aberrant processing of alkaline phosphatase precursor caused by blocking the synthesis of glycosylphosphatidylinositol. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)48392-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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