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Li D. Structure and Function of the Glycosylphosphatidylinositol Transamidase, a Transmembrane Complex Catalyzing GPI Anchoring of Proteins. Subcell Biochem 2024; 104:425-458. [PMID: 38963495 DOI: 10.1007/978-3-031-58843-3_16] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/05/2024]
Abstract
Glycosylphosphatidylinositol (GPI) anchoring of proteins is a ubiquitous posttranslational modification in eukaryotic cells. GPI-anchored proteins (GPI-APs) play critical roles in enzymatic, signaling, regulatory, and adhesion processes. Over 20 enzymes are involved in GPI synthesis, attachment to client proteins, and remodeling after attachment. The GPI transamidase (GPI-T), a large complex located in the endoplasmic reticulum membrane, catalyzes the attachment step by replacing a C-terminal signal peptide of proproteins with GPI. In the last three decades, extensive research has been conducted on the mechanism of the transamidation reaction, the components of the GPI-T complex, the role of each subunit, and the substrate specificity. Two recent studies have reported the three-dimensional architecture of GPI-T, which represent the first structures of the pathway. The structures provide detailed mechanisms for assembly that rationalizes previous biochemical results and subunit-dependent stability data. While the structural data confirm the catalytic role of PIGK, which likely uses a caspase-like mechanism to cleave the proproteins, they suggest that unlike previously proposed, GPAA1 is not a catalytic subunit. The structures also reveal a shared cavity for GPI binding. Somewhat unexpectedly, PIGT, a single-pass membrane protein, plays a crucial role in GPI recognition. Consistent with the assembly mechanisms and the active site architecture, most of the disease mutations occur near the active site or the subunit interfaces. Finally, the catalytic dyad is located ~22 Å away from the membrane interface of the GPI-binding site, and this architecture may confer substrate specificity through topological matching between the substrates and the elongated active site. The research conducted thus far sheds light on the intricate processes involved in GPI anchoring and paves the way for further mechanistic studies of GPI-T.
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Affiliation(s)
- Dianfan Li
- CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences (CAS), Shanghai, China.
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2
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Xu Y, Li T, Zhou Z, Hong J, Chao Y, Zhu Z, Zhang Y, Qu Q, Li D. Structures of liganded glycosylphosphatidylinositol transamidase illuminate GPI-AP biogenesis. Nat Commun 2023; 14:5520. [PMID: 37684232 PMCID: PMC10491789 DOI: 10.1038/s41467-023-41281-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2023] [Accepted: 08/25/2023] [Indexed: 09/10/2023] Open
Abstract
Many eukaryotic receptors and enzymes rely on glycosylphosphatidylinositol (GPI) anchors for membrane localization and function. The transmembrane complex GPI-T recognizes diverse proproteins at a signal peptide region that lacks consensus sequence and replaces it with GPI via a transamidation reaction. How GPI-T maintains broad specificity while preventing unintentional cleavage is unclear. Here, substrates- and products-bound human GPI-T structures identify subsite features that enable broad proprotein specificity, inform catalytic mechanism, and reveal a multilevel safeguard mechanism against its promiscuity. In the absence of proproteins, the catalytic site is invaded by a locally stabilized loop. Activation requires energetically unfavorable rearrangements that transform the autoinhibitory loop into crucial catalytic cleft elements. Enzyme-proprotein binding in the transmembrane and luminal domains respectively powers the conformational rearrangement and induces a competent cleft. GPI-T thus integrates various weak specificity regions to form strong selectivity and prevent accidental activation. These findings provide important mechanistic insights into GPI-anchored protein biogenesis.
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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, Chinese Academy of Sciences (CAS), University of CAS, Shanghai, China
| | - Tingting Li
- State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences (CAS), University of CAS, 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, Shanghai, China
| | - Jingjing Hong
- State Key Laboratory of Molecular Biology, CAS Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences (CAS), University of CAS, 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, Shanghai, China
| | - Zhini Zhu
- 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, Shanghai, China
| | - Ying Zhang
- 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, Shanghai, 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, 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, Chinese Academy of Sciences (CAS), University of CAS, Shanghai, China.
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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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Omura F, Takagi M, Kodama Y. Compromised chitin synthesis in lager yeast affects its Congo red resistance and release of mannoproteins from the cells. FEMS Microbiol Lett 2020; 367:5974272. [PMID: 33175116 DOI: 10.1093/femsle/fnaa181] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Accepted: 11/08/2020] [Indexed: 11/14/2022] Open
Abstract
A mutant lager strain resistant to the cell wall-perturbing agent Congo red (CR) was isolated and the genetic alterations underlying CR resistance were investigated by whole genome sequencing. The parental lager strain was found to contain three distinct Saccharomyces cerevisiae (Sc)-type CHS6 (CHitin Synthase-related 6) alleles, two of which have one or two nonsense mutations in the open reading frame, leaving only one functional allele, whereas the functional allele was missing in the isolated CR-resistant strain. On the other hand, the Saccharomyces eubayanus-type CHS6 alleles shared by both the parental and mutant strains appeared to contribute poorly to chitin synthase-activating function. Therefore, the CR resistance of the mutant strain was attributable to the overall compromised activity of CHS6 gene products. The CR-resistant mutant cells exhibited less chitin production on the cell surface and smaller amounts of mannoprotein release into the medium. All these traits, in addition to the CR resistance, were complemented by the functional ScCHS6 gene. It is of great interest whether the frequent nonsense mutations found in ScCHS6 open reading frame in lager yeast strains are a consequence of the domestication process of lager yeast.
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Affiliation(s)
- Fumihiko Omura
- Suntory Global Innovation Center Ltd., 8-1-1 Seikadai, Seika-cho, Soraku-gun, Kyoto 619-0284, Japan
| | - Motoshige Takagi
- Suntory System Technology Ltd., 2-1-5 Doujima, Kita-ku, Osaka-shi, Osaka 530-8204, Japan
| | - Yukiko Kodama
- Suntory Global Innovation Center Ltd., 8-1-1 Seikadai, Seika-cho, Soraku-gun, Kyoto 619-0284, Japan
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Desnoyer N, Howard G, Jong E, Palanivelu R. AtPIG-S, a predicted Glycosylphosphatidylinositol Transamidase subunit, is critical for pollen tube growth in Arabidopsis. BMC PLANT BIOLOGY 2020; 20:380. [PMID: 32811442 PMCID: PMC7437025 DOI: 10.1186/s12870-020-02587-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2020] [Accepted: 08/03/2020] [Indexed: 05/23/2023]
Abstract
BACKGROUND Glycosylphosphatidylinositol (GPI) addition is one of the several post-translational modifications to proteins that increase their affinity for membranes. In eukaryotes, the GPI transamidase complex (GPI-T) catalyzes the attachment of pre-assembled GPI anchors to GPI-anchored proteins (GAPs) through a transamidation reaction. A mutation in AtGPI8 (gpi8-2), the putative catalytic subunit of GPI-T in Arabidopsis, is transmitted normally through the female gametophyte (FG), indicating the FG tolerates loss of GPI transamidation. In contrast, gpi8-2 almost completely abolishes male gametophyte (MG) function. Still, the unexpected finding that gpi8-2 FGs function normally requires further investigation. Additionally, specific developmental defects in the MG caused by loss of GPI transamidation remain poorly characterized. RESULTS Here we investigated the effect of loss of AtPIG-S, another GPI-T subunit, in both gametophytes. Like gpi8-2, we showed that a mutation in AtPIG-S (pigs-1) disrupted synergid localization of LORELEI (LRE), a putative GAP critical for pollen tube reception by the FG. Still, pigs-1 is transmitted normally through the FG. Conversely, pigs-1 severely impaired male gametophyte (MG) function during pollen tube emergence and growth in the pistil. A pPIGS:GFP-PIGS transgene complemented these MG defects and enabled generation of pigs-1/pigs-1 seedlings. However, the pPIGS:GFP-PIGS transgene seemingly failed to rescue the function of AtPIG-S in the sporophyte, as pigs-1/pigs-1, pPIGS:GFP-PIGS seedlings died soon after germination. CONCLUSIONS Characterization of pigs-1 provided further evidence that the FG tolerates loss of GPI transamidation more than the MG and that the MG compared to the FG may be a better haploid system to study the role of GPI-anchoring. Pigs-1 pollen develops normally and thus represent a tool in which GPI anchor biosynthesis and transamidation of GAPs have been uncoupled, offering a potential way to study free GPI in plant development. While previously reported male fertility defects of GPI biosynthesis mutants could have been due either to loss of GPI or GAPs lacking the GPI anchor, our results clarified that the loss of mature GAPs underlie male fertility defects of GPI-deficient pollen grains, as pigs-1 is defective only in the downstream transamidation step.
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Affiliation(s)
- Nicholas Desnoyer
- School of Plant Sciences, University of Arizona, Tucson, AZ, 85721, USA
- Present Address: Department of Plant and Microbial Biology, University of Zurich, Zollikerstrasse 107, CH-8008, Zurich, Switzerland
| | - Gregory Howard
- School of Plant Sciences, University of Arizona, Tucson, AZ, 85721, USA
| | - Emma Jong
- School of Plant Sciences, University of Arizona, Tucson, AZ, 85721, USA
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6
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The soluble domains of Gpi8 and Gaa1, two subunits of glycosylphosphatidylinositol transamidase (GPI-T), assemble into a complex. Arch Biochem Biophys 2017; 633:58-67. [DOI: 10.1016/j.abb.2017.09.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Revised: 09/06/2017] [Accepted: 09/07/2017] [Indexed: 11/23/2022]
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7
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Disulfide Bond Formation and N-Glycosylation Modulate Protein-Protein Interactions in GPI-Transamidase (GPIT). Sci Rep 2017; 8:45912. [PMID: 28374821 PMCID: PMC5379210 DOI: 10.1038/srep45912] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Accepted: 03/06/2017] [Indexed: 12/28/2022] Open
Abstract
Glycosylphosphatidylinositol (GPI) transamidase (GPIT), the enzyme that attaches GPI anchors to proteins as they enter the lumen of the endoplasmic reticulum, is a membrane-bound hetero-pentameric complex consisting of Gpi8, Gpi16, Gaa1, Gpi17 and Gab1. Here, we expressed and purified the luminal domain of Saccharomyces cerevisiae (S. cerevisiae) Gpi8 using different expression systems, and examined its interaction with insect cell expressed luminal domain of S. cerevisiae Gpi16. We found that the N-terminal caspase-like domain of Gpi8 forms a disulfide-linked dimer, which is strengthened by N-glycosylation. The non-core domain of Gpi8 following the caspase-like domain inhibits this dimerization. In contrast to the previously reported disulfide linkage between Gpi8 and Gpi16 in human and trypanosome GPIT, our data show that the luminal domains of S. cerevisiae Gpi8 and S. cerevisiae Gpi16 do not interact directly, nor do they form a disulfide bond in the intact S. cerevisiae GPIT. Our data suggest that subunit interactions within the GPIT complex from different species may vary, a feature that should be taken into account in future structural and functional studies.
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8
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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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9
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Orlean P. Architecture and biosynthesis of the Saccharomyces cerevisiae cell wall. Genetics 2012; 192:775-818. [PMID: 23135325 PMCID: PMC3522159 DOI: 10.1534/genetics.112.144485] [Citation(s) in RCA: 296] [Impact Index Per Article: 24.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2012] [Accepted: 08/06/2012] [Indexed: 01/02/2023] Open
Abstract
The wall gives a Saccharomyces cerevisiae cell its osmotic integrity; defines cell shape during budding growth, mating, sporulation, and pseudohypha formation; and presents adhesive glycoproteins to other yeast cells. The wall consists of β1,3- and β1,6-glucans, a small amount of chitin, and many different proteins that may bear N- and O-linked glycans and a glycolipid anchor. These components become cross-linked in various ways to form higher-order complexes. Wall composition and degree of cross-linking vary during growth and development and change in response to cell wall stress. This article reviews wall biogenesis in vegetative cells, covering the structure of wall components and how they are cross-linked; the biosynthesis of N- and O-linked glycans, glycosylphosphatidylinositol membrane anchors, β1,3- and β1,6-linked glucans, and chitin; the reactions that cross-link wall components; and the possible functions of enzymatic and nonenzymatic cell wall proteins.
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Affiliation(s)
- Peter Orlean
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
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10
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Defining the boundaries of species specificity for the Saccharomyces cerevisiae glycosylphosphatidylinositol transamidase using a quantitative in vivo assay. Biosci Rep 2012; 32:577-86. [PMID: 22938202 PMCID: PMC3497722 DOI: 10.1042/bsr20120064] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
In eukaryotes, GPI (glycosylphosphatidylinositol) lipid anchoring of proteins is an abundant post-translational modification. The attachment of the GPI anchor is mediated by GPI-T (GPI transamidase), a multimeric, membrane-bound enzyme located in the ER (endoplasmic reticulum). Upon modification, GPI-anchored proteins enter the secretory pathway and ultimately become tethered to the cell surface by association with the plasma membrane and, in yeast, by covalent attachment to the outer glucan layer. This work demonstrates a novel in vivo assay for GPI-T. Saccharomyces cerevisiae INV (invertase), a soluble secreted protein, was converted into a substrate for GPI-T by appending the C-terminal 21 amino acid GPI-T signal sequence from the S. cerevisiae Yapsin 2 [Mkc7p (Y21)] on to the C-terminus of INV. Using a colorimetric assay and biochemical partitioning, extracellular presentation of GPI-anchored INV was shown. Two human GPI-T signal sequences were also tested and each showed diminished extracellular INV activity, consistent with lower levels of GPI anchoring and species specificity. Human/fungal chimaeric signal sequences identified a small region of five amino acids that was predominantly responsible for this species specificity.
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11
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12
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Ghazal G, Gagnon J, Jacques PE, Landry JR, Robert F, Elela SA. Yeast RNase III triggers polyadenylation-independent transcription termination. Mol Cell 2009; 36:99-109. [PMID: 19818713 DOI: 10.1016/j.molcel.2009.07.029] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2008] [Revised: 06/22/2009] [Accepted: 07/22/2009] [Indexed: 12/17/2022]
Abstract
Transcription termination of messenger RNA (mRNA) is normally achieved by polyadenylation followed by Rat1p-dependent 5'-3' exoribonuleolytic degradation of the downstream transcript. Here we show that the yeast ortholog of the dsRNA-specific ribonuclease III (Rnt1p) may trigger Rat1p-dependent termination of RNA transcripts that fail to terminate near polyadenylation signals. Rnt1p cleavage sites were found downstream of several genes, and the deletion of RNT1 resulted in transcription readthrough. Inactivation of Rat1p impaired Rnt1p-dependent termination and resulted in the accumulation of 3' end cleavage products. These results support a model for transcription termination in which cotranscriptional cleavage by Rnt1p provides access for exoribonucleases in the absence of polyadenylation signals.
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Affiliation(s)
- Ghada Ghazal
- RNA Group, Département de Microbiologie et d'Infectiologie, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, QC J1H 5N4, Canada
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Meitzler JL, Gray JJ, Hendrickson TL. Truncation of the caspase-related subunit (Gpi8p) of Saccharomyces cerevisiae GPI transamidase: Dimerization revealed. Arch Biochem Biophys 2007; 462:83-93. [PMID: 17475206 DOI: 10.1016/j.abb.2007.03.035] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2007] [Revised: 03/15/2007] [Accepted: 03/16/2007] [Indexed: 11/24/2022]
Abstract
Eukaryotic proteins can be post-translationally modified with a glycosylphosphatidylinositol (GPI) membrane anchor. This modification reaction is catalyzed by GPI transamidase (GPI-T), a multimeric, membrane-bound enzyme. Gpi8p, an essential component of GPI-T, shares low sequence similarity with caspases and contains all or part of the enzyme's active site [U. Meyer, M. Benghezal, I. Imhof, A. Conzelmann, Biochemistry 39 (2000) 3461-3471]. Structural predictions suggest that the soluble portion of Gpi8p is divided into two domains: a caspase-like domain that contains the active site machinery and a second, smaller domain of unknown function. Based on these predictions, we evaluated a soluble truncation of Gpi8p (Gpi8(23-306)). Dimerization was investigated due to the known proclivity of caspases to homodimerize; a Gpi8(23-306) homodimer was detected by native gel and confirmed by mass spectrometry and N-terminal sequencing. Mutations at the putative caspase-like dimerization interface disrupted dimer formation. When combined, these results demonstrate an organizational similarity between Gpi8p and caspases.
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Affiliation(s)
- Jennifer L Meitzler
- Department of Chemistry, Remsen Hall, Johns Hopkins University, Baltimore, MD 21218, USA
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Orlean P, Menon AK. Thematic review series: lipid posttranslational modifications. GPI anchoring of protein in yeast and mammalian cells, or: how we learned to stop worrying and love glycophospholipids. J Lipid Res 2007; 48:993-1011. [PMID: 17361015 DOI: 10.1194/jlr.r700002-jlr200] [Citation(s) in RCA: 273] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Glycosylphosphatidylinositol (GPI) anchoring of cell surface proteins is the most complex and metabolically expensive of the lipid posttranslational modifications described to date. The GPI anchor is synthesized via a membrane-bound multistep pathway in the endoplasmic reticulum (ER) requiring >20 gene products. The pathway is initiated on the cytoplasmic side of the ER and completed in the ER lumen, necessitating flipping of a glycolipid intermediate across the membrane. The completed GPI anchor is attached to proteins that have been translocated across the ER membrane and that display a GPI signal anchor sequence at the C terminus. GPI proteins transit the secretory pathway to the cell surface; in yeast, many become covalently attached to the cell wall. Genes encoding proteins involved in all but one of the predicted steps in the assembly of the GPI precursor glycolipid and its transfer to protein in mammals and yeast have now been identified. Most of these genes encode polytopic membrane proteins, some of which are organized in complexes. The steps in GPI assembly, and the enzymes that carry them out, are highly conserved. GPI biosynthesis is essential for viability in yeast and for embryonic development in mammals. In this review, we describe the biosynthesis of mammalian and yeast GPIs, their transfer to protein, and their subsequent processing.
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Affiliation(s)
- Peter Orlean
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
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15
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Pittet M, Conzelmann A. Biosynthesis and function of GPI proteins in the yeast Saccharomyces cerevisiae. Biochim Biophys Acta Mol Cell Biol Lipids 2007; 1771:405-20. [PMID: 16859984 DOI: 10.1016/j.bbalip.2006.05.015] [Citation(s) in RCA: 163] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2006] [Revised: 05/20/2006] [Accepted: 05/22/2006] [Indexed: 11/28/2022]
Abstract
Like most other eukaryotes, Saccharomyces cerevisiae harbors a GPI anchoring machinery and uses it to attach proteins to membranes. While a few GPI proteins reside permanently at the plasma membrane, a majority of them gets further processed and is integrated into the cell wall by a covalent attachment to cell wall glucans. The GPI biosynthetic pathway is necessary for growth and survival of yeast cells. The GPI lipids are synthesized in the ER and added onto proteins by a pathway comprising 12 steps, carried out by 23 gene products, 19 of which are essential. Some of the estimated 60 GPI proteins predicted from the genome sequence serve enzymatic functions required for the biosynthesis and the continuous shape adaptations of the cell wall, others seem to be structural elements of the cell wall and yet others mediate cell adhesion. Because of its genetic tractability S. cerevisiae is an attractive model organism not only for studying GPI biosynthesis in general, but equally for investigating the intracellular transport of GPI proteins and the peculiar role of GPI anchoring in the elaboration of fungal cell walls.
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Affiliation(s)
- Martine Pittet
- Department of Medicine, Division of Biochemistry, Chemin du Musée 5, CH-1700 Fribourg, Switzerland
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16
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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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Krause F. Detection and analysis of protein–protein interactions in organellar and prokaryotic proteomes by native gel electrophoresis: (Membrane) protein complexes and supercomplexes. Electrophoresis 2006; 27:2759-81. [PMID: 16817166 DOI: 10.1002/elps.200600049] [Citation(s) in RCA: 144] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
It is an essential and challenging task to unravel protein-protein interactions in their actual in vivo context. Native gel systems provide a separation platform allowing the analysis of protein complexes on a rather proteome-wide scale in a single experiment. This review focus on blue-native (BN)-PAGE as the most versatile and successful gel-based approach to separate soluble and membrane protein complexes of intricate protein mixtures derived from all biological sources. BN-PAGE is a charge-shift method with a running pH of 7.5 relying on the gentle binding of anionic CBB dye to all membrane and many soluble protein complexes, leading to separation of protein species essentially according to their size and superior resolution than other fractionation techniques can offer. The closely related colorless-native (CN)-PAGE, whose applicability is restricted to protein species with intrinsic negative net charge, proved to provide an especially mild separation capable of preserving weak protein-protein interactions better than BN-PAGE. The essential conditions determining the success of detecting protein-protein interactions are the sample preparations, e.g. the efficiency/mildness of the detergent solubilization of membrane protein complexes. A broad overview about the achievements of BN- and CN-PAGE studies to elucidate protein-protein interactions in organelles and prokaryotes is presented, e.g. the mitochondrial protein import machinery and oxidative phosphorylation supercomplexes. In many cases, solubilization with digitonin was demonstrated to facilitate an efficient and particularly gentle extraction of membrane protein complexes prone to dissociation by treatment with other detergents. In general, analyses of protein interactomes should be carried out by both BN- and CN-PAGE.
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Affiliation(s)
- Frank Krause
- Department of Chemistry, Physical Biochemistry, Darmstadt University of Technology, Germany.
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