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Komath SS. To each its own: Mechanisms of cross-talk between GPI biosynthesis and cAMP-PKA signaling in Candida albicans versus Saccharomyces cerevisiae. J Biol Chem 2024; 300:107444. [PMID: 38838772 DOI: 10.1016/j.jbc.2024.107444] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2024] [Revised: 05/24/2024] [Accepted: 05/29/2024] [Indexed: 06/07/2024] Open
Abstract
Candida albicans is an opportunistic fungal pathogen that can switch between yeast and hyphal morphologies depending on the environmental cues it receives. The switch to hyphal form is crucial for the establishment of invasive infections. The hyphal form is also characterized by the cell surface expression of hyphae-specific proteins, many of which are GPI-anchored and important determinants of its virulence. The coordination between hyphal morphogenesis and the expression of GPI-anchored proteins is made possible by an interesting cross-talk between GPI biosynthesis and the cAMP-PKA signaling cascade in the fungus; a parallel interaction is not found in its human host. On the other hand, in the nonpathogenic yeast, Saccharomyces cerevisiae, GPI biosynthesis is shut down when filamentation is activated and vice versa. This too is achieved by a cross-talk between GPI biosynthesis and cAMP-PKA signaling. How are diametrically opposite effects obtained from the cross-talk between two reasonably well-conserved pathways present ubiquitously across eukarya? This Review attempts to provide a model to explain these differences. In order to do so, it first provides an overview of the two pathways for the interested reader, highlighting the similarities and differences that are observed in C. albicans versus the well-studied S. cerevisiae model, before going on to explain how the different mechanisms of regulation are effected. While commonalities enable the development of generalized theories, it is hoped that a more nuanced approach, that takes into consideration species-specific differences, will enable organism-specific understanding of these processes and contribute to the development of targeted therapies.
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Glycosylphosphatidylinositol Anchor Biosynthesis Pathway-Related Protein GPI7 Is Required for the Vegetative Growth and Pathogenicity of Colletotrichum graminicola. Int J Mol Sci 2022; 23:ijms23062985. [PMID: 35328406 PMCID: PMC8949851 DOI: 10.3390/ijms23062985] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Revised: 03/07/2022] [Accepted: 03/08/2022] [Indexed: 01/04/2023] Open
Abstract
Glycosylphosphatidylinositol (GPI) anchoring is a common post-translational modification in eukaryotic cells and has been demonstrated to have a wide range of biological functions, such as signal transduction, cellular adhesion, protein transport, immune response, and maintaining cell wall integrity. More than 25 proteins have been proven to participate in the GPI anchor synthesis pathway which occurs in the cytoplasmic and the luminal face of the ER membrane. However, the essential proteins of the GPI anchor synthesis pathway are still less characterized in maize pathogen Colletotrichum graminicola. In the present study, we analyzed the biological function of the GPI anchor synthesis pathway-related gene, CgGPI7, that encodes an ethanolamine phosphate transferase, which is localized in ER. The vegetative growth and conidia development of the ΔCgGPI7 mutant was significantly impaired in C. graminicola. and qRT-PCR results showed that the transcriptional level of CgGPI7 was specifically induced in the initial infection stage and that the pathogenicity of ΔCgGPI7 mutant was also significantly decreased compared with the wild type. Furthermore, the ΔCgGPI7 mutant displayed more sensitivity to cell wall stresses, suggesting that CgGPI7 may play a role in the cell wall integrity of C. graminicola. Cell wall synthesis-associated genes were also quantified in the ΔCgGPI7 mutant, and the results showed that chitin and β-1,3-glucans synthesis genes were significantly up-regulated in ΔCgGPI7 mutants. Our results suggested that CgGPI7 is required for vegetative growth and pathogenicity and might depend on the cell wall integrity of C. graminicola.
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Role of Protein Glycosylation in Interactions of Medically Relevant Fungi with the Host. J Fungi (Basel) 2021; 7:jof7100875. [PMID: 34682296 PMCID: PMC8541085 DOI: 10.3390/jof7100875] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2021] [Revised: 10/08/2021] [Accepted: 10/11/2021] [Indexed: 01/09/2023] Open
Abstract
Protein glycosylation is a highly conserved post-translational modification among organisms. It plays fundamental roles in many biological processes, ranging from protein trafficking and cell adhesion to host–pathogen interactions. According to the amino acid side chain atoms to which glycans are linked, protein glycosylation can be divided into two major categories: N-glycosylation and O-glycosylation. However, there are other types of modifications such as the addition of GPI to the C-terminal end of the protein. Besides the importance of glycoproteins in biological functions, they are a major component of the fungal cell wall and plasma membrane and contribute to pathogenicity, virulence, and recognition by the host immunity. Given that this structure is absent in host mammalian cells, it stands as an attractive target for developing selective compounds for the treatment of fungal infections. This review focuses on describing the relationship between protein glycosylation and the host–immune interaction in medically relevant fungal species.
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Jenni A, Knüsel S, Nagar R, Benninger M, Häner R, Ferguson MAJ, Roditi I, Menon AK, Bütikofer P. Elimination of GPI2 suppresses glycosylphosphatidylinositol GlcNAc transferase activity and alters GPI glycan modification in Trypanosoma brucei. J Biol Chem 2021; 297:100977. [PMID: 34284059 PMCID: PMC8358704 DOI: 10.1016/j.jbc.2021.100977] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2021] [Revised: 06/20/2021] [Accepted: 07/16/2021] [Indexed: 01/14/2023] Open
Abstract
Many eukaryotic cell-surface proteins are post-translationally modified by a glycosylphosphatidylinositol (GPI) moiety that anchors them to the cell membrane. The biosynthesis of GPI anchors is initiated in the endoplasmic reticulum by transfer of GlcNAc from UDP-GlcNAc to phosphatidylinositol. This reaction is catalyzed by GPI GlcNAc transferase, a multisubunit complex comprising the catalytic subunit Gpi3/PIG-A as well as at least five other subunits, including the hydrophobic protein Gpi2, which is essential for the activity of the complex in yeast and mammals, but the function of which is not known. To investigate the role of Gpi2, we exploited Trypanosoma brucei (Tb), an early diverging eukaryote and important model organism that initially provided the first insights into GPI structure and biosynthesis. We generated insect-stage (procyclic) trypanosomes that lack TbGPI2 and found that in TbGPI2-null parasites, (i) GPI GlcNAc transferase activity is reduced, but not lost, in contrast with yeast and human cells, (ii) the GPI GlcNAc transferase complex persists, but its architecture is affected, with loss of at least the TbGPI1 subunit, and (iii) the GPI anchors of procyclins, the major surface proteins, are underglycosylated when compared with their WT counterparts, indicating the importance of TbGPI2 for reactions that occur in the Golgi apparatus. Immunofluorescence microscopy localized TbGPI2 not only to the endoplasmic reticulum but also to the Golgi apparatus, suggesting that in addition to its expected function as a subunit of the GPI GlcNAc transferase complex, TbGPI2 may have an enigmatic noncanonical role in Golgi-localized GPI anchor modification in trypanosomes.
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Affiliation(s)
- Aurelio Jenni
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland; Graduate School for Chemical and Biomedical Sciences, University of Bern, Bern, Switzerland
| | - Sebastian Knüsel
- Institute of Cell Biology, University of Bern, Bern, Switzerland
| | - Rupa Nagar
- Wellcome Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | | | - Robert Häner
- Department for Chemistry and Biochemistry, University of Bern, Bern, Switzerland
| | - Michael A J Ferguson
- Wellcome Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Isabel Roditi
- Institute of Cell Biology, University of Bern, Bern, Switzerland
| | - Anant K Menon
- Department of Biochemistry, Weill Cornell Medical College, New York, New York, USA
| | - Peter Bütikofer
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland.
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Potential Physiological Relevance of ERAD to the Biosynthesis of GPI-Anchored Proteins in Yeast. Int J Mol Sci 2021; 22:ijms22031061. [PMID: 33494405 PMCID: PMC7865462 DOI: 10.3390/ijms22031061] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 01/18/2021] [Accepted: 01/19/2021] [Indexed: 12/19/2022] Open
Abstract
Misfolded and/or unassembled secretory and membrane proteins in the endoplasmic reticulum (ER) may be retro-translocated into the cytoplasm, where they undergo ER-associated degradation, or ERAD. The mechanisms by which misfolded proteins are recognized and degraded through this pathway have been studied extensively; however, our understanding of the physiological role of ERAD remains limited. This review describes the biosynthesis and quality control of glycosylphosphatidylinositol (GPI)-anchored proteins and briefly summarizes the relevance of ERAD to these processes. While recent studies suggest that ERAD functions as a fail-safe mechanism for the degradation of misfolded GPI-anchored proteins, several pieces of evidence suggest an intimate interaction between ERAD and the biosynthesis of GPI-anchored proteins.
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6
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Vojdani A, Gushgari LR, Vojdani E. Interaction between food antigens and the immune system: Association with autoimmune disorders. Autoimmun Rev 2020; 19:102459. [PMID: 31917265 DOI: 10.1016/j.autrev.2020.102459] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2019] [Accepted: 08/19/2019] [Indexed: 02/08/2023]
Abstract
It has been shown that environmental factors such as infections, chemicals, and diet play a major role in autoimmune diseases; however, relatively little attention has been given to food components as the most prevalent modifiers of these afflictions. This review summarizes the current body of knowledge related to different mechanisms and associations between food proteins/peptides and autoimmune disorders. The primary factor controlling food-related immune reactions is the oral tolerance mechanism. The failure of oral tolerance triggers immune reactivity against dietary antigens, which may initiate or exacerbate autoimmune disease when the food antigen shares homology with human tissue antigens. Because the conformational fit between food antigens and a host's self-determinants has been determined for only a few food proteins, we examined evidence related to the reaction of affinity-purified disease-specific antibody with different food antigens. We also studied the reaction of monoclonal or polyclonal tissue-specific antibodies with various food antigens and the reaction of food-specific antibodies with human tissue antigens. Examining the assembled information, we postulated that chemical modification of food proteins by different toxicants in food may result in immune reaction against modified food proteins that cross-react with tissue antigens, resulting in autoimmune reactivity. Because we are what our microbiome eats, food can change the gut commensals, and toxins can breach the gut barrier, penetrating into different organs where they can initiate autoimmune response. Conversely, there are also foods and supplements that help maintain oral tolerance and microbiome homeostasis. Understanding the potential link between specific food consumption and autoimmunity in humans may lay the foundation for further research about the proper diet in the prevention of autoimmune diseases.
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Affiliation(s)
- Aristo Vojdani
- Immunosciences Lab, Inc., 822 S. Robertson Blvd, Ste. 312, Los Angeles, CA 90035, USA; Department of Preventive Medicine, Loma Linda University, Loma Linda, CA 92350, USA.
| | - Lydia R Gushgari
- Cyrex Laboratories, LLC. 2602 South 24(th) St., Phoenix, AZ 85034, USA.
| | - Elroy Vojdani
- Regenera Medical, 11860 Wilshire Blvd., Ste. 301, Los Angeles, CA 90025, USA.
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7
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Komath SS, Singh SL, Pratyusha VA, Sah SK. Generating anchors only to lose them: The unusual story of glycosylphosphatidylinositol anchor biosynthesis and remodeling in yeast and fungi. IUBMB Life 2019; 70:355-383. [PMID: 29679465 DOI: 10.1002/iub.1734] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Revised: 02/16/2018] [Accepted: 02/22/2018] [Indexed: 02/06/2023]
Abstract
Glycosylphosphatidylinositol (GPI)-anchored proteins (GPI-APs) are present ubiquitously at the cell surface in all eukaryotes. They play a crucial role in the interaction of the cell with its external environment, allowing the cell to receive signals, respond to challenges, and mediate adhesion. In yeast and fungi, they also participate in the structural integrity of the cell wall and are often essential for survival. Roughly four decades after the discovery of the first GPI-APs, this review provides an overview of the insights gained from studies of the GPI biosynthetic pathway and the future challenges in the field. In particular, we focus on the biosynthetic pathway in Saccharomyces cerevisiae, which has for long been studied as a model organism. Where available, we also provide information about the GPI biosynthetic steps in other yeast/ fungi. Although the core structure of the GPI anchor is conserved across organisms, several variations are built into the biosynthetic pathway. The present Review specifically highlights these variations and their implications. There is growing evidence to suggest that several phenotypes are common to GPI deficiency and should be expected in GPI biosynthetic mutants. However, it appears that several phenotypes are unique to a specific step in the pathway and may even be species-specific. These could suggest the points at which the GPI biosynthetic pathway intersects with other important cellular pathways and could be points of regulation. They could be of particular significance in the study of pathogenic fungi and in identification of new and specific antifungal drugs/ drug targets. © 2018 IUBMB Life, 70(5):355-383, 2018.
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Affiliation(s)
| | - Sneh Lata Singh
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, India
| | | | - Sudisht Kumar Sah
- School of Life Sciences, Jawaharlal Nehru University, New Delhi, India
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Jain P, Sethi SC, Pratyusha VA, Garai P, Naqvi N, Singh S, Pawar K, Puri N, Komath SS. Ras signaling activates glycosylphosphatidylinositol (GPI) anchor biosynthesis via the GPI- N-acetylglucosaminyltransferase (GPI-GnT) in Candida albicans. J Biol Chem 2018; 293:12222-12238. [PMID: 29907567 DOI: 10.1074/jbc.ra117.001225] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2017] [Revised: 04/17/2018] [Indexed: 01/08/2023] Open
Abstract
The ability of Candida albicans to switch between yeast to hyphal form is a property that is primarily associated with the invasion and virulence of this human pathogenic fungus. Several glycosylphosphatidylinositol (GPI)-anchored proteins are expressed only during hyphal morphogenesis. One of the major pathways that controls hyphal morphogenesis is the Ras-signaling pathway. We examine the cross-talk between GPI anchor biosynthesis and Ras signaling in C. albicans. We show that the first step of GPI biosynthesis is activated by Ras in C. albicans This is diametrically opposite to what is reported in Saccharomyces cerevisiae Of the two C. albicans Ras proteins, CaRas1 alone activates GPI-GnT activity; activity is further stimulated by constitutively activated CaRas1. CaRas1 localized to the cytoplasm or endoplasmic reticulum (ER) is sufficient for GPI-GnT activation. Of the six subunits of the GPI-N-acetylglucosaminyltransferase (GPI-GnT) that catalyze the first step of GPI biosynthesis, CaGpi2 is the key player involved in activating Ras signaling and hyphal morphogenesis. Activation of Ras signaling is independent of the catalytic competence of GPI-GnT. This too is unlike what is observed in S. cerevisiae where multiple subunits were identified as inhibiting Ras2. Fluorescence resonance energy transfer (FRET) studies indicate a specific physical interaction between CaRas1 and CaGpi2 in the ER, which would explain the ability of CaRas1 to activate GPI-GnT. CaGpi2, in turn, promotes activation of the Ras-signaling pathway and hyphal morphogenesis. The Cagpi2 mutant is also more susceptible to macrophage-mediated killing, and macrophage cells show better survival when co-cultured with Cagpi2.
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Affiliation(s)
- Priyanka Jain
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India
| | | | | | - Pramita Garai
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India
| | - Nilofer Naqvi
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India
| | - Sonali Singh
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India
| | - Kalpana Pawar
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India
| | - Niti Puri
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India
| | - Sneha Sudha Komath
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110 067, India.
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9
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A Lipid Transfer Protein Signaling Axis Exerts Dual Control of Cell-Cycle and Membrane Trafficking Systems. Dev Cell 2018; 44:378-391.e5. [PMID: 29396115 DOI: 10.1016/j.devcel.2017.12.026] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2016] [Revised: 09/24/2017] [Accepted: 12/28/2017] [Indexed: 11/21/2022]
Abstract
Kes1/Osh4 is a member of the conserved, but functionally enigmatic, oxysterol binding protein-related protein (ORP) superfamily that inhibits phosphatidylinositol transfer protein (Sec14)-dependent membrane trafficking through the trans-Golgi (TGN)/endosomal network. We now report that Kes1, and select other ORPs, execute cell-cycle control activities as functionally non-redundant inhibitors of the G1/S transition when cells confront nutrient-poor environments and promote replicative aging. Kes1-dependent cell-cycle regulation requires the Greatwall/MASTL kinase ortholog Rim15, and is opposed by Sec14 activity in a mechanism independent of Kes1/Sec14 bulk membrane-trafficking functions. Moreover, the data identify Kes1 as a non-histone target for NuA4 through which this lysine acetyltransferase co-modulates membrane-trafficking and cell-cycle activities. We propose the Sec14/Kes1 lipid-exchange protein pair constitutes part of the mechanism for integrating TGN/endosomal lipid signaling with cell-cycle progression and hypothesize that ORPs define a family of stage-specific cell-cycle control factors that execute tumor-suppressor-like functions.
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10
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Yadav A, Singh SL, Yadav B, Komath SS. Saccharomyces cerevisiae Gpi2, an accessory subunit of the enzyme catalyzing the first step of glycosylphosphatidylinositol (GPI) anchor biosynthesis, selectively complements some of the functions of its homolog in Candida albicans. Glycoconj J 2014; 31:497-507. [PMID: 25117514 DOI: 10.1007/s10719-014-9536-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2014] [Revised: 06/21/2014] [Accepted: 06/23/2014] [Indexed: 11/28/2022]
Abstract
GPI2 encodes for one of the six accessory subunits of the GPI-N-acetylglucosaminyltransferase (GPI-GnT) complex that catalyzes the first step of GPI biosynthesis in S. cerevisiae and C. albicans. It has been previously reported in S. cerevisiae that this subunit physically interacts with and negatively modulates Ras signaling. On the other hand, studies from our lab have shown that the homologous subunit in C. albicans is a positive modulator of Ras signaling. Are the functions of this subunit therefore strictly species dependent? We present here functional complementation studies on GPI2 from S. cerevisiae and C. albicans that were carried out to address this issue. Expression of CaGPI2 in a ScGPI2 conditional lethal mutant could not restore its growth defects. Likewise, ScGPI2 overexpression in a CaGPI2 heterozygous mutant could not restore its deficient GPI-GnT activity or reverse defects in its cell wall integrity and could only poorly restore filamentation. However, interestingly, ScGPI2 could restore lanosterol demethylase (CaERG11) levels and reverse azole resistance of the CaGPI2 heterozygote. It appeared to do this by regulating levels of another GPI-GnT subunit, CaGPI19, which we have previously shown to be involved in cross-talk with CaERG11. Thus, the effect of CaGPI2 on sterol biosynthesis in C. albicans is independent of its interaction with the GPI-GnT complex and Ras signaling pathways. In addition, the interaction of Gpi2 with other subunits of the GPI-GnT complex as well as with Ras signaling appears to have evolved differently in the two organisms.
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Affiliation(s)
- Anshuman Yadav
- Sneha Sudha Komath, School of Life Sciences, Jawaharlal Nehru University, New Delhi, 110067, India
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Comparative Analysis of Protein Glycosylation Pathways in Humans and the Fungal Pathogen Candida albicans. Int J Microbiol 2014; 2014:267497. [PMID: 25104959 PMCID: PMC4106090 DOI: 10.1155/2014/267497] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2014] [Accepted: 06/06/2014] [Indexed: 11/30/2022] Open
Abstract
Protein glycosylation pathways are present in all kingdoms of life and are metabolic pathways found in all the life kingdoms. Despite sharing commonalities in their synthesis, glycans attached to glycoproteins have species-specific structures generated by the presence of different sets of enzymes and acceptor substrates in each organism. In this review, we present a comparative analysis of the main glycosylation pathways shared by humans and the fungal pathogen Candida albicans: N-linked glycosylation, O-linked mannosylation and glycosylphosphatidylinositol-anchorage. The knowledge of similarities and divergences between these metabolic pathways could help find new pharmacological targets for C. albicans infection.
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12
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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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13
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Protein Glycosylation in Aspergillus fumigatus Is Essential for Cell Wall Synthesis and Serves as a Promising Model of Multicellular Eukaryotic Development. Int J Microbiol 2011; 2012:654251. [PMID: 21977037 PMCID: PMC3184424 DOI: 10.1155/2012/654251] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2011] [Accepted: 07/19/2011] [Indexed: 02/05/2023] Open
Abstract
Glycosylation is a conserved posttranslational modification that is found in all eukaryotes, which helps generate proteins with multiple functions. Our knowledge of glycosylation mainly comes from the investigation of the yeast Saccharomyces cerevisiae and mammalian cells. However, during the last decade, glycosylation in the human pathogenic mold Aspergillus fumigatus has drawn significant attention. It has been revealed that glycosylation in A. fumigatus is crucial for its growth, cell wall synthesis, and development and that the process is more complicated than that found in the budding yeast S. cerevisiae. The present paper implies that the investigation of glycosylation in A. fumigatus is not only vital for elucidating the mechanism of fungal cell wall synthesis, which will benefit the design of new antifungal therapies, but also helps to understand the role of protein glycosylation in the development of multicellular eukaryotes. This paper describes the advances in functional analysis of protein glycosylation in A. fumigatus.
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Victoria GS, Kumar P, Komath SS. The Candida albicans homologue of PIG-P, CaGpi19p: gene dosage and role in growth and filamentation. Microbiology (Reading) 2010; 156:3041-3051. [DOI: 10.1099/mic.0.039628-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Glycosylphosphatidyl inositol (GPI)-anchored proteins in Candida albicans are responsible for a vast range of functions, and deletions in certain GPI-anchored proteins severely reduce adhesion and virulence of this organism. In addition, completely modified GPIs are necessary for virulence. GPI anchor biosynthesis is essential for viability and starts with the transfer of N-acetylglucosamine to phosphatidylinositol. This step is catalysed by a multi-subunit complex, GPI–N-acetylglucosaminyltransferase (GPI–GnT). In this, the first report to our knowledge on a subunit of the Candida GPI–GnT complex, we show that CaGpi19p is the functional equivalent of the Saccharomyces cerevisiae Gpi19p. An N-terminal truncation mutant of CaGpi19p functionally complements a conditionally lethal S. cerevisiae gpi19 mutant. Further, we constructed a conditional null mutant of CaGPI19 by disrupting one allele and placing the remaining copy under the control of the MET3 promoter. Repression leads to growth defects, cell wall biogenesis aberrations, azole sensitivity and hyperfilamention. In addition, there is a noticeable gene dosage effect, with the heterozygote also displaying intermediate degrees of most phenotypes. The mutants also displayed a reduced susceptibility to the antifungal agent amphotericin B. Collectively, the results suggest that CaGPI19 is required for normal morphology and cell wall architecture.
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Affiliation(s)
| | - Pravin Kumar
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
| | - Sneha Sudha Komath
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
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15
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Beese SE, Negishi T, Levin DE. Identification of positive regulators of the yeast fps1 glycerol channel. PLoS Genet 2009; 5:e1000738. [PMID: 19956799 PMCID: PMC2773846 DOI: 10.1371/journal.pgen.1000738] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2009] [Accepted: 10/23/2009] [Indexed: 11/18/2022] Open
Abstract
The yeast Fps1 protein is an aquaglyceroporin that functions as the major facilitator of glycerol transport in response to changes in extracellular osmolarity. Although the High Osmolarity Glycerol pathway is thought to have a function in at least basal control of Fps1 activity, its mode of regulation is not understood. We describe the identification of a pair of positive regulators of the Fps1 glycerol channel, Rgc1 (Ypr115w) and Rgc2 (Ask10). An rgc1/2Δ mutant experiences cell wall stress that results from osmotic pressure associated with hyper-accumulation of glycerol. Accumulation of glycerol in the rgc1/2Δ mutant results from a defect in Fps1 activity as evidenced by suppression of the defect through Fps1 overexpression, failure to release glycerol upon hypo-osmotic shock, and resistance to arsenite, a toxic metalloid that enters the cell through Fps1. Regulation of Fps1 by Rgc1/2 appears to be indirect; however, evidence is presented supporting the view that Rgc1/2 regulate Fps1 channel activity, rather than its expression, folding, or localization. Rgc2 was phosphorylated in response to stresses that lead to regulation of Fps1. This stress-induced phosphorylation was partially dependent on the Hog1 MAPK. Hog1 was also required for basal phosphorylation of Rgc2, suggesting a mechanism by which Hog1 may regulate Fps1 indirectly. When challenged by changes in extracellular osmolarity, many fungal species regulate their intracellular glycerol concentration to modulate their internal osmotic pressure. Maintenance of osmotic homeostasis prevents either cellular collapse under hyper-osmotic stress or cell rupture under hypo-osmotic stress. In baker's yeast, the Fps1 glycerol channel functions as the main vent for glycerol. Proper regulation of Fps1 is critical to the maintenance of osmotic homeostasis. In this study, we identify a pair of proteins (Rgc1 and Rgc2) that function as positive regulators of Fps1 activity. Their absence results in hyper-accumulation of glycerol and consequent cell lysis due to impaired Fps1 channel activity. Additionally, we found that these glycerol channel regulators function between the Hog1 (High Osmolarity Glycerol response) signaling kinase and Fps1, defining a signaling pathway for control of glycerol efflux. Because members of the Rgc1/2 family are found among pathogenic fungal species, but not in humans, they represent potentially attractive targets for antifungal drug development.
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Affiliation(s)
- Sara E. Beese
- Department of Biochemistry and Molecular Biology, Bloomberg School of Public Health, The Johns Hopkins University, Baltimore, Maryland, United States of America
| | - Takahiro Negishi
- Department of Biochemistry and Molecular Biology, Bloomberg School of Public Health, The Johns Hopkins University, Baltimore, Maryland, United States of America
| | - David E. Levin
- Department of Biochemistry and Molecular Biology, Bloomberg School of Public Health, The Johns Hopkins University, Baltimore, Maryland, United States of America
- Department of Molecular and Cell Biology, Boston University Goldman School of Dental Medicine, Boston, Massachusetts, United States of America
- * E-mail:
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16
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The Aspergillus nidulans pigP gene encodes a subunit of GPI-N-acetylglucosaminyltransferase which influences filamentation and protein secretion. Curr Genet 2009; 55:301-9. [PMID: 19421754 DOI: 10.1007/s00294-009-0246-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2009] [Revised: 04/16/2009] [Accepted: 04/19/2009] [Indexed: 10/20/2022]
Abstract
Glycosylphosphatidylinositol (GPI) anchoring is the main mechanism allowing proper localization of secretory proteins in cell membranes. We have isolated an Aspergillus nidulans homolog of the human PIG-P gene, which encodes a subunit of acetylglucosaminyltransferase (GPI-GnT)-an enzyme involved in the synthesis of GPI anchors. A. nidulans pigP mutants have significantly decreased GPI synthesis. On solid media they show strong growth retardation (the "button" phenotype) while in liquid minimal media they show overall good growth but with hyperbranched and bulbous hyphae with impaired septation. Furthermore, the pigP strains, in contrast to the wild-type, abundantly secrete a 33-kDa alkaline serine protease (ALP) into the liquid medium.
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17
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Chapter 1 Overview of GPI Biosynthesis. ACTA ACUST UNITED AC 2009. [DOI: 10.1016/s1874-6047(09)26001-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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18
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Remy E, Meyer M, Blaise F, Simon UK, Kuhn D, Chabirand M, Riquelme M, Balesdent MH, Rouxel T. The Lmgpi15 gene, encoding a component of the glycosylphosphatidylinositol anchor biosynthesis pathway, is required for morphogenesis and pathogenicity in Leptosphaeria maculans. THE NEW PHYTOLOGIST 2008; 179:1105-1120. [PMID: 18557818 DOI: 10.1111/j.1469-8137.2008.02522.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Random insertional mutagenesis was used to investigate pathogenicity determinants in Leptosphaeria maculans. One tagged nonpathogenic mutant, termed m20, was analysed in detail here. The mutant phenotype was investigated by microscopic analyses of infected plant tissues and in vitro growth assays. Complementation and silencing experiments were used to identify the altered gene. Its function was determined by bioinformatics analyses, cell biology experiments and functional studies. The mutant was blocked at the invasive growth phase after an unaffected initial penetration stage, and displayed a reduced growth rate and an aberrant hyphal morphology in vitro. The T-DNA insertion occurred in the intergenic region between two head-to-tail genes, leading to a complex deregulation of their expression. The unique gene accounting for the mutant phenotype was suggested to be the orthologue of the poorly conserved Saccharomyces cerevisiae gpi15, which encodes for one component of the glycosylphosphatidylinositol (GPI) anchor biosynthesis pathway. Consistent with this predicted function, a functional translational fusion with the green fluorescent protein (GFP) was targeted to the endoplasmic reticulum. Moreover, the mutant exhibited an altered cell wall and addition of glucosamine relieved growth defects. It is concluded that the GPI anchor biosynthetic pathway is required for morphogenesis, cell wall integrity and pathogenicity in Leptosphaeria maculans.
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Affiliation(s)
- Estelle Remy
- INRA, UMR 1290 BIOGER, Route de Saint-Cyr, F-78026 Versailles Cedex, France
| | - Michel Meyer
- INRA, UMR 1290 BIOGER, Route de Saint-Cyr, F-78026 Versailles Cedex, France
| | - Françoise Blaise
- INRA, UMR 1290 BIOGER, Route de Saint-Cyr, F-78026 Versailles Cedex, France
| | - Uwe K Simon
- Lehrstuhl Spezielle Botanik und Mykologie, Universität Tübingen, Auf der Morgenstelle 1, 72076 Tübingen, Germany
| | - Diana Kuhn
- Lehrstuhl Spezielle Botanik und Mykologie, Universität Tübingen, Auf der Morgenstelle 1, 72076 Tübingen, Germany
| | - Mélanie Chabirand
- INRA, UMR 1290 BIOGER, Route de Saint-Cyr, F-78026 Versailles Cedex, France
| | - Meritxell Riquelme
- Centro de Investigación Científica y de Educación Superior de Ensenada, Departamento de Microbiología, Edificio DBEA, Km. 107 Ctra. Tijuana-Ensenada, 22860 Ensenada, Baja California, Mexico
| | | | - Thierry Rouxel
- INRA, UMR 1290 BIOGER, Route de Saint-Cyr, F-78026 Versailles Cedex, France
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Santos A, San Mauro M, Abrusci C, Marquina D. Cwp2p, the plasma membrane receptor for Pichia membranifaciens killer toxin. Mol Microbiol 2007; 64:831-43. [PMID: 17462027 DOI: 10.1111/j.1365-2958.2007.05702.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
PMKT is a channel-forming killer toxin secreted by Pichia membranifaciens. To identify novel genes that mediate cellular resistance to PMKT we screened a collection of 288 deletion mutants. We found 29 open reading frames (ORFs) that, when deleted, confer resistance to PMKT. In addition, the deletion of 15 ORFs was observed to increase protoplast resistance, in agreement with the initial assumption that a plasma membrane receptor for PMKT exists. Whole cells and protoplasts of a cwp2Delta mutant were found to be completely resistant to PMKT and were unable to bind PMKT, indicating that Cwp2p interacts with it. A protein with a molecular mass of 11.7 kDa was purified from PMKT-affinity columns. This protein was sequenced and identified as Cwp2p. Glycosylphosphatidylinositol (GPI) anchoring-defective mutants were much less sensitive to PMKT, as were wild-type protoplasts pretreated with phosphatidylinositol-specific phospholipase C to remove GPI-anchored proteins, indicating that the GPI-anchored precursor of Cwp2p is also necessary for PMKT activity. Carboxyfluorescein-entrapped liposomes containing a purified GFP-Cwp2p fusion protein in their membranes were much more sensitive to PMKT than protein-free liposomes. Cwp2p and its GPI-anchored precursor are proposed for the first time to be involved as PMKT secondary receptors.
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Affiliation(s)
- Antonio Santos
- Department of Microbiology, Biology Faculty, Complutense University of Madrid, 28040 Madrid, Spain
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20
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Li H, Zhou H, Luo Y, Ouyang H, Hu H, Jin C. Glycosylphosphatidylinositol (GPI) anchor is required in Aspergillus fumigatus for morphogenesis and virulence. Mol Microbiol 2007; 64:1014-27. [PMID: 17501924 DOI: 10.1111/j.1365-2958.2007.05709.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
In yeast, glycosylphosphatidylinositol (GPI) is essential for viability and plays an important role in biosynthesis and organization of cell wall. Initiation of the GPI anchor biosynthesis is catalysed by the GPI-N-acetylglucosaminyltransferase complex (GPI-GnT). The GPI3 (SPT14) gene is thought to encode the catalytic subunit of GPI-GnT complex. In contrast to Saccharomyces cerevisiae, little is known about the GPI biosynthesis in filamentous fungi. In this study, the afpig-a gene was identified as the homologue of the GPI3/pig-A gene in Aspergillus fumigatus, an opportunistic fungal pathogen. By replacement of the afpig-a gene with a pyrG gene, we obtained the null mutants. Although the Deltaafpig-a mutant exhibited a significant increased cell lysis instead of temperature-sensitive or conditional lethal phenotype associated to the GPI3 mutant of yeast, they could survive at temperatures from 30 degrees C to 50 degrees C. The analysis of the mutants showed that a completely blocking of the GPI anchor synthesis in A. fumigatus led to cell wall defect, abnormal hyphal growth, rapid conidial germination and aberrant conidiation. In vivo assays revealed that the mutant exhibited a reduced virulence in immunocompromised mice. The GPI anchor was not essential for viability, but required for the cell wall integrity, morphogenesis and virulence in A. fumigatus.
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Affiliation(s)
- Hong Li
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, and The General Hospital of Chinese People's Armed Police Forces, Beijing 100080, China
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21
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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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22
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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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23
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Current awareness on yeast. Yeast 2006. [DOI: 10.1002/yea.1315] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
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