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Mohorko E, Glockshuber R, Aebi M. Oligosaccharyltransferase: the central enzyme of N-linked protein glycosylation. J Inherit Metab Dis 2011; 34:869-78. [PMID: 21614585 DOI: 10.1007/s10545-011-9337-1] [Citation(s) in RCA: 155] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/17/2010] [Revised: 04/01/2011] [Accepted: 04/07/2011] [Indexed: 01/07/2023]
Abstract
N-linked glycosylation is one of the most abundant modifications of proteins in eukaryotic organisms. In the central reaction of the pathway, oligosaccharyltransferase (OST), a multimeric complex located at the membrane of the endoplasmic reticulum, transfers a preassembled oligosaccharide to selected asparagine residues within the consensus sequence asparagine-X-serine/threonine. Due to the high substrate specificity of OST, alterations in the biosynthesis of the oligosaccharide substrate result in the hypoglycosylation of many different proteins and a multitude of symptoms observed in the family of congenital disorders of glycosylation (CDG) type I. This review covers our knowledge of human OST and describes enzyme composition. The Stt3 subunit of OST harbors the catalytic center of the enzyme, but the function of the other, highly conserved, subunits are less well defined. Some components seem to be involved in the recognition and utilization of glycosylation sites in specific glycoproteins. Indeed, mutations in the subunit paralogs N33/Tusc3 and IAP do not yield the pleiotropic phenotypes typical for CDG type I but specifically result in nonsyndromic mental retardation, suggesting that the oxidoreductase activity of these subunits is required for glycosylation of a subset of proteins essential for brain development.
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Wohlschlager T, Butschi A, Zurfluh K, Vonesch SC, Auf dem Keller U, Gehrig P, Bleuler-Martinez S, Hengartner MO, Aebi M, Künzler M. Nematotoxicity of Marasmius oreades agglutinin (MOA) depends on glycolipid binding and cysteine protease activity. J Biol Chem 2011; 286:30337-30343. [PMID: 21757752 DOI: 10.1074/jbc.m111.258202] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Fruiting body lectins have been proposed to act as effector proteins in the defense of fungi against parasites and predators. The Marasmius oreades agglutinin (MOA) is a Galα1,3Gal/GalNAc-specific lectin from the fairy ring mushroom that consists of an N-terminal ricin B-type lectin domain and a C-terminal dimerization domain. The latter domain shows structural similarity to catalytically active proteins, suggesting that, in addition to its carbohydrate-binding activity, MOA has an enzymatic function. Here, we demonstrate toxicity of MOA toward the model nematode Caenorhabditis elegans. This toxicity depends on binding of MOA to glycosphingolipids of the worm via its lectin domain. We show further that MOA has cysteine protease activity and demonstrate a critical role of this catalytic function in MOA-mediated nematotoxicity. The proteolytic activity of MOA was dependent on high Ca(2+) concentrations and favored by slightly alkaline pH, suggesting that these conditions trigger activation of the toxin at the target location. Our results suggest that MOA is a fungal toxin with intriguing similarities to bacterial binary toxins and has a protective function against fungivorous soil nematodes.
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78
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Lizak C, Gerber S, Numao S, Aebi M, Locher KP. X-ray structure of a bacterial oligosaccharyltransferase. Nature 2011; 474:350-5. [PMID: 21677752 DOI: 10.1038/nature10151] [Citation(s) in RCA: 285] [Impact Index Per Article: 21.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2011] [Accepted: 04/26/2011] [Indexed: 12/25/2022]
Abstract
Asparagine-linked glycosylation is a post-translational modification of proteins containing the conserved sequence motif Asn-X-Ser/Thr. The attachment of oligosaccharides is implicated in diverse processes such as protein folding and quality control, organism development or host-pathogen interactions. The reaction is catalysed by oligosaccharyltransferase (OST), a membrane protein complex located in the endoplasmic reticulum. The central, catalytic enzyme of OST is the STT3 subunit, which has homologues in bacteria and archaea. Here we report the X-ray structure of a bacterial OST, the PglB protein of Campylobacter lari, in complex with an acceptor peptide. The structure defines the fold of STT3 proteins and provides insight into glycosylation sequon recognition and amide nitrogen activation, both of which are prerequisites for the formation of the N-glycosidic linkage. We also identified and validated catalytically important, acidic amino acid residues. Our results provide the molecular basis for understanding the mechanism of N-linked glycosylation.
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Bleuler-Martínez S, Butschi A, Garbani M, Wälti MA, Wohlschlager T, Potthoff E, Sabotiĉ J, Pohleven J, Lüthy P, Hengartner MO, Aebi M, Künzler M. A lectin-mediated resistance of higher fungi against predators and parasites. Mol Ecol 2011; 20:3056-70. [PMID: 21486374 DOI: 10.1111/j.1365-294x.2011.05093.x] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Fruiting body lectins are ubiquitous in higher fungi and characterized by being synthesized in the cytoplasm and up-regulated during sexual development. The function of these lectins is unclear. A lack of phenotype in sexual development upon inactivation of the respective genes argues against a function in this process. We tested a series of characterized fruiting body lectins from different fungi for toxicity towards the nematode Caenorhabditis elegans, the mosquito Aedes aegypti and the amoeba Acanthamoeba castellanii. Most of the fungal lectins were found to be toxic towards at least one of the three target organisms. By altering either the fungal lectin or the glycans of the target organisms, or by including soluble carbohydrate ligands as competitors, we demonstrate that the observed toxicity is dependent on the interaction between the fungal lectins and specific glycans in the target organisms. The toxicity was found to be dose-dependent such that low levels of lectin were no longer toxic but still led to food avoidance by C. elegans. Finally, we show, in an ecologically more relevant scenario, that challenging the vegetative mycelium of Coprinopsis cinerea with the fungal-feeding nematode Aphelenchus avenae induces the expression of the nematotoxic fruiting body lectins CGL1 and CGL2. Based on these findings, we propose that filamentous fungi possess an inducible resistance against predators and parasites mediated by lectins that are specific for glycans of these antagonists.
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80
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Ragni E, Piberger H, Neupert C, García-Cantalejo J, Popolo L, Arroyo J, Aebi M, Strahl S. The genetic interaction network of CCW12, a Saccharomyces cerevisiae gene required for cell wall integrity during budding and formation of mating projections. BMC Genomics 2011; 12:107. [PMID: 21320323 PMCID: PMC3049148 DOI: 10.1186/1471-2164-12-107] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2010] [Accepted: 02/14/2011] [Indexed: 01/19/2023] Open
Abstract
Background Mannoproteins construct the outer cover of the fungal cell wall. The covalently linked cell wall protein Ccw12p is an abundant mannoprotein. It is considered as crucial structural cell wall component since in baker's yeast the lack of CCW12 results in severe cell wall damage and reduced mating efficiency. Results In order to explore the function of CCW12, we performed a Synthetic Genetic Analysis (SGA) and identified genes that are essential in the absence of CCW12. The resulting interaction network identified 21 genes involved in cell wall integrity, chitin synthesis, cell polarity, vesicular transport and endocytosis. Among those are PFD1, WHI3, SRN2, PAC10, FEN1 and YDR417C, which have not been related to cell wall integrity before. We correlated our results with genetic interaction networks of genes involved in glucan and chitin synthesis. A core of genes essential to maintain cell integrity in response to cell wall stress was identified. In addition, we performed a large-scale transcriptional analysis and compared the transcriptional changes observed in mutant ccw12Δ with transcriptomes from studies investigating responses to constitutive or acute cell wall damage. We identified a set of genes that are highly induced in the majority of the mutants/conditions and are directly related to the cell wall integrity pathway and cell wall compensatory responses. Among those are BCK1, CHS3, EDE1, PFD1, SLT2 and SLA1 that were also identified in the SGA. In contrast, a specific feature of mutant ccw12Δ is the transcriptional repression of genes involved in mating. Physiological experiments substantiate this finding. Further, we demonstrate that Ccw12p is present at the cell periphery and highly concentrated at the presumptive budding site, around the bud, at the septum and at the tip of the mating projection. Conclusions The combination of high throughput screenings, phenotypic analyses and localization studies provides new insight into the function of Ccw12p. A compensatory response, culminating in cell wall remodelling and transport/recycling pathways is required to buffer the loss of CCW12. Moreover, the enrichment of Ccw12p in bud, septum and mating projection is consistent with a role of Ccw12p in preserving cell wall integrity at sites of active growth. The microarray data produced in this analysis have been submitted to NCBI GEO database and GSE22649 record was assigned.
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81
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Lizak C, Fan YY, Weber TC, Aebi M. N-Linked Glycosylation of Antibody Fragments in Escherichia coli. Bioconjug Chem 2011; 22:488-96. [DOI: 10.1021/bc100511k] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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82
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Yavuz E, Maffioli C, Ilg K, Aebi M, Priem B. Glycomimicry: display of fucosylation on the lipo-oligosaccharide of recombinant Escherichia coli K12. Glycoconj J 2011; 28:39-47. [PMID: 21286806 DOI: 10.1007/s10719-010-9322-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2010] [Revised: 12/06/2010] [Accepted: 12/21/2010] [Indexed: 10/18/2022]
Abstract
We recently described the design of Escherichia coli K12 and Salmonella enterica sv Typhimurium to display the gangliomannoside 3 (GM3) antigen on the cell surface. We report here the fucosylation of modified lipooligosaccharide in a recombinant E.coli strain with a truncated lipid A core due to deletion of the core glycosyltransferases genes waaO and waaB. This truncated structure was used as a scaffold to assemble the Lewis Y motif by consequent action of the heterologously expressed β-1,4 galactosyltransferase LgtE (Neisseria gonorrheae), the β-1,3 N-acetylglucosaminyltransferase LgtA and the β-1,3 galactosyltransferase LgtB from Neisseria meningitidis, as well as the α-1,2 and α-1,3 fucosyltransferases FutC and FutA from Helicobacter pylori. We show the display of the Lewis Y structure by immunological and chemical analysis.
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83
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Aebi M, Müller UC, Asherson P, Banaschewski T, Buitelaar J, Ebstein R, Eisenberg J, Gill M, Manor I, Miranda A, Oades RD, Roeyers H, Rothenberger A, Sergeant J, Sonuga-Barke E, Thompson M, Taylor E, Faraone SV, Steinhausen HC. Predictability of oppositional defiant disorder and symptom dimensions in children and adolescents with ADHD combined type. Psychol Med 2010; 40:2089-2100. [PMID: 20380783 DOI: 10.1017/s0033291710000590] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
BACKGROUND Oppositional defiant disorder (ODD) is frequently co-occurring with attention deficit hyperactivity disorder (ADHD) in children and adolescents. Because ODD is a precursor of later conduct disorder (CD) and affective disorders, early diagnostic identification is warranted. Furthermore, the predictability of three recently confirmed ODD dimensions (ODD-irritable, ODD-headstrong and ODD-hurtful) may assist clinical decision making. METHOD Receiver-operating characteristic (ROC) analysis was used in order to test the diagnostic accuracy of the Conners' Parent Rating Scale revised (CPRS-R) and the parent version of the Strength and Difficulties Questionnaire (PSDQ) in the prediction of ODD in a transnational sample of 1093 subjects aged 5-17 years from the International Multicentre ADHD Genetics study. In a second step, the prediction of three ODD dimensions by the same parent rating scales was assessed by backward linear regression analyses. RESULTS ROC analyses showed adequate diagnostic accuracy of the CPRS-R and the PSDQ in predicting ODD in this ADHD sample. Furthermore, the three-dimensional structure of ODD was confirmed by confirmatory factor analysis and the CPRS-R emotional lability scale significantly predicted the ODD irritable dimension. CONCLUSIONS The PSDQ and the CPRS-R are both suitable screening instruments in the identification of ODD. The emotional lability scale of the CPRS-R is an adequate predictor of irritability in youth referred for ADHD.
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84
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Schwarz F, Lizak C, Fan YY, Fleurkens S, Kowarik M, Aebi M. Relaxed acceptor site specificity of bacterial oligosaccharyltransferase in vivo. Glycobiology 2010; 21:45-54. [DOI: 10.1093/glycob/cwq130] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
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85
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Dürr C, Nothaft H, Lizak C, Glockshuber R, Aebi M. The Escherichia coli glycophage display system. Glycobiology 2010; 20:1366-72. [PMID: 20581006 DOI: 10.1093/glycob/cwq102] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
We describe a phage display technique that allows the production and selective enrichment of phages that display an N-glycoprotein (glycophages). We applied glycophage display to select functional glycosylation sequons from a pool of randomized acceptor sequences. Our system provides a genetic platform to study and engineer different steps in the pathway of bacterial N-linked protein glycosylation.
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86
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Ilg K, Yavuz E, Maffioli C, Priem B, Aebi M. Glycomimicry: Display of the GM3 sugar epitope on Escherichia coli and Salmonella enterica sv Typhimurium. Glycobiology 2010; 20:1289-97. [DOI: 10.1093/glycob/cwq091] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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87
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Schwarz F, Huang W, Li C, Schulz BL, Lizak C, Palumbo A, Numao S, Neri D, Aebi M, Wang LX. A combined method for producing homogeneous glycoproteins with eukaryotic N-glycosylation. Nat Chem Biol 2010; 6:264-6. [PMID: 20190762 PMCID: PMC2842479 DOI: 10.1038/nchembio.314] [Citation(s) in RCA: 138] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2009] [Accepted: 12/29/2009] [Indexed: 11/09/2022]
Abstract
We describe a novel method for producing homogeneous eukaryotic N-glycoproteins. The method involves the engineering and functional transfer of the C. jejuni glycosylation machinery in E. coli to express glycosylated proteins with the key GlcNAc-Asn linkage. The bacterial glycans were then trimmed and remodeled in vitro by enzymatic transglycosylation to fulfill a eukaryotic N-glycosylation. It provides a potentially general platform for producing eukaryotic N-glycoproteins.
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88
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Marchesi DG, Boos N, Zuber K, Aebi M. Translaminar facet joint screws to enhance segmental fusion of the lumbar spine. EUROPEAN SPINE JOURNAL : OFFICIAL PUBLICATION OF THE EUROPEAN SPINE SOCIETY, THE EUROPEAN SPINAL DEFORMITY SOCIETY, AND THE EUROPEAN SECTION OF THE CERVICAL SPINE RESEARCH SOCIETY 2010; 1:125-30. [PMID: 20054959 DOI: 10.1007/bf00300939] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
From 1984 to 1988, 70 consecutive lumbar and lumbosacral spine fusions enhanced with translaminar facet joint screws were performed for segmental degenerative disease. Twenty patients had partial decompression of central stenosis, 15 concomitant discectomy, and 19 lateral nerve root decompression. The mean time to fusion was 4.5 months (range 2-7 months). At followup (average 45 months; range 24-74 months) 98.5% were judged to have solid fusion. Satisfactory results were observed in 84% of cases, 91% without previous surgery and 75% after previous discectomy. Supplementation of posterolateral fusion by translaminar facet screws significantly improved time to fusion, fusion rate, and clinical outcomes with no significant increased complications.
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89
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Buser R, Lazar Z, Käser S, Künzler M, Aebi M. Identification, characterization, and biosynthesis of a novel N-glycan modification in the fruiting body of the basidiomycete Coprinopsis cinerea. J Biol Chem 2010; 285:10715-23. [PMID: 20061575 DOI: 10.1074/jbc.m109.076075] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Coprinopsis cinerea is a model organism for fruiting body development in homobasidiomycetes. Here, we focused on N-linked oligosaccharides (NLO) of cell wall proteins in the hyphae of two developmental stages, vegetative mycelium and fruiting body. High mannose-type glycans were the most commonly found structures. In addition, we observed a novel glycan, predominantly present in fruiting body. This oligosaccharide structure was of the high mannose type with at least five mannoses and a bisecting alpha1-4 N-acetylglucosamine (GlcNAc) at the beta-mannose of the N-glycan core. The transferase responsible for this modification, CcGnt1 (C. cinerea GlcNAc transferase 1), was identified and expressed in insect cells. In vitro activity of CcGnt1 was demonstrated. This novel glycosyltransferase belongs to the glycosyltransferase family 8 (GT8) and is predicted to be a type II membrane protein. Expression of the CcGnt1 locus was up-regulated in fruiting body, but down-regulation of expression by means of RNAi decreased the level of bisected NLO; however had no apparent effect on fruiting body formation.
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90
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Kuhn C, Winkler Metzke C, Aebi M, Steinhausen HC. PW01-59 - Effects of an internet based assessment of child and adolescent psychopathology (DAWBA) on clinical decision making. Eur Psychiatry 2010. [DOI: 10.1016/s0924-9338(10)71458-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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91
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Aebi M, Bessler C. P02-47 - Juvenile sex offenders in Switzerland: demographic factors, psychopathology, offence characteristics and recidivism. Eur Psychiatry 2010. [DOI: 10.1016/s0924-9338(10)70661-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/19/2022] Open
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92
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Butschi A, Titz A, Wälti MA, Olieric V, Paschinger K, Nöbauer K, Guo X, Seeberger PH, Wilson IBH, Aebi M, Hengartner MO, Künzler M. Caenorhabditis elegans N-glycan core beta-galactoside confers sensitivity towards nematotoxic fungal galectin CGL2. PLoS Pathog 2010; 6:e1000717. [PMID: 20062796 PMCID: PMC2798750 DOI: 10.1371/journal.ppat.1000717] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2009] [Accepted: 12/04/2009] [Indexed: 12/01/2022] Open
Abstract
The physiological role of fungal galectins has remained elusive. Here, we show that feeding of a mushroom galectin, Coprinopsis cinerea CGL2, to Caenorhabditis elegans inhibited development and reproduction and ultimately resulted in killing of this nematode. The lack of toxicity of a carbohydrate-binding defective CGL2 variant and the resistance of a C. elegans mutant defective in GDP-fucose biosynthesis suggested that CGL2-mediated nematotoxicity depends on the interaction between the galectin and a fucose-containing glycoconjugate. A screen for CGL2-resistant worm mutants identified this glycoconjugate as a Galbeta1,4Fucalpha1,6 modification of C. elegans N-glycan cores. Analysis of N-glycan structures in wild type and CGL2-resistant nematodes confirmed this finding and allowed the identification of a novel putative glycosyltransferase required for the biosynthesis of this glycoepitope. The X-ray crystal structure of a complex between CGL2 and the Galbeta1,4Fucalpha1,6GlcNAc trisaccharide at 1.5 A resolution revealed the biophysical basis for this interaction. Our results suggest that fungal galectins play a role in the defense of fungi against predators by binding to specific glycoconjugates of these organisms.
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93
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Titz A, Butschi A, Henrissat B, Fan YY, Hennet T, Razzazi-Fazeli E, Hengartner MO, Wilson IBH, Künzler M, Aebi M. Molecular basis for galactosylation of core fucose residues in invertebrates: identification of caenorhabditis elegans N-glycan core alpha1,6-fucoside beta1,4-galactosyltransferase GALT-1 as a member of a novel glycosyltransferase family. J Biol Chem 2009; 284:36223-36233. [PMID: 19858195 DOI: 10.1074/jbc.m109.058354] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Galectin CGL2 from the ink cap mushroom Coprinopsis cinerea displays toxicity toward the model nematode Caenorhabditis elegans. A mutation in a putative glycosyltransferase-encoding gene resulted in a CGL2-resistant C. elegans strain characterized by N-glycans lacking the beta1,4-galactoside linked to the alpha1,6-linked core fucose. Expression of the corresponding GALT-1 protein in insect cells was used to demonstrate a manganese-dependent galactosyltransferase activity. In vitro, the GALT-1 enzyme showed strong selectivity for acceptors with alpha1,6-linked N-glycan core fucosides and required Golgi- dependent modifications on the oligosaccharide antennae for optimal synthesis of the Gal-beta1,4-fucose structure. Phylogenetic analysis of the GALT-1 protein sequence identified a novel glycosyltransferase family (GT92) with members widespread among eukarya but absent in mammals.
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94
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Aebi M, Bernasconi R, Clerc S, Molinari M. N-glycan structures: recognition and processing in the ER. Trends Biochem Sci 2009; 35:74-82. [PMID: 19853458 DOI: 10.1016/j.tibs.2009.10.001] [Citation(s) in RCA: 339] [Impact Index Per Article: 22.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2009] [Revised: 09/30/2009] [Accepted: 10/01/2009] [Indexed: 11/26/2022]
Abstract
The processing of N-linked glycans determines secretory protein homeostasis in the eukaryotic cell. Folding and degradation of glycoproteins in the endoplasmic reticulum (ER) are regulated by molecular chaperones and enzymes recruited by specific oligosaccharide structures. Recent findings have identified several components of this protein quality control system that specifically modify N-linked glycans, thereby generating oligosaccharide structures recognized by carbohydrate-binding proteins, lectins. In turn, lectins direct newly synthesized polypeptides to the folding, secretion or degradation pathways. The "glyco-code of the ER" displays the folding status of a multitude of cargo proteins. Deciphering this code will be instrumental in understanding protein homeostasis regulation in eukaryotic cells and for intervention because such processes can have crucial importance for clinical and industrial applications.
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Izquierdo L, Schulz BL, Rodrigues JA, Güther MLS, Procter JB, Barton GJ, Aebi M, Ferguson MAJ. Distinct donor and acceptor specificities of Trypanosoma brucei oligosaccharyltransferases. EMBO J 2009; 28:2650-61. [PMID: 19629045 PMCID: PMC2722254 DOI: 10.1038/emboj.2009.203] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2009] [Accepted: 06/18/2009] [Indexed: 11/09/2022] Open
Abstract
Asparagine-linked glycosylation is catalysed by oligosaccharyltransferase (OTase). In Trypanosoma brucei OTase activity is catalysed by single-subunit enzymes encoded by three paralogous genes of which TbSTT3B and TbSTT3C can complement a yeast Δstt3 mutant. The two enzymes have overlapping but distinct peptide acceptor specificities, with TbSTT3C displaying an enhanced ability to glycosylate sites flanked by acidic residues. TbSTT3A and TbSTT3B, but not TbSTT3C, are transcribed in the bloodstream and procyclic life cycle stages of T. brucei. Selective knockdown and analysis of parasite protein N-glycosylation showed that TbSTT3A selectively transfers biantennary Man5GlcNAc2 to specific glycosylation sites whereas TbSTT3B selectively transfers triantennary Man9GlcNAc2 to others. Analysis of T. brucei glycosylation site occupancy showed that TbSTT3A and TbSTT3B glycosylate sites in acidic to neutral and neutral to basic regions of polypeptide, respectively. This embodiment of distinct specificities in single-subunit OTases may have implications for recombinant glycoprotein engineering. TbSTT3A and TbSTT3B could be knocked down individually, but not collectively, in tissue culture. However, both were independently essential for parasite growth in mice, suggesting that inhibiting protein N-glycosylation could have therapeutic potential against trypanosomiasis.
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96
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Röder C, Staub L, Dietrich D, Zweig T, Melloh M, Aebi M. Benchmarking with Spine Tango: potentials and pitfalls. EUROPEAN SPINE JOURNAL : OFFICIAL PUBLICATION OF THE EUROPEAN SPINE SOCIETY, THE EUROPEAN SPINAL DEFORMITY SOCIETY, AND THE EUROPEAN SECTION OF THE CERVICAL SPINE RESEARCH SOCIETY 2009; 18 Suppl 3:305-11. [PMID: 19337759 DOI: 10.1007/s00586-009-0943-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2008] [Revised: 03/11/2009] [Accepted: 03/12/2009] [Indexed: 12/01/2022]
Abstract
The newly released online statistics function of Spine Tango allows comparison of own data against the aggregated results of the data pool that all other participants generate. This comparison can be considered a very simple way of benchmarking, which means that the quality of what one organization does is compared with other similar organizations. The goal is to make changes towards better practice if benchmarking shows inferior results compared with the pool. There are, however, pitfalls in this simplified way of comparing data that can result in confounding. This means that important influential factors can make results appear better or worse than they are in reality and these factors can only be identified and neutralized in a multiple regression analysis performed by a statistical expert. Comparing input variables, confounding is less of a problem than comparing outcome variables. Therefore, the potentials and limitations of automated online comparisons need to be considered when interpreting the results of the benchmarking procedure.
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Clerc S, Hirsch C, Oggier DM, Deprez P, Jakob C, Sommer T, Aebi M. Htm1 protein generates the N-glycan signal for glycoprotein degradation in the endoplasmic reticulum. ACTA ACUST UNITED AC 2009; 184:159-72. [PMID: 19124653 PMCID: PMC2615083 DOI: 10.1083/jcb.200809198] [Citation(s) in RCA: 189] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
To maintain protein homeostasis in secretory compartments, eukaryotic cells harbor a quality control system that monitors protein folding and protein complex assembly in the endoplasmic reticulum (ER). Proteins that do not fold properly or integrate into cognate complexes are degraded by ER-associated degradation (ERAD) involving retrotranslocation to the cytoplasm and proteasomal peptide hydrolysis. N-linked glycans are essential in glycoprotein ERAD; the covalent oligosaccharide structure is used as a signal to display the folding status of the host protein. In this study, we define the function of the Htm1 protein as an alpha1,2-specific exomannosidase that generates the Man(7)GlcNAc(2) oligosaccharide with a terminal alpha1,6-linked mannosyl residue on degradation substrates. This oligosaccharide signal is decoded by the ER-localized lectin Yos9p that in conjunction with Hrd3p triggers the ubiquitin-proteasome-dependent hydrolysis of these glycoproteins. The Htm1p exomannosidase activity requires processing of the N-glycan by glucosidase I, glucosidase II, and mannosidase I, resulting in a sequential order of specific N-glycan structures that reflect the folding status of the glycoprotein.
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98
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Slynko V, Schubert M, Numao S, Kowarik M, Aebi M, Allain FHT. NMR Structure Determination of a Segmentally Labeled Glycoprotein Using in Vitro Glycosylation. J Am Chem Soc 2009; 131:1274-81. [DOI: 10.1021/ja808682v] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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99
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Schulz BL, Aebi M. Analysis of glycosylation site occupancy reveals a role for Ost3p and Ost6p in site-specific N-glycosylation efficiency. Mol Cell Proteomics 2008; 8:357-64. [PMID: 18854577 DOI: 10.1074/mcp.m800219-mcp200] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Asparagine-linked glycosylation is the most common post-translational modification of proteins catalyzed in eukaryotes by the multiprotein complex oligosaccharyltransferase. Apart from the catalytic Stt3p, the roles of the subunits are ill defined. Here we describe functional investigations of the Ost3/6p components of the yeast enzyme. We developed novel analytical tools to quantify glycosylation site occupancy by enriching glycoproteins bound to the yeast polysaccharide cell wall, tagging glycosylated asparagines using endoglycosidase H glycan release, and detecting peptides and glycopeptides with LC-ESI-MS/MS. We found that the paralogues Ost3p and Ost6p were required for efficient glycosylation of distinct defined glycosylation sites. Our results describe a novel method for relative quantification of glycosylation occupancy in the genetically tractable yeast system and show that eukaryotic oligosaccharyltransferase isoforms have different activities toward protein substrates at the level of individual glycosylation sites.
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100
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Nasab FP, Schulz BL, Gamarro F, Parodi AJ, Aebi M. All in one: Leishmania major STT3 proteins substitute for the whole oligosaccharyltransferase complex in Saccharomyces cerevisiae. Mol Biol Cell 2008; 19:3758-68. [PMID: 18596231 DOI: 10.1091/mbc.e08-05-0467] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The transfer of lipid-linked oligosaccharide to asparagine residues of polypeptide chains is catalyzed by oligosaccharyltransferase (OTase). In most eukaryotes, OTase is a hetero-oligomeric complex composed of eight different proteins, in which the STT3 component is believed to be the catalytic subunit. In the parasitic protozoa Leishmania major, four STT3 paralogues, but no homologues to the other OTase components seem to be encoded in the genome. We expressed each of the four L. major STT3 proteins individually in Saccharomyces cerevisiae and found that three of them, LmSTT3A, LmSTT3B, and LmSTT3D, were able to complement a deletion of the yeast STT3 locus. Furthermore, LmSTT3D expression suppressed the lethal phenotype of single and double deletions in genes encoding other essential OTase subunits. LmSTT3 proteins did not incorporate into the yeast OTase complex but formed a homodimeric enzyme, capable of replacing the endogenous, multimeric enzyme of the yeast cell. Therefore, these protozoan OTases resemble the prokaryotic enzymes with respect to their architecture, but they used substrates typical for eukaryotic cells: N-X-S/T sequons in proteins and dolicholpyrophosphate-linked high mannose oligosaccharides.
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