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Journal ArticleDOI

Major glycan structure underlying expression of the Lewis X epitope in the developing brain is O-mannose-linked glycans on phosphacan/RPTPβ.

01 Apr 2015-Glycobiology (Oxford University Press)-Vol. 25, Iss: 4, pp 376-385

TL;DR: The results revealed the importance of O-mannosylated glycan chains in the presentation of functional glycan epitopes in the brain.

AbstractGlycosylation is a major protein modification. Although proteins are glycosylated/further modulated by several glycosyltransferases during trafficking from the endoplasmic reticulum to the Golgi apparatus, a certain glycan epitope has only been detected on a limited number of proteins. Of these glycan epitopes, Lewis X is highly expressed in the early stage of a developing brain and plays important roles in cell-cell interaction. The Lewis X epitope is comprised of a trisaccharide (Galβ1-4 (Fucα1-3) GlcNAc), and a key enzyme for the expression of this epitope is α1,3-fucosyltransferase 9. However, the scaffolding glycan structure responsible for the formation of the Lewis X epitope as well as its major carrier protein has not been fully characterized in the nervous system. Here we showed that the Lewis X epitope was mainly expressed on phosphacan/receptor protein tyrosine phosphatase β (RPTPβ) in the developing mouse brain. Expression of the Lewis X epitope was markedly reduced in β1,4-galactosyltransferase 2 (β4GalT2) gene-deficient mice, which indicated that β4GalT2 is a major galactosyltransferase required for the Lewis X epitope. We also showed that the Lewis X epitope almost disappeared due to the knockout of protein O-mannose β1,2-N-acetylglucosaminyltransferase 1, an N-acetylglucosaminyltransferase essential for the synthesis of O-mannosylated glycans, which indicated that the O-mannosylated glycan is responsible for presenting the Lewis X epitope. Since O-mannosylated glycans on phosphacan/RPTPβ could also present human natural killer-1, another glycan epitope specifically expressed in the nervous system, our results revealed the importance of O-mannosylated glycan chains in the presentation of functional glycan epitopes in the brain.

Topics: Linear epitope (67%), Epitope (62%), Glycan (62%), Glycosylation (54%)

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Citations
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Journal ArticleDOI
TL;DR: Following this educational survey, examples where known biological function is related to the glycan structures carried by proteins are given and mucins and their glycosylation patterns are considered as instructive proof-of-principle case.
Abstract: Proteins undergo co- and posttranslational modifications, and their glycosylation is the most frequent and structurally variegated type. Histochemically, the detection of glycan presence has first been performed by stains. The availability of carbohydrate-specific tools (lectins, monoclonal antibodies) has revolutionized glycophenotyping, allowing monitoring of distinct structures. The different types of protein glycosylation in Eukaryotes are described. Following this educational survey, examples where known biological function is related to the glycan structures carried by proteins are given. In particular, mucins and their glycosylation patterns are considered as instructive proof-of-principle case. The tissue and cellular location of glycoprotein biosynthesis and metabolism is reviewed, with attention to new findings in goblet cells. Finally, protein glycosylation in disease is documented, with selected examples, where aberrant glycan expression impacts on normal function to let disease pathology become manifest. The histological applications adopted in these studies are emphasized throughout the text.

91 citations


Cites background from "Major glycan structure underlying e..."

  • ...…Yanagisawa) coding Galβ1,4(Fucα1,3)GlcNAcβ1- (Yu and Yanagisawa 2006), while O-mannosylation is also a significant feature of α-dystroglycan in the nervous system, where it mediates cell-extracellular matrix contact (Hennet 2009; Panin and Wells 2014; Praissman and Wells 2014; Yaji et al. 2015)....

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  • ...Neural stem cells express CD15 (Yu and Yanagisawa) coding Galβ1,4(Fucα1,3)GlcNAcβ1- (Yu and Yanagisawa 2006), while O-mannosylation is also a significant feature of α-dystroglycan in the nervous system, where it mediates cell-extracellular matrix contact (Hennet 2009; Panin and Wells 2014; Praissman and Wells 2014; Yaji et al. 2015)....

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Journal ArticleDOI
TL;DR: This review will focus on recent discoveries delineating the various enzymes, structures and functions associated with O-mannose-initiated glycoproteins, and discusses the evolution of this pathway.
Abstract: The post-translational glycosylation of select proteins by O-linked mannose (O-mannose or O-man) is a conserved modification from yeast to humans and has been shown to be necessary for proper development and growth. The most well studied O-mannosylated mammalian protein is α-dystroglycan (α-DG). Hypoglycosylation of α-DG results in varying severities of congenital muscular dystrophies, cancer progression and metastasis, and inhibited entry and infection of certain arenaviruses. Defects in the gene products responsible for post-translational modification of α-DG, primarily glycosyltransferases, are the basis for these diseases. The multitude of clinical phenotypes resulting from defective O-mannosylation highlights the biomedical significance of this unique modification. Elucidation of the various O-mannose biosynthetic pathways is imperative to understanding a broad range of human diseases and for the development of novel therapeutics. In this review, we will focus on recent discoveries delineating the various enzymes, structures and functions associated with O-mannose-initiated glycoproteins. Additionally, we discuss current gaps in our knowledge of mammalian O-mannosylation, discuss the evolution of this pathway, and illustrate the utility and limitations of model systems to study functions of O-mannosylation.

50 citations


Journal ArticleDOI
TL;DR: GDP-l-fucose synthase is an autoantigen recognized by cerebrospinal fluid–infiltrating CD4+ T cells from HLA-DRB3*–positive patients with multiple sclerosis, and the possible role of this antigen as an inducer or driver of pathogenic autoimmune responses in multiple sclerosis is suggested.
Abstract: Multiple sclerosis is an immune-mediated autoimmune disease of the central nervous system that develops in genetically susceptible individuals and likely requires environmental triggers. The autoantigens and molecular mimics triggering the autoimmune response in multiple sclerosis remain incompletely understood. By using a brain-infiltrating CD4 + T cell clone that is clonally expanded in multiple sclerosis brain lesions and a systematic approach for the identification of its target antigens, positional scanning peptide libraries in combination with biometrical analysis, we have identified guanosine diphosphate (GDP)–l-fucose synthase as an autoantigen that is recognized by cerebrospinal fluid–infiltrating CD4 + T cells from HLA-DRB3*–positive patients. Significant associations were found between reactivity to GDP-l-fucose synthase peptides and DRB3*02:02 expression, along with reactivity against an immunodominant myelin basic protein peptide. These results, coupled with the cross-recognition of homologous peptides from gut microbiota, suggest a possible role of this antigen as an inducer or driver of pathogenic autoimmune responses in multiple sclerosis.

46 citations


Journal ArticleDOI
01 Aug 2016-Glia
TL;DR: It is shown that LeX‐glycosylated LRP1 is also expressed in the stem cell compartment of the developing spinal cord and has broader functions in the developing CNS, suggesting that LRP 1 facilitates NSPCs differentiation via interaction with apolipoprotein E (ApoE).
Abstract: The LDL family of receptors and its member low-density lipoprotein receptor-related protein 1 (LRP1) have classically been associated with a modulation of lipoprotein metabolism. Current studies, however, indicate diverse functions for this receptor in various aspects of cellular activities, including cell proliferation, migration, differentiation, and survival. LRP1 is essential for normal neuronal function in the adult CNS, whereas the role of LRP1 in development remained unclear. Previously, we have observed an upregulation of LewisX (LeX) glycosylated LRP1 in the stem cells of the developing cortex and demonstrated its importance for oligodendrocyte differentiation. In the current study, we show that LeX-glycosylated LRP1 is also expressed in the stem cell compartment of the developing spinal cord and has broader functions in the developing CNS. We have investigated the basic properties of LRP1 conditional knockout on the neural stem/progenitor cells (NSPCs) from the cortex and the spinal cord, created by means of Cre-loxp-mediated recombination in vitro. The functional status of LRP1-deficient cells has been studied using proliferation, differentiation, and apoptosis assays. LRP1 deficient NSPCs from both CNS regions demonstrated altered differentiation profiles. Their differentiation capacity toward oligodendrocyte progenitor cells (OPCs), mature oligodendrocytes and neurons was reduced. In contrast, astrocyte differentiation was promoted. Moreover, LRP1 deletion had a negative effect on NSPCs proliferation and survival. Our observations suggest that LRP1 facilitates NSPCs differentiation via interaction with apolipoprotein E (ApoE). Upon ApoE4 stimulation wild type NSPCs generated more oligodendrocytes, but LRP1 knockout cells showed no response. The effect of ApoE seems to be independent of cholesterol uptake, but is rather mediated by downstream MAPK and Akt activation. GLIA 2016 GLIA 2016;64:1363-1380.

36 citations


Cites background from "Major glycan structure underlying e..."

  • ...We confirmed already known LeX presenting proteins such as phosphacan, tenascin-C, and L1-CAM (Garwood et al., 1999; Hennen et al., 2013; Streit et al., 1990; Yaji et al., 2015)....

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Journal ArticleDOI
TL;DR: O-mannosyl glycan has a novel, unique structure that is important for the maintenance of brain and muscle functions that has opened up a new field in glycoscience.
Abstract: Background O -mannosyl glycans have been found in a limited number of glycoproteins of the brain, nerves, and skeletal muscles, particularly in α-dystroglycan (α-DG). Defects in O -mannosyl glycan on α-DG are the primary cause of a group of congenital muscular dystrophies, which are collectively termed α-dystroglycanopathy. Recent studies have revealed various O -mannosyl glycan structures, which can be classified as core M1, core M2, and core M3 glycans. Although many dystroglycanopathy genes are involved in core M3 processing, the structure and biosynthesis of core M3 glycan remains only partially understood. Scope of review This review presents recent findings about the structure, biosynthesis, and pathology of O -mannosyl glycans. Major conclusions Recent studies have revealed that the entire structure of core M3 glycan, including ribitol-5-phosphate, is a novel structure in mammals; its unique biosynthetic pathway has been elucidated by the identification of new causative genes for α-dystroglycanopathies and their functions. General significance O -mannosyl glycan has a novel, unique structure that is important for the maintenance of brain and muscle functions. These findings have opened up a new field in glycoscience. These studies will further contribute to the understanding of the pathomechanism of α-dystroglycanopathy and the development of glycotherapeutics. This article is part of a Special Issue entitled Neuro-glycoscience, edited by Kenji Kadomatsu and Hiroshi Kitagawa.

36 citations


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Journal ArticleDOI
TL;DR: It is concluded that the majority of sequon containing proteins will be found to be glycosylated and that more than half of all proteins are glycoproteins.
Abstract: The SWISS-PROT protein sequence data bank contains at present nearly 75,000 entries, almost two thirds of which include the potential N-glycosylation consensus sequence, or sequon, NXS/T (where X can be any amino acid but proline) and thus may be glycoproteins. The number of proteins filed as glycoproteins is however considerably smaller, 7942, of which 749 have been characterized with respect to the total number of their carbohydrate units and sites of attachment of the latter to the protein, as well as the nature of the carbohydrate-peptide linking group. Of these well characterized glycoproteins, about 90% carry either N-linked carbohydrate units alone or both N- and O-linked ones, attached at 1297 N-glycosylation sites (1.9 per glycoprotein molecule) and the rest are O-glycosylated only. Since the total number of sequons in the well characterized glycoproteins is 1968, their rate of occupancy is 2/3. Assuming that the same number of N-linked units and rate of sequon occupancy occur in all sequon containing proteins and that the proportion of solely O-glycosylated proteins (ca. 10%) will also be the same as among the well characterized ones, we conclude that the majority of sequon containing proteins will be found to be glycosylated and that more than half of all proteins are glycoproteins.

1,646 citations


"Major glycan structure underlying e..." refers background in this paper

  • ...Glycosylation is one of the most frequent post-translational modifications of proteins (Apweiler et al. 1999)....

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Journal ArticleDOI
TL;DR: It is suggested that interference in O-mannosyl glycosylation is a new pathomechanism for muscular dystrophy as well as neuronal migration disorder.
Abstract: Muscle-eye-brain disease (MEB) is an autosomal recessive disorder characterized by congenital muscular dystrophy, ocular abnormalities, and lissencephaly. Mammalian O- mannosyl glycosylation is a rare type of protein modification that is observed in a limited number of glycoproteins of brain, nerve, and skeletal muscle. Here we isolated a human cDNA for protein O -mannose β-1,2- N -acetylglucosaminyltransferase (POMGnT1), which participates in O -mannosyl glycan synthesis. We also identified six independent mutations of the POMGnT1 gene in six patients with MEB. Expression of most frequent mutation revealed a great loss of the enzymatic activity. These findings suggest that interference in O -mannosyl glycosylation is a new pathomechanism for muscular dystrophy as well as neuronal migration disorder.

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"Major glycan structure underlying e..." refers background or methods in this paper

  • ...…known to be biosynthesized by the first enzyme POMT (Beltran-Valero de Bernabe et al. 2002), and N-acetylglucosamine at O ndokuz M ayis U niversity on N ovem ber 12, 2014 http://glycob.oxfordjournals.org/ D ow nloaded from (GlcNAc) could be transferred to O-mannose by POMGnT1 (Yoshida et al. 2001)....

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  • ...1997) and was synthesized by protein O-mannosyl transferase 1 (POMT1), POMT2, and protein O-mannose β1,2-N-acetylglucosaminyltransferase 1 (POMGnT1) (Yoshida et al. 2001; Manya et al. 2004)....

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  • ...Mutations in the genes encoding POMT1/2 and POMGnT1 have been shown to cause muscular dystrophies with abnormal -DG glycosylation, designated as Walker-Warburg syndrome and muscle-eye-brain disease, respectively (Yoshida et al. 2001; Beltran-Valero de Bernabe et al. 2002; van Reeuwijk et al. 2005)....

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  • ...…(Siaα2-3Galβ1-4GlcNAcβ1-2Man) was discovered in bovine peripheral nerve α-dystroglycan (α-DG) (Chiba et al. 1997) and was synthesized by protein O-mannosyl transferase 1 (POMT1), POMT2, and protein O-mannose β1,2-N-acetylglucosaminyltransferase 1 (POMGnT1) (Yoshida et al. 2001; Manya et al. 2004)....

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  • ...(GlcNAc) could be transferred to O-mannose by POMGnT1 (Yoshida et al. 2001)....

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Journal ArticleDOI
TL;DR: Immunohistochemical analysis of muscle from patients with POMT1 mutations corroborated the O-mannosylation defect, as judged by the absence of glycosylation of alpha-dystroglycan.
Abstract: Walker-Warburg syndrome (WWS) is an autosomal recessive developmental disorder characterized by congenital muscular dystrophy and complex brain and eye abnormalities. A similar combination of symptoms is presented by two other human diseases, muscle-eye-brain disease (MEB) and Fukuyama congenital muscular dystrophy (FCMD). Although the genes underlying FCMD (Fukutin) and MEB (POMGnT1) have been cloned, loci for WWS have remained elusive. The protein products of POMGnT1 and Fukutin have both been implicated in protein glycosylation. To unravel the genetic basis of WWS, we first performed a genomewide linkage analysis in 10 consanguineous families with WWS. The results indicated the existence of at least three WWS loci. Subsequently, we adopted a candidate-gene approach in combination with homozygosity mapping in 15 consanguineous families with WWS. Candidate genes were selected on the basis of the role of the FCMD and MEB genes. Since POMGnT1 encodes an O-mannoside N-acetylglucosaminyltransferase, we analyzed the possible implication of O-mannosyl glycan synthesis in WWS. Analysis of the locus for O-mannosyltransferase 1 (POMT1) revealed homozygosity in 5 of 15 families. Sequencing of the POMT1 gene revealed mutations in 6 of the 30 unrelated patients with WWS. Of the five mutations identified, two are nonsense mutations, two are frameshift mutations, and one is a missense mutation. Immunohistochemical analysis of muscle from patients with POMT1 mutations corroborated the O-mannosylation defect, as judged by the absence of glycosylation of α-dystroglycan. The implication of O-mannosylation in MEB and WWS suggests new lines of study in understanding the molecular basis of neuronal migration.

632 citations


"Major glycan structure underlying e..." refers background in this paper

  • ...Mutations in the genes encoding POMT1/2 and POMGnT1 have been shown to cause muscular dystrophies with abnormal -DG glycosylation, designated as Walker-Warburg syndrome and muscle-eye-brain disease, respectively (Yoshida et al. 2001; Beltran-Valero de Bernabe et al. 2002; van Reeuwijk et al. 2005)....

    [...]

  • ...O-mannosyl glycans are known to be biosynthesized by the first enzyme POMT (Beltran-Valero de Bernabe et al. 2002), and N-acetylglucosamine at O ndokuz M ayis U niversity on N ovem ber 12, 2014 http://glycob.oxfordjournals.org/ D ow nloaded from (GlcNAc) could be transferred to O-mannose by POMGnT1…...

    [...]


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