N-linked glycosylation is the most important form of post-translational modification for proteins synthesized and folded in the Endoplasmic Reticulum (Stanley P et al, 2009). An early study in 1999 revealed that about 50% of the proteins in the Swiss-Prot database at the time were N-glycosylated (Apweiler R et al, 1999). It is now established that the majority of the proteins in the secretory pathway require glycosylation in order to achieve proper folding. The addition of an N-glycan to a protein can have several roles (Shental-Bechor D and Levy Y, 2009). First, glycans enhance the solubility and stability of the proteins in the ER, the golgi and on the outside of the cell membrane, where the composition of the medium is strongly hydrophilic and where proteins, that are mostly hydrophobic, have difficulty folding properly. Second, N-glycans are used as signal molecules during the folding and transport process of the protein: they have the role of labels to determine when a protein must interact with a chaperon, be transported to the golgi, or targeted for degradation in case of major folding defects. Third, and most importantly, N-glycans on completely folded proteins are involved in a wide range of processes: they help determine the specificity of membrane receptors in innate immunity or in cell-to-cell interactions, they can change the properties of hormones and secreted proteins, or of the proteins in the vesicular system inside the cell. All N-linked glycans are derived from a common 14-sugar oligosaccharide synthesized in the ER, which is attached co-translationally to a protein while this is being translated inside the reticulum. The process of the synthesis of this glycan, known as Synthesis of the N-glycan precursor or LLO, constitutes one of the most conserved pathways in eukaryotes, and has been also observed in some eubacteria. The attachment usually happens on an asparagine residue within the consensus sequence asparagine-X-threonine by an complex called oligosaccharyl transferase (OST). After being attached to an unfolded protein, the glycan is used as a label molecule in the folding process (also known as Calnexin/Calreticulin cycle) (Lederkremer GZ, 2009). The majority of the glycoproteins in the ER require at least one glycosylated residue in order to achieve proper folding, even if it has been shown that a smaller portion of the proteins in the ER can be folded without this modification. Once the glycoprotein has achieved proper folding, it is transported via the Cis-golgi through all the Golgi compartments, where the glycan is further modified according to the properties of the glycoprotein. This process involves relatively few enzymes but due to its combinatorial nature, can lead to several millions of different possible modifications. The exact topography of this network of reactions has not been established yet, representing one of the major challenges after the sequencing of the human genome (Hossler P et al, 2006). Since N-glycosylation is involved in an great number of different processes, from cell-cell interaction to folding control, mutations in one of the genes involved in glycan assembly and/or modification can lead to severe development problems (often affecting the central nervous system). All the diseases in genes involved in glycosylation are collectively known as Congenital Disorders of Glycosylation (CDG) (Sparks SE et al, 2003), and classified as CDG type I for the genes in the LLO synthesis pathway, and CDG type II for the others.
Schenk B, Fernandez F, Waechter CJ.; ''The ins(ide) and out(side) of dolichyl phosphate biosynthesis and recycling in the endoplasmic reticulum.''; PubMedEurope PMCScholia
Wang Y, Schachter H, Marth JD.; ''Mice with a homozygous deletion of the Mgat2 gene encoding UDP-N-acetylglucosamine:alpha-6-D-mannoside beta1,2-N-acetylglucosaminyltransferase II: a model for congenital disorder of glycosylation type IIa.''; PubMedEurope PMCScholia
Pearse BR, Gabriel L, Wang N, Hebert DN.; ''A cell-based reglucosylation assay demonstrates the role of GT1 in the quality control of a maturing glycoprotein.''; PubMedEurope PMCScholia
Bernasconi R, Pertel T, Luban J, Molinari M.; ''A dual task for the Xbp1-responsive OS-9 variants in the mammalian endoplasmic reticulum: inhibiting secretion of misfolded protein conformers and enhancing their disposal.''; PubMedEurope PMCScholia
Shental-Bechor D, Levy Y.; ''Folding of glycoproteins: toward understanding the biophysics of the glycosylation code.''; PubMedEurope PMCScholia
Shridas P, Rush JS, Waechter CJ.; ''Identification and characterization of a cDNA encoding a long-chain cis-isoprenyltranferase involved in dolichyl monophosphate biosynthesis in the ER of brain cells.''; PubMedEurope PMCScholia
Yik JH, Saxena A, Weigel JA, Weigel PH.; ''Nonpalmitoylated human asialoglycoprotein receptors recycle constitutively but are defective in coated pit-mediated endocytosis, dissociation, and delivery of ligand to lysosomes.''; PubMedEurope PMCScholia
Song Y, Aglipay JA, Bernstein JD, Goswami S, Stanley P.; ''The bisecting GlcNAc on N-glycans inhibits growth factor signaling and retards mammary tumor progression.''; PubMedEurope PMCScholia
Hinderlich S, Berger M, Blume A, Chen H, Ghaderi D, Bauer C.; ''Identification of human L-fucose kinase amino acid sequence.''; PubMedEurope PMCScholia
Kahrizi K, Hu CH, Garshasbi M, Abedini SS, Ghadami S, Kariminejad R, Ullmann R, Chen W, Ropers HH, Kuss AW, Najmabadi H, Tzschach A.; ''Next generation sequencing in a family with autosomal recessive Kahrizi syndrome (OMIM 612713) reveals a homozygous frameshift mutation in SRD5A3.''; PubMedEurope PMCScholia
Xia G, Evers MR, Kang HG, Schachner M, Baenziger JU.; ''Molecular cloning and expression of the pituitary glycoprotein hormone N-acetylgalactosamine-4-O-sulfotransferase.''; PubMedEurope PMCScholia
Haeuptle MA, Pujol FM, Neupert C, Winchester B, Kastaniotis AJ, Aebi M, Hennet T.; ''Human RFT1 deficiency leads to a disorder of N-linked glycosylation.''; PubMedEurope PMCScholia
Oki T, Yamazaki K, Kuromitsu J, Okada M, Tanaka I.; ''cDNA cloning and mapping of a novel subtype of glutamine:fructose-6-phosphate amidotransferase (GFAT2) in human and mouse.''; PubMedEurope PMCScholia
Moore SE, Spiro RG.; ''Demonstration that Golgi endo-alpha-D-mannosidase provides a glucosidase-independent pathway for the formation of complex N-linked oligosaccharides of glycoproteins.''; PubMedEurope PMCScholia
Ong E, Yeh JC, Ding Y, Hindsgaul O, Pedersen LC, Negishi M, Fukuda M.; ''Structure and function of HNK-1 sulfotransferase. Identification of donor and acceptor binding sites by site-directed mutagenesis.''; PubMedEurope PMCScholia
Breuer W, Klein RA, Hardt B, Bartoschek A, Bause E.; ''Oligosaccharyltransferase is highly specific for the hydroxy amino acid in Asn-Xaa-Thr/Ser.''; PubMedEurope PMCScholia
Weinstein M, Schollen E, Matthijs G, Neupert C, Hennet T, Grubenmann CE, Frank CG, Aebi M, Clarke JT, Griffiths A, Seargeant L, Poplawski N.; ''CDG-IL: an infant with a novel mutation in the ALG9 gene and additional phenotypic features.''; PubMedEurope PMCScholia
Katiyar S, Joshi S, Lennarz WJ.; ''The retrotranslocation protein Derlin-1 binds peptide:N-glycanase to the endoplasmic reticulum.''; PubMedEurope PMCScholia
Baysal BE, Willett-Brozick JE, Bacanu SA, Detera-Wadleigh S, Nimgaonkar VL.; ''Common variations in ALG9 are not associated with bipolar I disorder: a family-based study.''; PubMedEurope PMCScholia
Verachtert H, Rodriguez P, Bass ST, Hansen RG.; ''Purification and properties of guanosine diphosphate hexose pyrophosphorylase from mammalian tissues.''; PubMedEurope PMCScholia
Hauri H, Appenzeller C, Kuhn F, Nufer O.; ''Lectins and traffic in the secretory pathway.''; PubMedEurope PMCScholia
Hamilton SR, Li H, Wischnewski H, Prasad A, Kerley-Hamilton JS, Mitchell T, Walling AJ, Davidson RC, Wildt S, Gerngross TU.; ''Intact {alpha}-1,2-endomannosidase is a typical type II membrane protein.''; PubMedEurope PMCScholia
Guo S, Sato T, Shirane K, Furukawa K.; ''Galactosylation of N-linked oligosaccharides by human beta-1,4-galactosyltransferases I, II, III, IV, V, and VI expressed in Sf-9 cells.''; PubMedEurope PMCScholia
Ellies LG, Ditto D, Levy GG, Wahrenbrock M, Ginsburg D, Varki A, Le DT, Marth JD.; ''Sialyltransferase ST3Gal-IV operates as a dominant modifier of hemostasis by concealing asialoglycoprotein receptor ligands.''; PubMedEurope PMCScholia
Takahashi S, Takahashi K, Kaneko T, Ogasawara H, Shindo S, Kobayashi M.; ''Human renin-binding protein is the enzyme N-acetyl-D-glucosamine 2-epimerase.''; PubMedEurope PMCScholia
McNeill H, Knebel A, Arthur JS, Cuenda A, Cohen P.; ''A novel UBA and UBX domain protein that binds polyubiquitin and VCP and is a substrate for SAPKs.''; PubMedEurope PMCScholia
Toth MJ, Huwyler L.; ''Molecular cloning and expression of the cDNAs encoding human and yeast mevalonate pyrophosphate decarboxylase.''; PubMedEurope PMCScholia
Harrison KD, Park EJ, Gao N, Kuo A, Rush JS, Waechter CJ, Lehrman MA, Sessa WC.; ''Nogo-B receptor is necessary for cellular dolichol biosynthesis and protein N-glycosylation.''; PubMedEurope PMCScholia
Nakayama K, Moriwaki K, Imai T, Shinzaki S, Kamada Y, Murata K, Miyoshi E.; ''Mutation of GDP-mannose-4,6-dehydratase in colorectal cancer metastasis.''; PubMedEurope PMCScholia
Ong E, Yeh JC, Ding Y, Hindsgaul O, Fukuda M.; ''Expression cloning of a human sulfotransferase that directs the synthesis of the HNK-1 glycan on the neural cell adhesion molecule and glycolipids.''; PubMedEurope PMCScholia
Varki NM, Strobert E, Dick EJ, Benirschke K, Varki A.; ''Biomedical differences between human and nonhuman hominids: potential roles for uniquely human aspects of sialic acid biology.''; PubMedEurope PMCScholia
Belaya K, Finlayson S, Slater CR, Cossins J, Liu WW, Maxwell S, McGowan SJ, Maslau S, Twigg SR, Walls TJ, Pascual Pascual SI, Palace J, Beeson D.; ''Mutations in DPAGT1 cause a limb-girdle congenital myasthenic syndrome with tubular aggregates.''; PubMedEurope PMCScholia
Angata K, Nakayama J, Fredette B, Chong K, Ranscht B, Fukuda M.; ''Human STX polysialyltransferase forms the embryonic form of the neural cell adhesion molecule. Tissue-specific expression, neurite outgrowth, and chromosomal localization in comparison with another polysialyltransferase, PST.''; PubMedEurope PMCScholia
Sullivan FX, Kumar R, Kriz R, Stahl M, Xu GY, Rouse J, Chang XJ, Boodhoo A, Potvin B, Cumming DA.; ''Molecular cloning of human GDP-mannose 4,6-dehydratase and reconstitution of GDP-fucose biosynthesis in vitro.''; PubMedEurope PMCScholia
Proudfoot AE, Turcatti G, Wells TN, Payton MA, Smith DJ.; ''Purification, cDNA cloning and heterologous expression of human phosphomannose isomerase.''; PubMedEurope PMCScholia
Oguri S, Yoshida A, Minowa MT, Takeuchi M.; ''Kinetic properties and substrate specificities of two recombinant human N-acetylglucosaminyltransferase-IV isozymes.''; PubMedEurope PMCScholia
Lopez LC, Youakim A, Evans SC, Shur BD.; ''Evidence for a molecular distinction between Golgi and cell surface forms of beta 1,4-galactosyltransferase.''; PubMedEurope PMCScholia
Crispin M, Aricescu AR, Chang VT, Jones EY, Stuart DI, Dwek RA, Davis SJ, Harvey DJ.; ''Disruption of alpha-mannosidase processing induces non-canonical hybrid-type glycosylation.''; PubMedEurope PMCScholia
Bischoff J, Libresco S, Shia MA, Lodish HF.; ''The H1 and H2 polypeptides associate to form the asialoglycoprotein receptor in human hepatoma cells.''; PubMedEurope PMCScholia
Weihofen WA, Berger M, Chen H, Saenger W, Hinderlich S.; ''Structures of human N-Acetylglucosamine kinase in two complexes with N-Acetylglucosamine and with ADP/glucose: insights into substrate specificity and regulation.''; PubMedEurope PMCScholia
Stanley P.; ''Biological consequences of overexpressing or eliminating N-acetylglucosaminyltransferase-TIII in the mouse.''; PubMedEurope PMCScholia
Zhang B, Cunningham MA, Nichols WC, Bernat JA, Seligsohn U, Pipe SW, McVey JH, Schulte-Overberg U, de Bosch NB, Ruiz-Saez A, White GC, Tuddenham EG, Kaufman RJ, Ginsburg D.; ''Bleeding due to disruption of a cargo-specific ER-to-Golgi transport complex.''; PubMedEurope PMCScholia
Wu X, Rush JS, Karaoglu D, Krasnewich D, Lubinsky MS, Waechter CJ, Gilmore R, Freeze HH.; ''Deficiency of UDP-GlcNAc:Dolichol Phosphate N-Acetylglucosamine-1 Phosphate Transferase (DPAGT1) causes a novel congenital disorder of Glycosylation Type Ij.''; PubMedEurope PMCScholia
van Lith M, Karala AR, Bown D, Gatehouse JA, Ruddock LW, Saunders PT, Benham AM.; ''A developmentally regulated chaperone complex for the endoplasmic reticulum of male haploid germ cells.''; PubMedEurope PMCScholia
Fernandez F, Shridas P, Jiang S, Aebi M, Waechter CJ.; ''Expression and characterization of a human cDNA that complements the temperature-sensitive defect in dolichol kinase activity in the yeast sec59-1 mutant: the enzymatic phosphorylation of dolichol and diacylglycerol are catalyzed by separate CTP-mediated kinase activities in Saccharomyces cerevisiae.''; PubMedEurope PMCScholia
Krzewinski-Recchi MA, Julien S, Juliant S, Teintenier-Lelièvre M, Samyn-Petit B, Montiel MD, Mir AM, Cerutti M, Harduin-Lepers A, Delannoy P.; ''Identification and functional expression of a second human beta-galactoside alpha2,6-sialyltransferase, ST6Gal II.''; PubMedEurope PMCScholia
Sanyal S, Frank CG, Menon AK.; ''Distinct flippases translocate glycerophospholipids and oligosaccharide diphosphate dolichols across the endoplasmic reticulum.''; PubMedEurope PMCScholia
Hauri HP, Nufer O, Breuza L, Tekaya HB, Liang L.; ''Lectins and protein traffic early in the secretory pathway.''; PubMedEurope PMCScholia
Katiyar S, Li G, Lennarz WJ.; ''A complex between peptide:N-glycanase and two proteasome-linked proteins suggests a mechanism for the degradation of misfolded glycoproteins.''; PubMedEurope PMCScholia
Freeman DJ, Rupar CA, Carroll KK.; ''Analysis of dolichol in human tissues by high pressure liquid chromatography.''; PubMedEurope PMCScholia
Ye Y, Shibata Y, Yun C, Ron D, Rapoport TA.; ''A membrane protein complex mediates retro-translocation from the ER lumen into the cytosol.''; PubMedEurope PMCScholia
Molinari M.; ''N-glycan structure dictates extension of protein folding or onset of disposal.''; PubMedEurope PMCScholia
Hossler P, Goh LT, Lee MM, Hu WS.; ''GlycoVis: visualizing glycan distribution in the protein N-glycosylation pathway in mammalian cells.''; PubMedEurope PMCScholia
Schollen E, Frank CG, Keldermans L, Reyntjens R, Grubenmann CE, Clayton PT, Winchester BG, Smeitink J, Wevers RA, Aebi M, Hennet T, Matthijs G.; ''Clinical and molecular features of three patients with congenital disorders of glycosylation type Ih (CDG-Ih) (ALG8 deficiency).''; PubMedEurope PMCScholia
Cantz M, Gehler J.; ''The mucopolysaccharidoses: inborn errors of glycosaminoglycan catabolism.''; PubMedEurope PMCScholia
Baysal BE, Willett-Brozick JE, Badner JA, Corona W, Ferrell RE, Nimgaonkar VL, Detera-Wadleigh SD.; ''A mannosyltransferase gene at 11q23 is disrupted by a translocation breakpoint that co-segregates with bipolar affective disorder in a small family.''; PubMedEurope PMCScholia
Dall'Olio F.; ''The sialyl-alpha2,6-lactosaminyl-structure: biosynthesis and functional role.''; PubMedEurope PMCScholia
Hirao K, Natsuka Y, Tamura T, Wada I, Morito D, Natsuka S, Romero P, Sleno B, Tremblay LO, Herscovics A, Nagata K, Hosokawa N.; ''EDEM3, a soluble EDEM homolog, enhances glycoprotein endoplasmic reticulum-associated degradation and mannose trimming.''; PubMedEurope PMCScholia
Soh CP, Morgan WT, Watkins WM, Donald AS.; ''The relationship between the N-acetylgalactosamine content and the blood group Sda activity of Tamm and Horsfall urinary glycoprotein.''; PubMedEurope PMCScholia
Eckert V, Blank M, Mazhari-Tabrizi R, Mumberg D, Funk M, Schwarz RT.; ''Cloning and functional expression of the human GlcNAc-1-P transferase, the enzyme for the committed step of the dolichol cycle, by heterologous complementation in Saccharomyces cerevisiae.''; PubMedEurope PMCScholia
Völker C, De Praeter CM, Hardt B, Breuer W, Kalz-Füller B, Van Coster RN, Bause E.; ''Processing of N-linked carbohydrate chains in a patient with glucosidase I deficiency (CDG type IIb).''; PubMedEurope PMCScholia
Sun L, Eklund EA, Van Hove JL, Freeze HH, Thomas JA.; ''Clinical and molecular characterization of the first adult congenital disorder of glycosylation (CDG) type Ic patient.''; PubMedEurope PMCScholia
Yamaguchi Y, Fujii J, Inoue S, Uozumi N, Yanagidani S, Ikeda Y, Egashira M, Miyoshi O, Niikawa N, Taniguchi N.; ''Mapping of the alpha-1,6-fucosyltransferase gene, FUT8, to human chromosome 14q24.3.''; PubMedEurope PMCScholia
Schauer R.; ''Achievements and challenges of sialic acid research.''; PubMedEurope PMCScholia
Ninagawa S, Okada T, Sumitomo Y, Kamiya Y, Kato K, Horimoto S, Ishikawa T, Takeda S, Sakuma T, Yamamoto T, Mori K.; ''EDEM2 initiates mammalian glycoprotein ERAD by catalyzing the first mannose trimming step.''; PubMedEurope PMCScholia
Wang J, Liu X, Liang YH, Li LF, Su XD.; ''Acceptor substrate binding revealed by crystal structure of human glucosamine-6-phosphate N-acetyltransferase 1.''; PubMedEurope PMCScholia
Li Y, Chen X.; ''Sialic acid metabolism and sialyltransferases: natural functions and applications.''; PubMedEurope PMCScholia
Avezov E, Frenkel Z, Ehrlich M, Herscovics A, Lederkremer GZ.; ''Endoplasmic reticulum (ER) mannosidase I is compartmentalized and required for N-glycan trimming to Man5-6GlcNAc2 in glycoprotein ER-associated degradation.''; PubMedEurope PMCScholia
Park C, Jin UH, Lee YC, Cho TJ, Kim CH.; ''Characterization of UDP-N-acetylglucosamine:alpha-6-d-mannoside beta-1,6-N-acetylglucosaminyltransferase V from a human hepatoma cell line Hep3B.''; PubMedEurope PMCScholia
Tan J, D'Agostaro AF, Bendiak B, Reck F, Sarkar M, Squire JA, Leong P, Schachter H.; ''The human UDP-N-acetylglucosamine: alpha-6-D-mannoside-beta-1,2- N-acetylglucosaminyltransferase II gene (MGAT2). Cloning of genomic DNA, localization to chromosome 14q21, expression in insect cells and purification of the recombinant protein.''; PubMedEurope PMCScholia
De Praeter CM, Gerwig GJ, Bause E, Nuytinck LK, Vliegenthart JF, Breuer W, Kamerling JP, Espeel MF, Martin JJ, De Paepe AM, Chan NW, Dacremont GA, Van Coster RN.; ''A novel disorder caused by defective biosynthesis of N-linked oligosaccharides due to glucosidase I deficiency.''; PubMedEurope PMCScholia
Lübke T, Marquardt T, Etzioni A, Hartmann E, von Figura K, Körner C.; ''Complementation cloning identifies CDG-IIc, a new type of congenital disorders of glycosylation, as a GDP-fucose transporter deficiency.''; PubMedEurope PMCScholia
Pelletier MF, Marcil A, Sevigny G, Jakob CA, Tessier DC, Chevet E, Menard R, Bergeron JJ, Thomas DY.; ''The heterodimeric structure of glucosidase II is required for its activity, solubility, and localization in vivo.''; PubMedEurope PMCScholia
Lo NW, Shaper JH, Pevsner J, Shaper NL.; ''The expanding beta 4-galactosyltransferase gene family: messages from the databanks.''; PubMedEurope PMCScholia
Nyfeler B, Nufer O, Matsui T, Mori K, Hauri HP.; ''The cargo receptor ERGIC-53 is a target of the unfolded protein response.''; PubMedEurope PMCScholia
Tan J, Dunn J, Jaeken J, Schachter H.; ''Mutations in the MGAT2 gene controlling complex N-glycan synthesis cause carbohydrate-deficient glycoprotein syndrome type II, an autosomal recessive disease with defective brain development.''; PubMedEurope PMCScholia
Dall'Olio F, Malagolini N, Chiricolo M, Trinchera M, Harduin-Lepers A.; ''The expanding roles of the Sd(a)/Cad carbohydrate antigen and its cognate glycosyltransferase B4GALNT2.''; PubMedEurope PMCScholia
Ning B, Elbein AD.; ''Cloning, expression and characterization of the pig liver GDP-mannose pyrophosphorylase. Evidence that GDP-mannose and GDP-Glc pyrophosphorylases are different proteins.''; PubMedEurope PMCScholia
Yagi T, Baroja-Fernández E, Yamamoto R, Muñoz FJ, Akazawa T, Hong KS, Pozueta-Romero J.; ''Cloning, expression and characterization of a mammalian Nudix hydrolase-like enzyme that cleaves the pyrophosphate bond of UDP-glucose.''; PubMedEurope PMCScholia
Helenius J, Ng DT, Marolda CL, Walter P, Valvano MA, Aebi M.; ''Translocation of lipid-linked oligosaccharides across the ER membrane requires Rft1 protein.''; PubMedEurope PMCScholia
Arnold SM, Fessler LI, Fessler JH, Kaufman RJ.; ''Two homologues encoding human UDP-glucose:glycoprotein glucosyltransferase differ in mRNA expression and enzymatic activity.''; PubMedEurope PMCScholia
Ou WJ, Cameron PH, Thomas DY, Bergeron JJ.; ''Association of folding intermediates of glycoproteins with calnexin during protein maturation.''; PubMedEurope PMCScholia
Peneff C, Ferrari P, Charrier V, Taburet Y, Monnier C, Zamboni V, Winter J, Harnois M, Fassy F, Bourne Y.; ''Crystal structures of two human pyrophosphorylase isoforms in complexes with UDPGlc(Gal)NAc: role of the alternatively spliced insert in the enzyme oligomeric assembly and active site architecture.''; PubMedEurope PMCScholia
Matthijs G, Schollen E, Pirard M, Budarf ML, Van Schaftingen E, Cassiman JJ.; ''PMM (PMM1), the human homologue of SEC53 or yeast phosphomannomutase, is localized on chromosome 22q13.''; PubMedEurope PMCScholia
Schallus T, Jaeckh C, Fehér K, Palma AS, Liu Y, Simpson JC, Mackeen M, Stier G, Gibson TJ, Feizi T, Pieler T, Muhle-Goll C.; ''Malectin: a novel carbohydrate-binding protein of the endoplasmic reticulum and a candidate player in the early steps of protein N-glycosylation.''; PubMedEurope PMCScholia
Angata K, Fukuda M.; ''Polysialyltransferases: major players in polysialic acid synthesis on the neural cell adhesion molecule.''; PubMedEurope PMCScholia
Grubenmann CE, Frank CG, Hülsmeier AJ, Schollen E, Matthijs G, Mayatepek E, Berger EG, Aebi M, Hennet T.; ''Deficiency of the first mannosylation step in the N-glycosylation pathway causes congenital disorder of glycosylation type Ik.''; PubMedEurope PMCScholia
Wang L, Liang Y, Li Z, Cai X, Zhang W, Wu G, Jin J, Fang Z, Yang Y, Zha X.; ''Increase in beta1-6 GlcNAc branching caused by N-acetylglucosaminyltransferase V directs integrin beta1 stability in human hepatocellular carcinoma cell line SMMC-7721.''; PubMedEurope PMCScholia
Wedgwood JF, Strominger JL.; ''Enzymatic activities in cultured human lymphocytes that dephosphorylate dolichyl pyrophosphate and dolichyl phosphate.''; PubMedEurope PMCScholia
Hull E, Sarkar M, Spruijt MP, Höppener JW, Dunn R, Schachter H.; ''Organization and localization to chromosome 5 of the human UDP-N-acetylglucosamine:alpha-3-D-mannoside beta-1,2-N-acetylglucosaminyltransferase I gene.''; PubMedEurope PMCScholia
Ohyama C, Smith PL, Angata K, Fukuda MN, Lowe JB, Fukuda M.; ''Molecular cloning and expression of GDP-D-mannose-4,6-dehydratase, a key enzyme for fucose metabolism defective in Lec13 cells.''; PubMedEurope PMCScholia
Kranz C, Jungeblut C, Denecke J, Erlekotte A, Sohlbach C, Debus V, Kehl HG, Harms E, Reith A, Reichel S, Grobe H, Hammersen G, Schwarzer U, Marquardt T.; ''A defect in dolichol phosphate biosynthesis causes a new inherited disorder with death in early infancy.''; PubMedEurope PMCScholia
Hardt B, Völker C, Mundt S, Salska-Navarro M, Hauptmann M, Bause E.; ''Human endo-alpha1,2-mannosidase is a Golgi-resident type II membrane protein.''; PubMedEurope PMCScholia
Schwarz M, Thiel C, Lübbehusen J, Dorland B, de Koning T, von Figura K, Lehle L, Körner C.; ''Deficiency of GDP-Man:GlcNAc2-PP-dolichol mannosyltransferase causes congenital disorder of glycosylation type Ik.''; PubMedEurope PMCScholia
Frank CG, Grubenmann CE, Eyaid W, Berger EG, Aebi M, Hennet T.; ''Identification and functional analysis of a defect in the human ALG9 gene: definition of congenital disorder of glycosylation type IL.''; PubMedEurope PMCScholia
Cantagrel V, Lefeber DJ, Ng BG, Guan Z, Silhavy JL, Bielas SL, Lehle L, Hombauer H, Adamowicz M, Swiezewska E, De Brouwer AP, Blümel P, Sykut-Cegielska J, Houliston S, Swistun D, Ali BR, Dobyns WB, Babovic-Vuksanovic D, van Bokhoven H, Wevers RA, Raetz CR, Freeze HH, Morava E, Al-Gazali L, Gleeson JG.; ''SRD5A3 is required for converting polyprenol to dolichol and is mutated in a congenital glycosylation disorder.''; PubMedEurope PMCScholia
Quirk S, Seley KL.; ''Substrate discrimination by the human GTP fucose pyrophosphorylase.''; PubMedEurope PMCScholia
Christianson JC, Shaler TA, Tyler RE, Kopito RR.; ''OS-9 and GRP94 deliver mutant alpha1-antitrypsin to the Hrd1-SEL1L ubiquitin ligase complex for ERAD.''; PubMedEurope PMCScholia
Züchner S, Dallman J, Wen R, Beecham G, Naj A, Farooq A, Kohli MA, Whitehead PL, Hulme W, Konidari I, Edwards YJ, Cai G, Peter I, Seo D, Buxbaum JD, Haines JL, Blanton S, Young J, Alfonso E, Vance JM, Lam BL, Peričak-Vance MA.; ''Whole-exome sequencing links a variant in DHDDS to retinitis pigmentosa.''; PubMedEurope PMCScholia
Lederkremer GZ.; ''Glycoprotein folding, quality control and ER-associated degradation.''; PubMedEurope PMCScholia
Thiel C, Schwarz M, Peng J, Grzmil M, Hasilik M, Braulke T, Kohlschütter A, von Figura K, Lehle L, Körner C.; ''A new type of congenital disorders of glycosylation (CDG-Ii) provides new insights into the early steps of dolichol-linked oligosaccharide biosynthesis.''; PubMedEurope PMCScholia
Wada Y, Sakamoto M.; ''Isolation of the human phosphomannomutase gene (PMM1) and assignment to chromosome 22q13.''; PubMedEurope PMCScholia
Montiel MD, Krzewinski-Recchi MA, Delannoy P, Harduin-Lepers A.; ''Molecular cloning, gene organization and expression of the human UDP-GalNAc:Neu5Acalpha2-3Galbeta-R beta1,4-N-acetylgalactosaminyltransferase responsible for the biosynthesis of the blood group Sda/Cad antigen: evidence for an unusual extended cytoplasmic domain.''; PubMedEurope PMCScholia
Burda P, Aebi M.; ''The ALG10 locus of Saccharomyces cerevisiae encodes the alpha-1,2 glucosyltransferase of the endoplasmic reticulum: the terminal glucose of the lipid-linked oligosaccharide is required for efficient N-linked glycosylation.''; PubMedEurope PMCScholia
Kranz C, Denecke J, Lehle L, Sohlbach K, Jeske S, Meinhardt F, Rossi R, Gudowius S, Marquardt T.; ''Congenital disorder of glycosylation type Ik (CDG-Ik): a defect of mannosyltransferase I.''; PubMedEurope PMCScholia
Intra J, Perotti ME, Pavesi G, Horner D.; ''Comparative and phylogenetic analysis of alpha-L-fucosidase genes.''; PubMedEurope PMCScholia
Song BL, Sever N, DeBose-Boyd RA.; ''Gp78, a membrane-anchored ubiquitin ligase, associates with Insig-1 and couples sterol-regulated ubiquitination to degradation of HMG CoA reductase.''; PubMedEurope PMCScholia
Wickramasinghe S, Medrano JF.; ''Primer on genes encoding enzymes in sialic acid metabolism in mammals.''; PubMedEurope PMCScholia
Kudo T, Nakagawa H, Takahashi M, Hamaguchi J, Kamiyama N, Yokoo H, Nakanishi K, Nakagawa T, Kamiyama T, Deguchi K, Nishimura S, Todo S.; ''N-glycan alterations are associated with drug resistance in human hepatocellular carcinoma.''; PubMedEurope PMCScholia
Nauseef WM, McCormick SJ, Clark RA.; ''Calreticulin functions as a molecular chaperone in the biosynthesis of myeloperoxidase.''; PubMedEurope PMCScholia
Furukawa T, Youssef EM, Yatsuoka T, Yokoyama T, Makino N, Inoue H, Fukushige S, Hoshi M, Hayashi Y, Sunamura M, Horii A.; ''Cloning and characterization of the human UDP-N-acetylglucosamine: alpha-1,3-D-mannoside beta-1,4-N-acetylglucosaminyltransferase IV-homologue (hGnT-IV-H) gene.''; PubMedEurope PMCScholia
Vleugels W, Schollen E, Foulquier F, Matthijs G.; ''Screening for OST deficiencies in unsolved CDG-I patients.''; PubMedEurope PMCScholia
Lubas WA, Spiro RG.; ''Evaluation of the role of rat liver Golgi endo-alpha-D-mannosidase in processing N-linked oligosaccharides.''; PubMedEurope PMCScholia
Kasapkara CS, Tümer L, Ezgü FS, Hasanoğlu A, Race V, Matthijs G, Jaeken J.; ''SRD5A3-CDG: a patient with a novel mutation.''; PubMedEurope PMCScholia
McKnight GL, Mudri SL, Mathewes SL, Traxinger RR, Marshall S, Sheppard PO, O'Hara PJ.; ''Molecular cloning, cDNA sequence, and bacterial expression of human glutamine:fructose-6-phosphate amidotransferase.''; PubMedEurope PMCScholia
Karaveg K, Siriwardena A, Tempel W, Liu ZJ, Glushka J, Wang BC, Moremen KW.; ''Mechanism of class 1 (glycosylhydrolase family 47) {alpha}-mannosidases involved in N-glycan processing and endoplasmic reticulum quality control.''; PubMedEurope PMCScholia
Tremblay LO, Herscovics A.; ''Characterization of a cDNA encoding a novel human Golgi alpha 1, 2-mannosidase (IC) involved in N-glycan biosynthesis.''; PubMedEurope PMCScholia
Angata K, Suzuki M, McAuliffe J, Ding Y, Hindsgaul O, Fukuda M.; ''Differential biosynthesis of polysialic acid on neural cell adhesion molecule (NCAM) and oligosaccharide acceptors by three distinct alpha 2,8-sialyltransferases, ST8Sia IV (PST), ST8Sia II (STX), and ST8Sia III.''; PubMedEurope PMCScholia
Schollen E, Dorland L, de Koning TJ, Van Diggelen OP, Huijmans JG, Marquardt T, Babovic-Vuksanovic D, Patterson M, Imtiaz F, Winchester B, Adamowicz M, Pronicka E, Freeze H, Matthijs G.; ''Genomic organization of the human phosphomannose isomerase (MPI) gene and mutation analysis in patients with congenital disorders of glycosylation type Ib (CDG-Ib).''; PubMedEurope PMCScholia
Sun L, Eklund EA, Chung WK, Wang C, Cohen J, Freeze HH.; ''Congenital disorder of glycosylation id presenting with hyperinsulinemic hypoglycemia and islet cell hyperplasia.''; PubMedEurope PMCScholia
Suzuki T, Yano K, Sugimoto S, Kitajima K, Lennarz WJ, Inoue S, Inoue Y, Emori Y.; ''Endo-beta-N-acetylglucosaminidase, an enzyme involved in processing of free oligosaccharides in the cytosol.''; PubMedEurope PMCScholia
Timson DJ, Reece RJ.; ''Identification and characterisation of human aldose 1-epimerase.''; PubMedEurope PMCScholia
Senderek J, Müller JS, Dusl M, Strom TM, Guergueltcheva V, Diepolder I, Laval SH, Maxwell S, Cossins J, Krause S, Muelas N, Vilchez JJ, Colomer J, Mallebrera CJ, Nascimento A, Nafissi S, Kariminejad A, Nilipour Y, Bozorgmehr B, Najmabadi H, Rodolico C, Sieb JP, Steinlein OK, Schlotter B, Schoser B, Kirschner J, Herrmann R, Voit T, Oldfors A, Lindbergh C, Urtizberea A, von der Hagen M, Hübner A, Palace J, Bushby K, Straub V, Beeson D, Abicht A, Lochmüller H.; ''Hexosamine biosynthetic pathway mutations cause neuromuscular transmission defect.''; PubMedEurope PMCScholia
Gao XD, Tachikawa H, Sato T, Jigami Y, Dean N.; ''Alg14 recruits Alg13 to the cytoplasmic face of the endoplasmic reticulum to form a novel bipartite UDP-N-acetylglucosamine transferase required for the second step of N-linked glycosylation.''; PubMedEurope PMCScholia
Sasaki N, Manya H, Okubo R, Kobayashi K, Ishida H, Toda T, Endo T, Nishihara S.; ''beta4GalT-II is a key regulator of glycosylation of the proteins involved in neuronal development.''; PubMedEurope PMCScholia
Takahashi S, Hori K, Takahashi K, Ogasawara H, Tomatsu M, Saito K.; ''Effects of nucleotides on N-acetyl-d-glucosamine 2-epimerases (renin-binding proteins): comparative biochemical studies.''; PubMedEurope PMCScholia
Yamaguchi Y, Ikeda Y, Takahashi T, Ihara H, Tanaka T, Sasho C, Uozumi N, Yanagidani S, Inoue S, Fujii J, Taniguchi N.; ''Genomic structure and promoter analysis of the human alpha1, 6-fucosyltransferase gene (FUT8).''; PubMedEurope PMCScholia
Wolf MJ, Rush JS, Waechter CJ.; ''Golgi-enriched membrane fractions from rat brain and liver contain long-chain polyisoprenyl pyrophosphate phosphatase activity.''; PubMedEurope PMCScholia
Clarke LA.; ''The mucopolysaccharidoses: a success of molecular medicine.''; PubMedEurope PMCScholia
Petrescu AJ, Milac AL, Petrescu SM, Dwek RA, Wormald MR.; ''Statistical analysis of the protein environment of N-glycosylation sites: implications for occupancy, structure, and folding.''; PubMedEurope PMCScholia
Harduin-Lepers A, Vallejo-Ruiz V, Krzewinski-Recchi MA, Samyn-Petit B, Julien S, Delannoy P.; ''The human sialyltransferase family.''; PubMedEurope PMCScholia
Cameron HS, Szczepaniak D, Weston BW.; ''Expression of human chromosome 19p alpha(1,3)-fucosyltransferase genes in normal tissues. Alternative splicing, polyadenylation, and isoforms.''; PubMedEurope PMCScholia
Matthijs G, Schollen E, Pardon E, Veiga-Da-Cunha M, Jaeken J, Cassiman JJ, Van Schaftingen E.; ''Mutations in PMM2, a phosphomannomutase gene on chromosome 16p13, in carbohydrate-deficient glycoprotein type I syndrome (Jaeken syndrome).''; PubMedEurope PMCScholia
Bergfeld AK, Pearce OM, Diaz SL, Pham T, Varki A.; ''Metabolism of vertebrate amino sugars with N-glycolyl groups: elucidating the intracellular fate of the non-human sialic acid N-glycolylneuraminic acid.''; PubMedEurope PMCScholia
Harada Y, Masahara-Negishi Y, Suzuki T.; ''Cytosolic-free oligosaccharides are predominantly generated by the degradation of dolichol-linked oligosaccharides in mammalian cells.''; PubMedEurope PMCScholia
O'Reilly MK, Zhang G, Imperiali B.; ''In vitro evidence for the dual function of Alg2 and Alg11: essential mannosyltransferases in N-linked glycoprotein biosynthesis.''; PubMedEurope PMCScholia
Pang H, Koda Y, Soejima M, Kimura H.; ''Identification of human phosphoglucomutase 3 (PGM3) as N-acetylglucosamine-phosphate mutase (AGM1).''; PubMedEurope PMCScholia
Alanen HI, Williamson RA, Howard MJ, Hatahet FS, Salo KE, Kauppila A, Kellokumpu S, Ruddock LW.; ''ERp27, a new non-catalytic endoplasmic reticulum-located human protein disulfide isomerase family member, interacts with ERp57.''; PubMedEurope PMCScholia
Kumar R, Yang J, Larsen RD, Stanley P.; ''Cloning and expression of N-acetylglucosaminyltransferase I, the medial Golgi transferase that initiates complex N-linked carbohydrate formation.''; PubMedEurope PMCScholia
Akama TO, Nakagawa H, Wong NK, Sutton-Smith M, Dell A, Morris HR, Nakayama J, Nishimura S, Pai A, Moremen KW, Marth JD, Fukuda MN.; ''Essential and mutually compensatory roles of {alpha}-mannosidase II and {alpha}-mannosidase IIx in N-glycan processing in vivo in mice.''; PubMedEurope PMCScholia
Kelleher DJ, Gilmore R.; ''An evolving view of the eukaryotic oligosaccharyltransferase.''; PubMedEurope PMCScholia
Hinderlich S, Berger M, Schwarzkopf M, Effertz K, Reutter W.; ''Molecular cloning and characterization of murine and human N-acetylglucosamine kinase.''; PubMedEurope PMCScholia
Oriol R, Martinez-Duncker I, Chantret I, Mollicone R, Codogno P.; ''Common origin and evolution of glycosyltransferases using Dol-P-monosaccharides as donor substrate.''; PubMedEurope PMCScholia
Chantret I, Dupré T, Delenda C, Bucher S, Dancourt J, Barnier A, Charollais A, Heron D, Bader-Meunier B, Danos O, Seta N, Durand G, Oriol R, Codogno P, Moore SE.; ''Congenital disorders of glycosylation type Ig is defined by a deficiency in dolichyl-P-mannose:Man7GlcNAc2-PP-dolichyl mannosyltransferase.''; PubMedEurope PMCScholia
Hansske B, Thiel C, Lübke T, Hasilik M, Höning S, Peters V, Heidemann PH, Hoffmann GF, Berger EG, von Figura K, Körner C.; ''Deficiency of UDP-galactose:N-acetylglucosamine beta-1,4-galactosyltransferase I causes the congenital disorder of glycosylation type IId.''; PubMedEurope PMCScholia
Granovsky M, Fata J, Pawling J, Muller WJ, Khokha R, Dennis JW.; ''Suppression of tumor growth and metastasis in Mgat5-deficient mice.''; PubMedEurope PMCScholia
Imbach T, Burda P, Kuhnert P, Wevers RA, Aebi M, Berger EG, Hennet T.; ''A mutation in the human ortholog of the Saccharomyces cerevisiae ALG6 gene causes carbohydrate-deficient glycoprotein syndrome type-Ic.''; PubMedEurope PMCScholia
Kämpf M, Absmanner B, Schwarz M, Lehle L.; ''Biochemical characterization and membrane topology of Alg2 from Saccharomyces cerevisiae as a bifunctional alpha1,3- and 1,6-mannosyltransferase involved in lipid-linked oligosaccharide biosynthesis.''; PubMedEurope PMCScholia
Mi Y, Fiete D, Baenziger JU.; ''Ablation of GalNAc-4-sulfotransferase-1 enhances reproduction by altering the carbohydrate structures of luteinizing hormone in mice.''; PubMedEurope PMCScholia
Tian H, Miyoshi E, Kawaguchi N, Shaker M, Ito Y, Taniguchi N, Tsujimoto M, Matsuura N.; ''The implication of N-acetylglucosaminyltransferase V expression in gastric cancer.''; PubMedEurope PMCScholia
Serafini-Cessi F, Conte R.; ''Precipitin reaction between Sda-active human Tamm-Horsfall glycoprotein and anti-Sda-serum.''; PubMedEurope PMCScholia
Takahashi T, Honda R, Nishikawa Y.; ''Cloning of the human cDNA which can complement the defect of the yeast mannosyltransferase I-deficient mutant alg 1.''; PubMedEurope PMCScholia
Maeda Y, Tanaka S, Hino J, Kangawa K, Kinoshita T.; ''Human dolichol-phosphate-mannose synthase consists of three subunits, DPM1, DPM2 and DPM3.''; PubMedEurope PMCScholia
Hiraoka N, Misra A, Belot F, Hindsgaul O, Fukuda M.; ''Molecular cloning and expression of two distinct human N-acetylgalactosamine 4-O-sulfotransferases that transfer sulfate to GalNAc beta 1-->4GlcNAc beta 1-->R in both N- and O-glycans.''; PubMedEurope PMCScholia
Tonetti M, Sturla L, Bisso A, Benatti U, De Flora A.; ''Synthesis of GDP-L-fucose by the human FX protein.''; PubMedEurope PMCScholia
Gonzalez DS, Karaveg K, Vandersall-Nairn AS, Lal A, Moremen KW.; ''Identification, expression, and characterization of a cDNA encoding human endoplasmic reticulum mannosidase I, the enzyme that catalyzes the first mannose trimming step in mammalian Asn-linked oligosaccharide biosynthesis.''; PubMedEurope PMCScholia
Arnold SM, Kaufman RJ.; ''The noncatalytic portion of human UDP-glucose: glycoprotein glucosyltransferase I confers UDP-glucose binding and transferase function to the catalytic domain.''; PubMedEurope PMCScholia
Saxena A, Yik JH, Weigel PH.; ''H2, the minor subunit of the human asialoglycoprotein receptor, trafficks intracellularly and forms homo-oligomers, but does not bind asialo-orosomucoid.''; PubMedEurope PMCScholia
Clarke JL, Watkins WM.; ''Expression of human alpha-l-fucosyltransferase gene homologs in monkey kidney COS cells and modification of potential fucosyltransferase acceptor substrates by an endogenous glycosidase.''; PubMedEurope PMCScholia
Ide Y, Miyoshi E, Nakagawa T, Gu J, Tanemura M, Nishida T, Ito T, Yamamoto H, Kozutsumi Y, Taniguchi N.; ''Aberrant expression of N-acetylglucosaminyltransferase-IVa and IVb (GnT-IVa and b) in pancreatic cancer.''; PubMedEurope PMCScholia
Cipollo JF, Trimble RB, Chi JH, Yan Q, Dean N.; ''The yeast ALG11 gene specifies addition of the terminal alpha 1,2-Man to the Man5GlcNAc2-PP-dolichol N-glycosylation intermediate formed on the cytosolic side of the endoplasmic reticulum.''; PubMedEurope PMCScholia
Apweiler R, Hermjakob H, Sharon N.; ''On the frequency of protein glycosylation, as deduced from analysis of the SWISS-PROT database.''; PubMedEurope PMCScholia
Kinoshita T, Inoue N.; ''Dissecting and manipulating the pathway for glycosylphos-phatidylinositol-anchor biosynthesis.''; PubMedEurope PMCScholia
Lo Presti L, Cabuy E, Chiricolo M, Dall'Olio F.; ''Molecular cloning of the human beta1,4 N-acetylgalactosaminyltransferase responsible for the biosynthesis of the Sd(a) histo-blood group antigen: the sequence predicts a very long cytoplasmic domain.''; PubMedEurope PMCScholia
Alcock F, Swanton E.; ''Mammalian OS-9 is upregulated in response to endoplasmic reticulum stress and facilitates ubiquitination of misfolded glycoproteins.''; PubMedEurope PMCScholia
Schaub BE, Berger B, Berger EG, Rohrer J.; ''Transition of galactosyltransferase 1 from trans-Golgi cisterna to the trans-Golgi network is signal mediated.''; PubMedEurope PMCScholia
Schmid M, Prajczer S, Gruber LN, Bertocchi C, Gandini R, Pfaller W, Jennings P, Joannidis M.; ''Uromodulin facilitates neutrophil migration across renal epithelial monolayers.''; PubMedEurope PMCScholia
Misago M, Liao YF, Kudo S, Eto S, Mattei MG, Moremen KW, Fukuda MN.; ''Molecular cloning and expression of cDNAs encoding human alpha-mannosidase II and a previously unrecognized alpha-mannosidase IIx isozyme.''; PubMedEurope PMCScholia
Ciccarelli FD, von Mering C, Suyama M, Harrington ED, Izaurralde E, Bork P.; ''Complex genomic rearrangements lead to novel primate gene function.''; PubMedEurope PMCScholia
Zhou H, Sun L, Li J, Xu C, Yu F, Liu Y, Ji C, He J.; ''The crystal structure of human GDP-L-fucose synthase.''; PubMedEurope PMCScholia
Pinho SS, Reis CA, Paredes J, Magalhães AM, Ferreira AC, Figueiredo J, Xiaogang W, Carneiro F, Gärtner F, Seruca R.; ''The role of N-acetylglucosaminyltransferase III and V in the post-transcriptional modifications of E-cadherin.''; PubMedEurope PMCScholia
Willems PJ, Seo HC, Coucke P, Tonlorenzi R, O'Brien JS.; ''Spectrum of mutations in fucosidosis.''; PubMedEurope PMCScholia
Sar1p-GTP recruits the cytoplasmic Sec23p-Sec24p complex. Though not represented in the subsequent steps, Sec23p-Sec24p would bind to members of the p24 protein family of possible cargo receptors, and together with Sar1p bind the appropiate v-SNARE, and Rab-GTP.
Sar1p-GTP hydrolysis is increased 15-30-fold by Sec23p. Sar1p-GDP is released as a result of this hydrolysis and used in further vesicle sculpting cycles. Sar1p-GTP hydrolysis occurs at two critical points during the cycle, first (as represented here) as a proofreading step, insuring that the cargo is loaded. Later in the cycle Sar1p-GTP hydrolysis triggers the uncoating of the budded vesicle.
Cytosolic GDP-mannose reacts with dolichyl phosphate in the endoplasmic reticulum membrane to form dolichyl phosphate D-mannose. The reaction is catalyzed by dolichyl-phosphate mannosyltransferase, a heterotrimeric protein embedded in the endoplasmic reticulum membrane. The first subunit of the heterotrimer appears to be the actual catalyst, and the other two subunits appear to stabilize it (Maeda et al. 2000).
In the last step of the N-glycan precursor biosynthesis pathway, the mature N-glycan (Glc3Man9GlcNAc2) is removed from the dolichyl diphosphate molecule upon which it has been synthesized, and attached to a nascent protein. In this process, a dolichyl diphosphate molecule is released and once de-phosphorylated by dolichyl diphosphatase 1 (DOLPP1) to obtain dolichyl phosphate, it can be used as a substrate for the synthesis of another N-glycan oligosaccharide (Wedgwood JF and Strominger JL, 1980).
Glucosamine-fructose 6-phosphate aminotransferase (GFAT) is the first and rate-limiting enzyme in the hexosamine synthesis pathway, and thus formation of hexosamines like N-acetylglucosamine (GlcNAc). This enzyme probably plays a role in limiting the availability of substrates for the N- and O- linked glycosylation of proteins. Two isoforms, GFAT 1 and 2, have been identified (McKnight GL et al, 1992; Oki T et al, 1999). GFAT is required normal functioning of neuromuscular synaptic transmission. Defects in the gene expressing this protein leads to altered muscle fiber morphology and impaired neuromuscular junction development (Senderek et al, 2011).
Dolichyl-phosphate beta-glucosyltransferase (ALG5) associated with the endoplasmic reticulum (ER) membrane catalyzes the reaction of cytosolic UDP-glucose with dolichyl phosphate exposed on the cytosolic face of the ER membrane to form Dolichyl-P-glucose with its glucose moiety oriented toward the cytosol (Imbach T et al, 1999).
In the first step of N-glycan precursor (LLO) synthesis, N-acetylglucosamine is added, via an alpha-1,3 linkage, to a molecule of dolichyl phosphate, producing N-acetyl-D-glucosaminyl-diphosphodolichol (Eckert V et al, 1998). This reaction is catalyzed by DPAGT1 (ALG7 in yeast), mutations in which are associated with CDG disorder type I-J (Wu X et al, 2003). The dolichyl phosphate acts as an anchor for the LLO, so the following sugar-addition reactions take place on a sugar anchored in the ER membrane.
A mannose is added to the N-glycan precursor via a beta-1,4 linkage. The reaction is catalyzed by ALG1 (Takahashi T et al, 2000). Defects in ALG1 lead to congenital disorder of glycosylation type 1K (CDG1K) (Schwarz M et al, 2004; Kranz C et al, 2004; Grubenmann CE et al, 2004).
Cytosolic GNPNAT1 catalyzes the reaction of glucosamine 6-phosphate and acetyl-CoA to form N-acetyl-glucosamine 6-phosphate (GlcNAc6P) and CoA-SH. Structural studies indicate that the active form of the enzyme is a dimer (Wang J et al, 2008).
Dolichyl-phosphate-glucose is flipped toward the luminal side of the ER membrane (Imbach T et al, 1999). The exact mechanism and proteins involved in this step are not clear yet, but it is known that it must be carried out by a different flippase than the one that catalyzes the flipping of the N-glycan precursor (Sanyal S et al, 2008).
Mannose 1-phosphate is converted to GDP-Mannose by mannose-1-phosphate guanyltransferase alpha and beta forms (GMPPA/B). This enzyme had originally been characterized from rat and bovine sources (Verachtert H et al, 1966) and more recently from pig (Ning B and Elbein AD, 2000).
The precursor of the N-glycan sugar, now in the form of (GlcNAc)2 (Man)5 (PP-Dol), is flipped across the ER membrane, moving it from the cytosolic side into the ER lumen. The exact mechanism of this translocation is not well understood: the protein RFT1 is known to be involved (Helenius et al, 2002), along with an unknown flippase, which is distinct from the one that flips the Dol-P linked precursors (Dol-P-Mannose and Dol-P-glucose) (Sanyal et al, 2008). Defects in RFT1 are associated with Congenital Disorder of Glycosylation 1N (CDG1N) (Haeuptle MA et al, 2008).
Cytosolic PGM3 catalyzes the isomerization of N-acetyl-D-glucosamine 6-phosphate (GlcNAc6P) to form N-acetyl-D-glucosamine 1-phosphate (GlcNAc1P) (Pang H et al, 2002).
The phosphorylation of a dolichol residue of the ER membrane is a starting step in the N-glycan biosynthesis pathway (Fernandez F et al, 2002). Defects in DOLK are the cause of congenital disorder of glycosylation type 1M (CDG1M), also known as dolichol kinase deficiency (Kranz C et al, 2007).
A second N-acetylglucosamine is added to the N-glycan precursor via a beta-1,4 linkage. This reaction is catalyzed by the ALG13:ALG14 complex, in which ALG13 functions as the catalyst and ALG14 functions as a membrane anchor which recruits ALG13 to the cytosolic face of ER (Gao XD et al, 2005).
A second mannose is added to the N-glycan precursor via an alpha-1,3 linkage. The reaction is catalyzed by the mannosyltransferase ALG2. This is a bifunctional enzyme with both alpha 1,3- and alpha 1,6-mannosyltransferase activities. In humans, only the alpha 1,3 activity used in this reaction has been elucidated (Thiel C et al, 2003). Defects in ALG2 are the cause of CDG1I (Thiel C et al, 2003).
Mannose-6-phosphate isomerase (MPI) converts Fructose 6-phosphate to Mannose 6-phosphate (Proudfoot AE et al, 1994). Defects in this gene are associated with congenital disorder of glycosylation type 1B (CDG1B). Oral administration of mannose is an efficient therapy against this defect (Schollen E et al, 2000).
Cytosolic UAP1 catalyzes the reaction of N-acetyl-D-glucosamine 1-phosphate (GlcNAc1P) and UTP to UDP-N-acetyl-D-glucosamine and pyrophosphate. Structural studies indicate that the active form of the enzyme is a dimer (Peneff C et al, 2001).
Phosphomannomutase 1 and 2 (PMM1 and PMM2) catalyze the isomerization of Mannose 6-phosphate to Mannose 1-phosphate (Wada Y and Sakamoto M et al, 1997; Matthijs G et al, February 1997). Mutations in the PMM2 gene are one of the causes of Jaeken syndrome. a disease of glycosylation, type CDGIa. (Matthijs G et al, May 1997).
Calnexin (membrane protein) and calreticulin (soluble in ER) are two lectins (proteins that can bind a glycan) which recognize the mono-glucosylated form of the N-glycan and mediate the folding of the glycoproteins to which they are attached to (Ou WJ et al, 1993; Nauseef Wm et al, 1995). Calmegin is another chaperone with the same role expressed only in testis (van Lith M et al, 2007). These lectins act as chaperons, providing a protected environment where the unfolded glycoprotein can fold without forming interactions with other proteins or components in the ER. The unfolded protein can loop between these two steps multiple time, therefore this process is called the 'calnexin/calreticulin cycle'. If the protein achieves correct folding, it is modified by Mannosidase I and then moved to the cis-Golgi where the glycan is further processed.
A recently discovered protein called malectin is known to recognize the Glc(2)Man(9)GlcNAc(2) glycan (Schallus T et al, 2008). The exact role of this interaction is not clear but malectin is thought to regulate the availability of this substrate to glucosidase II, or to act as a chaperone to stabilize the unfolded protein.
While the protein is bound to the chaperone complex, the glycan is still accessible to glucosidase II, which eventually removes the last remaining glucose residue. This also results in breaking the interaction between the chaperone and the glycoprotein, independently of whether the latter has achieved proper folding (Pelletier MF et al, 2000). This has been interpreted as a 'timing mechanism', in which a protein has only a limited period of time to achieve correct folding when bound to the chaperone, to avoid the scenario where proteins that take too long to fold would block the availability of CNX or CRT. Proteins with folding defects get transported to the Endoplasmic Reticulum Quality Control Compartment, while proteins with correct folding are transported to the cis-Golgi where the glycan is further modified.
ERp57/ERp27 is a thiol-oxidoreductase that interacts with calnexin and mediates the formation of disulfide bonds in the unfolded glycoprotein (Alanen HI et al, 2006).
A second glucose is removed from the N-linked glycan. The removal of an alpha1,3 glucose moiety is catalyzed by glucosidase II, a complex composed of an alpha subunit (GANAB) with catalytic activity and a beta subunit (GLU2B; PRKCSH), probably with regulatory and recruitment function (Pelletier MF et al, 2000). GANAB can exist in two different isoforms, but both are able to catalyze both of the reactions catalyzed by glucosidase II (Pelletier MF et al, 2000). Defects in PRKCSH are a cause of polycystic liver disease (PCLD).
After the glycosylated precursor is attached to the protein, the outer alpha-1,2-linked glucose is removed by glucosidase I (MOGS, GCS1 in yeast). This is a mandatory step for the protein folding control and glycan extension, and defects in MOGS are associated with congenital disorder of glycosylation type IIb (CDGIIb) (De Praeter CM et al, 2000; Völker C et al, 2002).
Correctly folded proteins, after being released from the Calnexin/Calreticulin cycle, are translocated to the Golgi (Hauri H et al, 2000; Hauri HP et al, 2002; Molinari, 2007).
Addition of sialic acid to galactose-containing N-glycan. Sialic acid is usually found at terminal positions of the N-glycan. This imparts a negative charge at neutral pH this adds a negative charge which affects the chemico-physical and biological properties of the N-glycans (for a review, see Schauer R 2000); moreover, this modification can lead to the addition of extraordinarily long antennae such as polysialic acid (hundreds of sials) or poly lactosamine repeats (dozens of disaccharide repeats) (Harduin-Lepers A, 2001), while the number of modifications on the antennae of N-glycans is usually lower. There are over 20 sialyltransferases known in humans, 5 of which are known to act on N-glycans. ST6Gal I (ST6GAL1) is the only alpha-2,6-sialyltransferase known to transfer sialic acid to galactose on N-Glycans (Dall'Olio F, 2000). A second beta-Galactoside alpha-2,6-sialyltransferase has been characterized, but this enzyme acts mainly on oligosaccharides (Krzewinski-Recchi MA et al 2003). Sialic acids can also be added via an alpha-2,3-linkage to galactose on N-glycans by ST3GalIV(ST3GAL4) (Ellies et al 2002). ST8Sia II (ST8SIA2), ST8Sia III (ST8SIA3), and ST8Sia IV (ST8SIA6) have alpha-2,8-activity (Angata K et al 1997; Angata et al 2000; Angata K, Fuduka M 2003).
The enzyme ER Man I can slowly trim up to four of the mannoses on the N-glycan on unfolded proteins accumulated in the ER. This step describes the removal of the mannose in the B position (Gonzalez et al, 1999: Hirao et al, 2006).
The addition of a bisecting GlcNAc to a complex N-glycan by MGAT3 is one of the most important regulatory steps in N-glycosylation, directing the pathway toward the synthesis of complex and hybrid N-glycans. This addition changes the structure of the N-glycan and inhibits further modification by MGAT2, MGAT4, MGAT5A/B and FUT8. Defects in MGAT3 have been shown to be associated with predisposition to cancer and several developmental defects (Song et al 2010; Stanley 2002).
N-acetylglucosaminyltransferase (GnT)-IV catalyzes the addition of GlcNAc beta,1,4 on the GlcNAc beta1,2 Man,alpha1,3 arm of both complex and hybrid N-glycans (Oguri S et al, 2006). Two human GnT-IV isozymes have been characterized (MGAT4A, MGAT4B) , plus a putative MGAT4C on chromosome 2 (Furukawa T et al, 1999). Aberrant expression of MGAT4A or MGAT4B is associated with pancreatic cancer (Ide Y et al, 2006; Kudo T et al , 2007)
The removal of mannoses on the alpha,1,6 arm by MAN2A1 or MAN2A2 is required for efficient formation of complex-type N-glycans (Misago M et al, 1995; Crispin M et al, 2007). These two enzymes carry out the same function and the disruption of both inhibits the formation of complex N-glycans in vivo (Akama TO et al, 2006).
The enzyme ER Man I can slowly trim up to four of the mannoses on the N-glycan on unfolded proteins accumulated in the ER. This step describes the removal of the mannose in the A position (Hirao et al, 2006; Frenkel et al, 2003).
Addition of sialic acid to galactose-containing N-glycan. Sialic acid is usually found at terminal positions of the N-glycan. This imparts a negative charge at neutral pH this adds a negative charge which affects the chemico-physical and biological properties of the N-glycans (for a review, see Schauer R 2000); moreover, this modification can lead to the addition of extraordinarily long antennae such as polysialic acid (hundreds of sials) or poly lactosamine repeats (dozens of disaccharide repeats) (Harduin-Lepers A, 2001), while the number of modifications on the antennae of N-glycans is usually lower. There are over 20 sialyltransferases known in humans, 5 of which are known to act on N-glycans. ST6Gal I (ST6GAL1) is the only alpha-2,6-sialyltransferase known to transfer sialic acid to galactose on N-Glycans (Dall'Olio F, 2000). A second beta-Galactoside alpha-2,6-sialyltransferase has been characterized, but this enzyme acts mainly on oligosaccharides (Krzewinski-Recchi MA et al 2003). Sialic acids can also be added via an alpha-2,3-linkage to galactose on N-glycans by ST3GalIV(ST3GAL4) (Ellies et al 2002). ST8Sia II (ST8SIA2), ST8Sia III (ST8SIA3), and ST8Sia IV (ST8SIA6) have alpha-2,8-activity (Angata K et al 1997; Angata et al 2000; Angata K, Fuduka M 2003).
Addition of sialic acid to galactose-containing N-glycan. Sialic acid is usually found at terminal positions of the N-glycan. This imparts a negative charge at neutral pH this adds a negative charge which affects the chemico-physical and biological properties of the N-glycans (for a review, see Schauer R 2000); moreover, this modification can lead to the addition of extraordinarily long antennae such as polysialic acid (hundreds of sials) or poly lactosamine repeats (dozens of disaccharide repeats) (Harduin-Lepers A, 2001), while the number of modifications on the antennae of N-glycans is usually lower. There are over 20 sialyltransferases known in humans, 5 of which are known to act on N-glycans. ST6Gal I (ST6GAL1) is the only alpha-2,6-sialyltransferase known to transfer sialic acid to galactose on N-Glycans (Dall'Olio F, 2000). A second beta-Galactoside alpha-2,6-sialyltransferase has been characterized, but this enzyme acts mainly on oligosaccharides (Krzewinski-Recchi MA et al 2003). Sialic acids can also be added via an alpha-2,3-linkage to galactose on N-glycans by ST3GalIV(ST3GAL4) (Ellies et al 2002). ST8Sia II (ST8SIA2), ST8Sia III (ST8SIA3), and ST8Sia IV (ST8SIA6) have alpha-2,8-activity (Angata K et al 1997; Angata et al 2000; Angata K, Fuduka M 2003).
The enzyme ER Man I can slowly trim up to four of the mannoses on the N-glycan on unfolded proteins accumulated in the ER. This step describes the removal of the mannose in the C position (Hirao et al, 2006).
Cells exposed to castanospermine or 1-deoxynojirimycin (inhibitors of the glucosidase enzymes GCS1 and GANAB), are still able to carry out glycosylation and produce complex glycans. This is due to the existence of an alternative route catalyzed by the enzyme endomannosidase (Moore and Spiro, 1990). Glycoproteins that pass through this route probably skip or have a reduced interaction with the Calnexin/Calreticulin cycle, and are transported to the cis-golgi through a route that has not been described yet (probably through the general ER to Golgi flow). Here, the Endomannosidase enzyme, which resides on the Golgi membrane (Hardt et al 2005; Hamilton et al 2005) is able to remove the tri-, di-, or mono-glucose substituted mannose on branch A, leading to a deglucosylated N-glycan structure (Lubas and Spiro, 1988).
The LMAN1(also known as ERGIC-53)/MCFD2 complex recognizes Man8 and Man9 N-glycans released by the Calnexin/Calreticulin cycle and mediate their transport to the Golgi (Nyefeler B et al, 2003; Zhang B et al, 2003). Man8 glycan transfer is shown here.
Addition of a galactose residue on N-acetylglucosamine. The family of beta 4-galactosyltransferases is composed by at least six known members with different K(m) and acceptor specifities (Guo S et al, 2001) and probably originated by duplication (Lo NW et al, 1998). B4GALT1 is associated with Congenital Disorder of Glycosylation of type IId (Hansske B et al, 2002), and is expressed as two splicing isoforms of which only one is localizated in the Golgi system (Lopez LC et al, 1991; Schaub BE et al, 2006). B4GALT2 is key in the regulation of proteins involved in neuronal development (Sasaki N et al, 2005).
In the cis-Golgi, Man7, Man8 or Man9 N-glycans are progressively trimmed to Man5 N-glycans. The reaction can be catalyzed by one of three known mannosidases, expressed in different tissues and with slightly different affinity. These enzymes trim the mannoses in a different order (Tremblay and Herscovics, 2000), but produce the same output with 5 mannoses. A small confusion on the nomenclature of these genes coding for these enzymes is present in the literature: the standard HGNC symbols are MAN1A1, MAN1A2, MAN1C1, but MAN1A2 is also referred to as MAN1B in certain publications, while MAN1B1 is the enzyme acting in the ERQC compartment on unfolded glycoproteins. Moreover, the names do not correspond to a preference of these enzymes for which of the three mannose branches these trim first.
Proteins with major folding defects are extracted from futile folding cycles in the calnexin chaperone system and the ER Quality Control Compartment, and are translocated back to the citosol for degradation. The N-glycan is used as a signal to distinguish proteins to be degraded, upon recognition by EDEM1, EDEM2 and EDEM3, three ER-stress-induced members of the glycosyl hydrolase 47 family (see Olivari S, Molinari M 2007 for a review) and OS9 (Mikami K, 2010; Hosokawa N, 2009).
In the cis-Golgi, Man7, Man8 or Man9 N-glycans are progressively trimmed to Man5 N-glycans. The reaction can be catalyzed by one of three known mannosidases, expressed in different tissues and with slightly different affinity. These enzymes trim the mannoses in a different order (Tremblay and Herscovics, 2000), but produce the same output with 5 mannoses. A small confusion on the nomenclature of these genes coding for these enzymes is present in the literature: the standard HGNC symbols are MAN1A1, MAN1A2, MAN1C1, but MAN1A2 is also referred to as MAN1B in certain publications, while MAN1B1 is the enzyme acting in the ERQC compartment on unfolded glycoproteins. Moreover, the names do not correspond to a preference of these enzymes for which of the three mannose branches these trim first.
N-acetylglucosaminyltransferase (GnT)-V catalyzes the addition of GlcNAc beta 1,4 on the GlcNAc beta1,2 Man,alpha1,6 arm of complex type N-Glycans (Park C et al, 1999; Granowski M et al, 2000; Wang L et al, 2007). The activity of MGAT5 competes with MGAT3 (Pinho SS et al, 2009) and is associated with gastric cancer (Tian H et al, 2008) and multiple sclerosis (Brynedal B et al, 2010).
In the cis-Golgi, Man7, Man8 or Man9 N-glycans are progressively trimmed to Man5 N-glycans. The reaction can be catalyzed by one of three known mannosidases, expressed in different tissues and with slightly different affinity. These enzymes trim the mannoses in a different order (Tremblay and Herscovics, 2000), but produce the same output with 5 mannoses. A small confusion on the nomenclature of these genes coding for these enzymes is present in the literature: the standard HGNC symbols are MAN1A1, MAN1A2, MAN1C1, but MAN1A2 is also referred to as MAN1B in certain publications, while MAN1B1 is the enzyme acting in the ERQC compartment on unfolded glycoproteins. Moreover, the names do not correspond to a preference of these enzymes for which of the three mannose branches these trim first.
Addition of a fucose moiety as an alpha 1-6 linkage to the first GlcNAc residue of the N-glycan (Clarke JL, Watkins WM 1999; Yamaguchi Y et al, 1999; Yamaguchi Y et al 2000).
Dolichyl phosphate D-mannose is flipped in the endoplasmic reticulum membrane so that its mannose moiety is oriented inwards, towards the endoplasmic reticulum lumen, where it is accessible to transferases catalyzing the synthesis of glycolipids and glycoproteins (Kinoshita and Inoue 2000).
The addition of an N-glycan to a protein can have several roles (Shental-Bechor D and Levy Y, 2009). First, glycans enhance the solubility and stability of the proteins in the ER, the golgi and on the outside of the cell membrane, where the composition of the medium is strongly hydrophilic and where proteins, that are mostly hydrophobic, have difficulty folding properly. Second, N-glycans are used as signal molecules during the folding and transport process of the protein: they have the role of labels to determine when a protein must interact with a chaperon, be transported to the golgi, or targeted for degradation in case of major folding defects. Third, and most importantly, N-glycans on completely folded proteins are involved in a wide range of processes: they help determine the specificity of membrane receptors in innate immunity or in cell-to-cell interactions, they can change the properties of hormones and secreted proteins, or of the proteins in the vesicular system inside the cell.
All N-linked glycans are derived from a common 14-sugar oligosaccharide synthesized in the ER, which is attached co-translationally to a protein while this is being translated inside the reticulum. The process of the synthesis of this glycan, known as Synthesis of the N-glycan precursor or LLO, constitutes one of the most conserved pathways in eukaryotes, and has been also observed in some eubacteria. The attachment usually happens on an asparagine residue within the consensus sequence asparagine-X-threonine by an complex called oligosaccharyl transferase (OST).
After being attached to an unfolded protein, the glycan is used as a label molecule in the folding process (also known as Calnexin/Calreticulin cycle) (Lederkremer GZ, 2009). The majority of the glycoproteins in the ER require at least one glycosylated residue in order to achieve proper folding, even if it has been shown that a smaller portion of the proteins in the ER can be folded without this modification.
Once the glycoprotein has achieved proper folding, it is transported via the Cis-golgi through all the Golgi compartments, where the glycan is further modified according to the properties of the glycoprotein. This process involves relatively few enzymes but due to its combinatorial nature, can lead to several millions of different possible modifications. The exact topography of this network of reactions has not been established yet, representing one of the major challenges after the sequencing of the human genome (Hossler P et al, 2006).
Since N-glycosylation is involved in an great number of different processes, from cell-cell interaction to folding control, mutations in one of the genes involved in glycan assembly and/or modification can lead to severe development problems (often affecting the central nervous system). All the diseases in genes involved in glycosylation are collectively known as Congenital Disorders of Glycosylation (CDG) (Sparks SE et al, 2003), and classified as CDG type I for the genes in the LLO synthesis pathway, and CDG type II for the others.
Original Pathway at Reactome: http://www.reactome.org/PathwayBrowser/#DB=gk_current&FOCUS_SPECIES_ID=48887&FOCUS_PATHWAY_ID=446203
Try the New WikiPathways
View approved pathways at the new wikipathways.org.Quality Tags
Ontology Terms
Bibliography
History
External references
DataNodes
GTP Sec23p Sec24p Sec13p
Sec31p ComplexGTP Sec23p
Sec24pSec23p Sec24p Sec13p
Sec31p Complexglycan chaperone
ERp57Annotated Interactions
There are over 20 sialyltransferases known in humans, 5 of which are known to act on N-glycans. ST6Gal I (ST6GAL1) is the only alpha-2,6-sialyltransferase known to transfer sialic acid to galactose on N-Glycans (Dall'Olio F, 2000). A second beta-Galactoside alpha-2,6-sialyltransferase has been characterized, but this enzyme acts mainly on oligosaccharides (Krzewinski-Recchi MA et al 2003). Sialic acids can also be added via an alpha-2,3-linkage to galactose on N-glycans by ST3GalIV(ST3GAL4) (Ellies et al 2002). ST8Sia II (ST8SIA2), ST8Sia III (ST8SIA3), and ST8Sia IV (ST8SIA6) have alpha-2,8-activity (Angata K et al 1997; Angata et al 2000; Angata K, Fuduka M 2003).
There are over 20 sialyltransferases known in humans, 5 of which are known to act on N-glycans. ST6Gal I (ST6GAL1) is the only alpha-2,6-sialyltransferase known to transfer sialic acid to galactose on N-Glycans (Dall'Olio F, 2000). A second beta-Galactoside alpha-2,6-sialyltransferase has been characterized, but this enzyme acts mainly on oligosaccharides (Krzewinski-Recchi MA et al 2003). Sialic acids can also be added via an alpha-2,3-linkage to galactose on N-glycans by ST3GalIV(ST3GAL4) (Ellies et al 2002). ST8Sia II (ST8SIA2), ST8Sia III (ST8SIA3), and ST8Sia IV (ST8SIA6) have alpha-2,8-activity (Angata K et al 1997; Angata et al 2000; Angata K, Fuduka M 2003).
There are over 20 sialyltransferases known in humans, 5 of which are known to act on N-glycans. ST6Gal I (ST6GAL1) is the only alpha-2,6-sialyltransferase known to transfer sialic acid to galactose on N-Glycans (Dall'Olio F, 2000). A second beta-Galactoside alpha-2,6-sialyltransferase has been characterized, but this enzyme acts mainly on oligosaccharides (Krzewinski-Recchi MA et al 2003). Sialic acids can also be added via an alpha-2,3-linkage to galactose on N-glycans by ST3GalIV(ST3GAL4) (Ellies et al 2002). ST8Sia II (ST8SIA2), ST8Sia III (ST8SIA3), and ST8Sia IV (ST8SIA6) have alpha-2,8-activity (Angata K et al 1997; Angata et al 2000; Angata K, Fuduka M 2003).
Glycoproteins that pass through this route probably skip or have a reduced interaction with the Calnexin/Calreticulin cycle, and are transported to the cis-golgi through a route that has not been described yet (probably through the general ER to Golgi flow). Here, the Endomannosidase enzyme, which resides on the Golgi membrane (Hardt et al 2005; Hamilton et al 2005) is able to remove the tri-, di-, or mono-glucose substituted mannose on branch A, leading to a deglucosylated N-glycan structure (Lubas and Spiro, 1988).
al, 2005).
A small confusion on the nomenclature of these genes coding for these enzymes is present in the literature: the standard HGNC symbols are MAN1A1, MAN1A2, MAN1C1, but MAN1A2 is also referred to as MAN1B in certain publications, while MAN1B1 is the enzyme acting in the ERQC compartment on unfolded glycoproteins. Moreover, the names do not correspond to a preference of these enzymes for which of the three mannose branches these trim first.
A small confusion on the nomenclature of these genes coding for these enzymes is present in the literature: the standard HGNC symbols are MAN1A1, MAN1A2, MAN1C1, but MAN1A2 is also referred to as MAN1B in certain publications, while MAN1B1 is the enzyme acting in the ERQC compartment on unfolded glycoproteins. Moreover, the names do not correspond to a preference of these enzymes for which of the three mannose branches these trim first.
A small confusion on the nomenclature of these genes coding for these enzymes is present in the literature: the standard HGNC symbols are MAN1A1, MAN1A2, MAN1C1, but MAN1A2 is also referred to as MAN1B in certain publications, while MAN1B1 is the enzyme acting in the ERQC compartment on unfolded glycoproteins. Moreover, the names do not correspond to a preference of these enzymes for which of the three mannose branches these trim first.
residue of the N-glycan (Clarke JL, Watkins WM 1999; Yamaguchi Y et
al, 1999; Yamaguchi Y et al 2000).
GTP Sec23p
Sec24pGTP Sec23p
Sec24pSec23p Sec24p Sec13p
Sec31p Complex