In vivo synthesis of complex N-glycans by expression of human N-acetylglucosaminyltransferase I in the filamentous fungus Trichoderma reesei (original) (raw)
European Journal of Biochemistry, 1997
To investigate the potential of filamentous fungi to synthesize N-glycans that are convertible to a mammalian type, in vitro glycosylation assays were performed. Recombinant human N-acetylglucosaminyltransferase I, human p-1,4-galactosyltransferase and rat a-2,6-sialyltransferase were successively used to mimic part of the mammalian glycosylation synthesis pathway. High-mannose carbohydrates on Trickoderma reesei cellobiohydrolase I w e d converted to a hybrid mammalian-type structure. Successful modification varied markedly with the strain of Z reesei used to produce cellobiohydrolase I. In vitro pretreatment of fungal glycoproteins with Aspergillus saitoi u-1,2-mannosidase improved subsequent hybrid formation. It was, however, not possible to trim all fungal oligosaccharides to an acceptor substrate for mammalian glycosyltransferases. With Z reesei RUTC 30, capping glucose residues and phosphate groups were shown to be responsible for this lack of trimming. N-glycan processing in i ? reesei apparently involves different steps, including a-12-mannosidase trimmings, and thus resembles the first mammalian glycosylation processes. The a-1,2-mannosidase trimming steps can be exploited for further in vitro a n d or in vivo synthesis of complex oligosaccharides on (heterologous) glycoproteins from filamentous fungi.
Glycobiology, 2002
Mass spectrometric techniques combined with enzymatic digestions were applied to determine the glycosylation profiles of cellobiohydrolase (CBH II) and endoglucanases (EG I, II) purified from filamentous fungus Trichoderma reesei. Electrospray mass spectrometry (ESMS) analyses of the intact cellulases revealed the microheterogeneity in glycosylation where glycoforms were spaced by hexose units. These analyses indicated that glycosylation accounted for 12-24% of the molecular mass and that microheterogeneity in both N-and O-linked glycans was observed for each glycoprotein. The identification of N-linked attachment sites was carried out by MALDI-TOF and capillary liquid chromatography-ESMS analyses of tryptic digests from each purified cellulase component with and without PNGase F incubation. Potential tryptic glycopeptide candidates were first detected by stepped orificevoltage scanning and the glycan structure and attachment site were confirmed by tandem mass spectrometry. For purified CBH II, 74% of glycans found on Asn310 were high mannose, predominantly Hex 7-9 GlcNAc 2 , whereas the remaining amount was single GlcNAc; Asn289 had 18% single GlcNAc occupancy, and Asn14 remained unoccupied. EG I presented N-linked glycans at two out of the six potential sites. The Asn56 contained a single GlcNAc residue, and Asn182 showed primarily a high-mannose glycan Hex 8 GlcNAc 2 with only 8% being occupied with a single GlcNAc. Finally, EG II presented a single GlcNAc residue at Asn103. It is noteworthy that the presence of a single GlcNAc in all cellulase enzymes investigated and the variability in site occupancy suggest the secretion of an endogenous endo H enzyme in cultures of T. reesei.
Microbiology (Reading, England), 2000
The authors have developed methodology to study the kinetics of protein synthesis and secretion in filamentous fungi. Production of cellobiohydrolase I (CBHI) by Trichoderma reesei was studied by metabolic labelling of the proteins in vivo with [35S]methionine or [14C]mannose, and subsequent analysis of the labelled proteins using two-dimensional gel electrophoresis. Analysis of the different pl forms of the nascent proteins allowed monitoring of the maturation of CBHI during the transport along the biosynthetic pathway. The maturation of the pi pattern of CBHI as well as secretion into culture medium was prevented by treatment with the reducing agent DTT. The pl forms of CBHI detectable in the presence of DTT corresponded to the early endoplasmic reticulum forms of the protein. Removal of N-glycans by enzymic treatment (endoglycosidase H or peptide-N-glycosidase F), or chemical removal of both N- and O-glycans, changed the pl pattern of CBHI, showing that glycan structures are invo...
Glycosylation of acetylxylan esterase from Trichoderma reesei
Glycobiology, 2002
The nature of the N-and O-linked glycosylation of acetylxylan esterase (AXE) of the Trichoderma reesei strain Rut-C30 has been characterized using different enzymatic, chromatographic, and mass spectrometric techniques. The combined data showed that the AXE N-glycan is phosphorylated and highly mannosylated. The predominant N-glycans on the single glycosylation site on AXE can be represented as GlcNAc 2 Man (1-6) P. The linker-substrate binding domain peptide separated from the core by papain digestion is heavily O-glycosylated and consists of mannose, galactose, and possibly glucose as monosaccharide and disaccharide substituents. In addition to glycosylation, sulfation was observed in the linker region. Both N-and O-linked glycans show remarkable heterogeneity. Three isoforms of AXE, separated by 2D SDS-PAGE, are described with pI values of 5.0, 5.3, and 5.9. The three isoforms can be explained by posttranslational modification of the enzyme by glycans, phosphate, and sulfate. Advancing the knowledge on the nature of the glycans produced by T. reesei is elementary for its use as a host for the expression of heterologous glycoproteins of industrial and pharmaceutical importance.
Using anion-exchange chromatography the catalytic domain of endoglucanase 1 (Cel7B) from Trichoderma reesei was resolved in multiple fractions with different isoelectric points, presumably related to different glyco-forms of the enzyme. The protein fractions were analysed using lectins and electrospray MS. Isolated N-glycans were analysed by fluorophore-assisted carbohydrate electrophoresis and amine-adsorption HPLC. The results show that this particular preparation contained at least 14 different glycoforms. The major isoform contained only one GlcNAc, presumably N-linked, and one mannose, most probably O-linked to serine/threonine at a separate site. Except for a small population containing Man 5 GlcNAc 2 +1–2 Man, the rest of the protein had negatively charged phosphate-containing N-glycans. All glycoforms contained at least one O-linked mannose residue. The increased negative charge of the protein, introduced by oligosaccharide phosphorylation, is the most probable reason for the different isoelectric points and the occurrence of multiple peaks during purification.
Journal of Biological Chemistry, 2019
N-Linked glycans play important roles in various cellular and immunological events. Endo--N-acetylglucosaminidase (ENGase) can release or transglycosylate N-glycans and is a promising tool for the chemoenzymatic synthesis of glycoproteins with homogeneously modified glycans. The ability of ENGases to act on core-fucosylated glycans is a key factor determining their therapeutic utility because mammalian N-glycans are frequently ␣-1,6-fucosylated. Although the biochemistries and structures of various ENGases have been studied extensively, the structural basis for the recognition of the core fucose and the asparagine-linked GlcNAc is unclear. Herein, we determined the crystal structures of a core fucosespecific ENGase from the caterpillar fungus Cordyceps militaris (Endo-CoM), which belongs to glycoside hydrolase family 18. Structures complexed with fucose-containing ligands were determined at 1.75-2.35 Å resolutions. The fucose moiety linked to GlcNAc is extensively recognized by protein residues in a round-shaped pocket, whereas the asparagine moiety linked to the GlcNAc is exposed to the solvent. The N-glycan-binding cleft of Endo-CoM is Y-shaped, and several lysine and arginine residues are present at its terminal regions. These structural features were consistent with the activity of Endo-CoM on fucose-containing glycans on rituximab (IgG) and its preference for a sialobiantennary substrate. Comparisons with other ENGases provided structural insights into their core fucose tolerance and specificity. In particular, Endo-F3, a known core fucose-specific ENGase, has a similar fucose-binding pocket, but the surrounding residues are not shared with Endo-CoM. Our study provides a foothold for protein engineering to develop enzymatic tools for the preparation of more effective therapeutic antibodies. N-Linked glycans are oligosaccharides attached to Asn residues of proteins and have key functionalities in various cellular and immunological systems (1, 2). N-Glycans are categorized into three major types, high-mannose, complex, and hybrid types, and there are bi-, tri-, and tetra-antennary glycans with respect to the number of branches (3). Mammalian N-glycans are frequently ␣-1,6-fucosylated at the Asn-linked GlcNAc of the core N,NЈ-diacetylchitobiose unit. A high-throughput analysis of the IgG glycome in three isolated human populations revealed that between 91 and 97.7% of N-glycans are core-fucosylated (4). The ␣-1,6-fucosylation plays important roles in the functionalities of epidermal growth factor receptors, cell adhesion molecules (5), and antibody-dependent cellular toxicity (6), and altered core fucosylation levels have been observed in certain types of diseases (7-9). Endo--N-acetylglucosaminidases (ENGases, 2 EC 3.2.1.96) hydrolytically cleave the -1,4-glycosidic bonds within the core N,NЈ-diacetylchitobiose unit to release N-glycan, leaving a GlcNAc, with or without the core fucose, linked to the Asn residue of proteins (Fig. 1A) (10). The ability of ENGases to chemoenzymatically synthesize homogeneously N-glycosylated proteins (antibodies) has recently attracted significant research attention (11-13). In the Carbohydrate-Active enZyme (CAZy) database (http://www.cazy.org), 3 ENGases are classified into glycoside hydrolase (GH) families 18 (GH18), GH73, and GH85 (14). ENGases in GH18 and GH85 catalyze the anomer-retaining type of hydrolysis via the "substrate-assisted" mechanism, in which the N-acetyl group of the substrate GlcNAc participates in the reaction as a nucleophile (15, 16).
O-Glycosylation of Proteins by Membrane Fractions of Trichoderma reesei QM 9414
Microbiology, 1989
In order to investigate 0-glycosylation of proteins in the fungus Trichoderma reesei QM 9414, a membrane preparation was isolated and used to study the glycosylation of endogenous proteins. Exogenously added GDP-[ U-4C]mannose was used to mannosylate both endogenous lipid and protein. The kinetics of mannosylation together with pulse-chase experiments with cold GDPmannose revealed that lipid was labelled before protein. The lipid was identified as mannosyl phosphoryl dolichol (Dol-P-Man) by TLC together with an authentic standard from yeast. Addition of tsushimycin, a specific inhibitor of Dol-P-Man synthesis, completely blocked transfer of mannose from GDP-[ U-l 4C]mannose to endogenous lipid. The mannosyl units transferred to endogenous protein could be released by p-elimination, and were shown to consist mainly of tetra-, di-and monomannosyl chains. Mannosylation of endogenous proteins occurred at a lower rate with membranes isolated from glycerol-grown cells. This could be overcome by addition of cold GDP-mannose, suggesting a limitation of endogenous GDP-mannose and/or dolichol phosphate in glycerol-grown (i.e. catabolite-repressed) cells.
European Journal of Biochemistry, 1998
Cellobiohydrolase I is an industrially important exocellulase secreted in high yields by the filamentous fungus Trichoderma reesei. The nature and effect of glycosylation of CBHI and other cellulolytic enzymes is largely unknown, although many other structural and mechanistic aspects of cellulolytic enzymes are well characterised. Using a combination of liquid chromatography, electrospray mass spectrometry, solidphase Edman degradation, and monosaccharide analysis we have identified every site of glycosylation of CBHI from a high cellulase-producing mutant strain of T. reesei, ALKO2877, and characterised each site in terms of its modifying carbohydrate and site-specific heterogeneity. The catalytic core domain comprises three N-linked glycans which each consist of a single N-acetylglucosamine residue. Within the glycopeptide linker domain, all eight threonines are variably glycosylated with between at least one, and up to three, mannose residues per site. All serines in this domain are at least partially glycosylated with a single mannose residue. This linker region has also been shown to be sulfated by a combination of ion chromatography and collision-induced dissociation electrospray mass spectrometry. The sulfate is probably mannose-linked. The biological significance of N-linked single N-acetylglucosamine in the catalytic core, and mannose sulfation in the linker region, is not known.
Glycobiology, 2004
The glycosylation of Cel7A (CBH I) from Trichoderma reesei varies considerably when the fungus is grown under different conditions. As shown by ESI-MS and PAG-IEF analyses of both intact protein and the isolated catalytic core module, the microheterogeneity originates mainly from the variable ratio of single N-acetylglucosamine over high-mannose structures on the three N-glycosylation sites and from the presence or absence of phosphate residues. Fully N-and O-glycosylated Cel7A can only be isolated from minimal medium and probably reflects the initial complexity of the protein on leaving the glycosynthetic pathway. Extracellular activities are responsible for postsecretorial modifications in other cultivation conditions: a-(132)-mannosidase, a-(133)-glucosidase and an Endo H type activity participate in N-deglycosylation (core), whereas a phosphatase and a mannosidase are probably responsible for hydrolysis of O-glycans (linker). The effects are most prominent in corn steep liquor±enriched media, where the pH is closer to the pH optimum (5±6) of these extracellular hydrolases. In minimal medium, the low pH and the presence of proteases could explain for the absence of such activities. On the other hand, phosphodiester linkages in the catalytic module are only observed under specific conditions. The extracellular trigger is still unknown, but mannophosphorylation may be regulated intracellularly by a-(132)mannosidases and phosphomannosyl transferases competing for the same intermediate in the glycosynthetic pathway.
Glycobiology, 2004
A systematic analysis of the N-glycosylation of the catalytic domain of cellobiohydrolase I (Cel7A or CBH I) isolated from several Trichoderma reesei strains grown in minimal media was performed. Using a combination of chromatographic, electrophoretic, and mass spectrometric methods, the presence of glucosylated and phosphorylated oligosaccharides on the three N-glycosylation sites of Cel7A core protein (from T. reesei strains Rut-C30 and RL-P37) confirms previous findings. With N-glycans isolated from other strains, no end-capping glucose could be detected. Phosphodiester linkages were however found in proteins from each strain and these probably occur on both the a1-3 and the a1-6 branch of the highmannose oligosaccharide tree. Evidence is also presented for the occurrence of mannobiosyl units on the phosphodiester linkage. Therefore the predominant N-glycans on Cel7A can be represented as (ManP) 0±1 GlcMan 7±8 GlcNAc 2 for the hyperproducing Rut-C30 and RL-P37 mutants and as (Man 1±2 P) 0±1±2 Man 5±6±7 GlcNAc 2 for the wild-type strain and the other mutants. As shown by ESI-MS, random substitution of these structures on the N-glycosylation sites explains the heterogeneous glycoform population of the isolated core domains. PAG-IEF separates up to five isoforms, resulting from posttranslational modification of Cel7A with mannosyl phosphodiester residues at the three distinct sites. This study clearly shows that posttranslational phosphorylation of glycoproteins is not atypical for Trichoderma sp. and that, in the case of the Rut-C30 and RL-P37 strains, the presence of an end-capped glucose residue at the a1-3 branch apparently hinders a second mannophoshoryl transfer.
Malaysian Journal of Microbiology, 2006
Chitinase 42 kDa produced by Trichoderma harzianum has been proven as a prime compound to be excreted onto the hyphae of the pathogen causing localised cell wall lysis at the point of interaction. This finally initiate the process of the host cell becomes empty of cytoplasm, disintegrates and shows a rapid collapse. This study investigates the existence of N-glycan linked mannose in chitinase 42 kDa produced by the Malaysian T. harzianum strain BIO10671. The chitinase 42 kDa from T. harzianum BIO10671 was initially purified using anion exchange chromatography prior to a series of experiments such as immunoblotting against the chitinase 42 kDa antibody, lectin staining for detecting any terminal linked mannose, andgalactofuranose detection to determine the presence of galatofuranose components in glycoproteins. The enzyme purification harvested about 12-fold of chitinase 42 kDa from T. harzianum BIO10671 with strong indication of the presence chitinase 42 kDa presence on SDS-Page. This was confirmed by immunoblotting with a strong response around 42 kDa after overnight incubation in chitinase 42 kDa antibody suggesting that the gene for chitinase 42 kDa was greatly expressed in this strain. There are no intervation of galatofuranose on any of the terminal mannose in chitinase 42 kDa as shown by negative results on samples treated with or without endoglycosidase-H and lectin staining. Therefore, it can be concludeed that glycosylation occurred in the chitinase 42 kDa from T. harzianum 42 kDa was not in the form of N-glycan linked mannose as expected.
Current Research Topics in Applied Microbiology and Microbial Biotechnology, 2009
Botryosphaeran, a new exopolysaccharide from the endophytic fungus Botryosphaeria rhodina MAMB-05, and algal laminarin were hydrolyzed by partially-fractionated enzymes of the β-glucanolytic complex from Trichoderma harzianum Rifai. β-Glucanase fractions (F-I and F-II) separated by gel permeation chromatography presented different modes of attack on botryosphaeran and laminarin. Botryosphaeran was hydrolyzed to the extent of 66% (F-I) and 98% (F-II) within 30 min, and its main hydrolysis products were gluco-oligosaccharides of DP≥4, with lesser amounts of glucose, di-and tri-saccharides. The action of enzyme fractions I and II on laminarin resulted in 15% conversion to glucose, while the percentage of saccharification was radically different (70% for F-I and 25% for F-II). The different product arrays within the polysaccharide hydrolysates can be explained by the difference in the enzymes' specificities within each enzyme fraction, and the molecular structures of the polysaccharides and their complexity.
Glycobiology, 2006
In this study, we show that introduction of human N-acetylglucosaminyltransferase (GnT)-III gene into tobacco plants leads to highly efficient synthesis of bisected N-glycans. Enzymatically released N-glycans from leaf glycoproteins of wild-type and transgenic GnT-III plants were profiled by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) in native form. After labeling with 2-aminobenzamide, profiling was performed using normal-phase high-performance liquid chromatography with fluorescence detection, and glycans were structurally characterized by MALDI-TOF/TOF-MS and reversephase nano-liquid chromatography-MS/MS. These analyses revealed that most of the complex-type N-glycans in the plants expressing GnT-III were bisected and carried at least two terminal N-acetylglucosamine (GlcNAc) residues in contrast to wild-type plants, where a considerable proportion of N-glycans did not contain GlcNAc residues at the nonreducing end. Moreover, we have shown that the majority of N-glycans of an antibody produced in a plant expressing GnT-III is also bisected. This might improve the efficacy of therapeutic antibodies produced in this type of transgenic plant.
FEBS Letters, 2001
Therapeutic glycoprotein production in the widely used expression host Pichia pastoris is hampered by the differences in the protein-linked carbohydrate biosynthesis between this yeast and the target organisms such as man. A significant step towards the generation of human-compatible N-glycans in this organism is the conversion of the yeast-type high-mannose glycans to mammalian-type high-mannose and/or complex glycans. In this perspective, we have co-expressed an endoplasmic reticulum-targeted Trichoderma reesei 1,2-K K-Dmannosidase with two glycoproteins: influenza virus haemagglutinin and Trypanosoma cruzi trans-sialidase. Analysis of the N-glycans of the two purified proteins showed a s 85% decrease in the number of K K-1,2-linked mannose residues. Moreover, the human-type high-mannose oligosaccharide Man 5 GlcNAc 2 was the major N-glycan of the glyco-engineered trans-sialidase, indicating that N-glycan engineering can be effectively accomplished in P. pastoris.
Production of Complex Multiantennary N-Glycans in Nicotiana benthamiana Plants
PLANT PHYSIOLOGY, 2011
In recent years, plants have been developed as an alternative expression system to mammalian hosts for the production of therapeutic proteins. Many modifications to the plant glycosylation machinery have been made to render it more human because of the importance of glycosylation for functionality, serum half-life, and the safety profile of the expressed proteins. These modifications include removal of plant-specific b1,2-xylose and core a1,3-fucose, and addition of bisecting N-acetylglucosamine, b1,4-galactoses, and sialic acid residues. Another glycosylation step that is essential for the production of complex human-type glycans is the synthesis of multiantennary structures, which are frequently found on human N-glycans but are not generated by wild-type plants. Here, we report both the magnICON-based transient as well as stable introduction of the a1,3-mannosyl-b1,4-N-acetylglucosaminyltransferase (GnT-IV isozymes a and b) and a1,6-mannosyl-b1,6-N-acetylglucosaminyltransferase (GnT-V) in Nicotiana benthamiana plants. The enzymes were targeted to the Golgi apparatus by fusing their catalytic domains to the plant-specific localization signals of xylosyltransferase and fucosyltransferase. The GnT-IV and-V modifications were tested in the wild-type background, but were also combined with the RNA interference-mediated knockdown of b1,2-xylosyltransferase and a1,3-fucosyltransferase. Results showed that triantennary Gn[GnGn] and [GnGn]Gn N-glycans could be produced according to the expected activities of the respective enzymes. Combination of the two enzymes by crossing stably transformed GnT-IV and GnT-V plants showed that up to 10% tetraantennary [GnGn][GnGn], 25% triantennary, and 35% biantennary N-glycans were synthesized. All transgenic plants were viable and showed no aberrant phenotype under standard growth conditions.
Applied and Environmental Microbiology, 2005
We describe isolation and characterization of the gene encoding the glucosidase II alpha subunit (GII␣) of the industrially important fungus Trichoderma reesei. This subunit is the catalytic part of the glucosidase II heterodimeric enzyme involved in the structural modification within the endoplasmic reticulum (ER) of N-linked oligosaccharides present on glycoproteins. The gene encoding GII␣ (gls2␣) in the hypercellulolytic strain Rut-C30 contains a frameshift mutation resulting in a truncated gene product. Based on the peculiar monoglucosylated N-glycan pattern on proteins produced by the strain, we concluded that the truncated protein can still hydrolyze the first ␣-1,3-linked glucose residue but not the innermost ␣-1,3-linked glucose residue from the Glc 2 Man 9 GlcNAc 2 N-glycan ER structure. Transformation of the Rut-C30 strain with a repaired T. reesei gls2␣ gene changed the glycosylation profile significantly, decreasing the amount of monoglucosylated structures and increasing the amount of high-mannose N-glycans. Full conversion to highmannose carbohydrates was not obtained, and this was probably due to competition between the endogenous mutant subunit and the introduced wild-type GII␣ protein. Since glucosidase II is also involved in the ER quality control of nascent polypeptide chains, its transcriptional regulation was studied in a strain producing recombinant tissue plasminogen activator (tPA) and in cultures treated with the stress agents dithiothreitol (DTT) and brefeldin A (BFA), which are known to block protein transport and to induce the unfolded protein response. While the mRNA levels were clearly upregulated upon tPA production or BFA treatment, no such enhancement was observed after DTT addition.
Gene, 2001
A gene (gluc78) encoding an antifungal glucan 1,3-b-glucosidase was cloned from strain P1 of the biocontrol fungus Trichoderma atroviride (formerly T. harzianum). A putative regulatory sequence upstream from the coding region was cloned using single-strand extension from a primer in the known portion of the gene, circularized with T4 ligase, and then reamplified with PCR to generate double-stranded DNA. The entire genomic DNA sequence consisted of 3440 bp, with 559 and 579 bp, respectively, in 5 0 and 3 0 untranslated regions. The transcription unit contains a single intron, positioned in the 5 0 untranslated region. The gene encodes for a protein of 770 aa, including a 40 aa signal peptide. Symmetry between the first and second halves of the mature protein was found. The gene is present as a single copy in T. atroviride and a similar gene also is present in T. harzianum and T. virens. The encoded protein has similarity to a small group of sequences from filamentous fungi and no significant similarity to 1,3-b-glucanases or glucosidases from other organisms. Northern analysis indicates that the gene is repressed in the presence of 3% glucose and expressed in media containing 0.1% of the sugar. Laminarin (0.1%) enhances expression after 18 h and other polymers such as scleroglucan and pustulan may enhance expression after 40 h of growth.
Journal of Biological Chemistry, 2011
N-Glycosylation, a major co-and post-translational event in the synthesis of proteins in eukaryotes, is unknown in aquatic photosynthetic microalgae. In this paper, we describe the Nglycosylation pathway in the diatom Phaeodactylum tricornutum. Bio-informatic analysis of its genome revealed the presence of a complete set of sequences potentially encoding for proteins involved in the synthesis of the lipid-linked Glc 3 Man 9 GlcNAc 2 -PP-dolichol N-glycan, some subunits of the oligosaccharyltransferase complex, as well as endoplasmic reticulum glucosidases and chaperones required for protein quality control and, finally, the ␣-mannosidase I involved in the trimming of the N-glycan precursor into Man-5 N-glycan. Moreover, one N-acetylglucosaminyltransferase I, a Golgi glycosyltransferase that initiates the synthesis of complex type N-glycans, was predicted in the P. tricornutum genome. We demonstrated that this gene encodes for an active N-acetylglucosaminyltransferase I, which is able to restore complex type N-glycans maturation in the Chinese hamster ovary Lec1 mutant, defective in its endogeneous N-acetylglucosaminyltransferase I. Consistent with these data, the structural analyses of N-linked glycans demonstrated that P. tricornutum proteins carry mainly high mannose type N-glycans ranging from Man-5 to Man-9. Although representing a minor glycan population, paucimannose N-glycans were also detected, suggesting the occurrence of an N-acetylglucosaminyltransferase I-dependent maturation of N-glycans in this diatom. and M. B.). 1 Fellow of the French Ministry for Research and Higher Education. 2 Present address: Algenics S. A. S., Pô le Bio Ouest, Rue du Moulin de la Rousseliè re,