Molecular cloning and characterization of a novel alpha 1,2-fucosyltransferase (CE2FT-1) from Caenorhabditis elegans

Cloning, expression and characterisation of a novel mollusc α-1,2-Fucosyltransferase from Crassostrea gigas (CgFUT2)

Glycans containing fucose play crucial roles in cell biology, particularly in recognition processes. In humans, fucose found in H-blood group antigens is recognized by various pathogens, thereby influencing host-pathogen interactions. However, in invertebrate biology the specific functions of these modifications and the corresponding glycosyltransferases are not fully elucidated. Therefore, cloning these glycosyltransferases from different model systems will provide valuable insights into this process. Little is known about fucosyltransferases in molluscs. For this study, a sequence of the Pacific oyster, Crassostrea gigas, based on amino acid sequence homologies with rabbit and human α-1,2-fucosyltransferases, was chosen. The recombinant enzyme (350 amino acids) was able to transfer fucose from GDP-fucose to the galactose residue of type II disaccharides, terminal galactoses in complex N-glycan structures and several linear and branched galactans which were tested using a glycan microarray. The α-1,2-linkage formed was confirmed by NMR analysis. The enzyme was active in a broad pH-range, it was relatively stable upon storage conditions and its activity was not dependent on the presence of divalent cations. In this study, we were able to clone, express and characterise a novel α-1,2-fucosyltrasferase from Crassostrea gigas (CgFUT2).

Structural insights into the fungi-nematodes interaction mediated by fucose-specific lectin AofleA from Arthrobotrys oligospora

Fungal lectin can bind specific carbohydrate structures of the host and work in recognition and adhesion or as a toxic factor. AofleA, as a fucose-specific lectin from widely studied nematode predatory fungus Arthrobotrys oligospora, possibly plays a key role in the event of capturing nematodes, but the mechanism remains unknown. Here we report the crystal structure of AofleA, which exists as a homodimer with each subunit folds as a six-bladed β-propeller. Our structural and biological results revealed that three of the six putative binding sites of AofleA had fucose-binding abilities. In addition, we found that AofleA could bind to the pharynx and intestine of the nematode in a fucose-binding-dependent manner. Our results facilitate the understanding of the mechanism that fucose-specific lectin mediates fungi-nematodes interaction, and provide structural information for the development of potential applications of AofleA.

N-glycomic Complexity in Anatomical Simplicity: Caenorhabditis elegans as a Non-model Nematode?

Caenorhabditis elegans is a genetically well-studied model nematode or "worm"; however, its N-glycomic complexity is actually baffling and still not completely unraveled. Some features of its N-glycans are, to date, unique and include bisecting galactose and up to five fucose residues associated with the asparagine-linked Man2-3GlcNAc2 core; the substitutions include galactosylation of fucose, fucosylation of galactose and methylation of mannose or fucose residues as well as phosphorylcholine on antennal (non-reducing) N-acetylglucosamine. Only some of these modifications are shared with various other nematodes, while others have yet to be detected in any other species. Thus, C. elegans can be used as a model for some aspects of N-glycan function, but its glycome is far from identical to those of other organisms and is actually far from simple. Possibly the challenges of its native environment, which differ from those of parasitic or necromenic species, led to an anatomically simple worm possessing a complex glycome.

Core Richness of N-Glycans of Caenorhabditis elegans: A Case Study on Chemical and Enzymatic Release

Despite years of research, the glycome of the model nematode Caenorhabditis elegans is still not fully understood. Certainly, data over the years have indicated that this organism synthesizes unusual N-glycans with a range of galactose and fucose modifications on the Man_2-3GlcNAc₂ core region. Previously, up to four fucose residues were detected on its N-glycans, despite these lacking the fucosylated antennae typical of many other eukaryotes; some of these fucose residues are capped with hexose residues as shown by the studies of us and others. There have, though, been contrasting reports regarding the maximal number of fucose substitutions in C. elegans, which in part may be due to different methodological approaches, including use of either peptide:N-glycosidases F and A (PNGase F and A) or anhydrous hydrazine to cleave the N-glycans from glycopeptides. Here we compare the use of hydrazine with that of a new enzyme (rice PNGase Ar) and show that both enable release of glycans with more sugar residues on the proximal GlcNAc than previously resolved. By use of exoglycosidase sequencing, in conjunction with high-performance liquid chromatography (HPLC) and matrix-assisted laser desorption ionization time-of-flight tandem mass spectrometry (MALDI-TOF MS/MS), we now reveal that actually up to five fucose residues modify the core region of C. elegans N-glycans and that the α1,3-fucose on the reducing terminus can be substituted by an α-linked galactose. Thus, traditional PNGase F and A release may be insufficient for release of the more highly core-modified N-glycans, especially those occurring in C. elegans, but novel enzymes can compete against chemical methods in terms of safety, ease of cleanup, and quality of resulting glycomic data.

The conserved oligomeric Golgi complex is required for fucosylation of N-glycans in Caenorhabditis elegans

The conserved oligomeric Golgi complex (COG) is a hetero-octomeric peripheral membrane protein required for retrograde vesicular transport and glycoconjugate biosynthesis within the Golgi. Mutations in subunits 1, 4, 5, 6, 7 and 8 are the basis for a rare inheritable human disease termed congenital disorders of glycosylation type-II. Defects to COG complex function result in aberrant glycosylation, protein trafficking and Golgi structure. The cellular function of the COG complex and its role in protein glycosylation are not completely understood. In this study, we report the first detailed structural analysis of N-glycans from a COG complex-deficient organism. We employed sequential ion trap mass spectrometry of permethylated N-glycans to demonstrate that the COG complex is essential for the formation of fucose-rich N-glycans, specifically antennae fucosylated structures in Caenorhabditis elegans. Our results support the supposition that disruption to the COG complex interferes with normal protein glycosylation in the medial and/or trans-Golgi.

Phylogenetic conservation of the cell-type-specific Lan3-2 glycoepitope in Caenorhabditis elegans

The biological function of a cell-type-specific glycosylation of an adhesion molecule belonging to the L1CAM immunoglobulin superfamily was previously determined in the nervous system of the embryonic leech, Hirudo medicinalis. The Lan3-2 glycoepitope is a surface marker of sensory afferent neurons and is required for their appropriate developmental collateral branching and synaptogenesis in the CNS. The chemical structure of the Lan3-2 glycoepitope consists of beta-(1,4)-linked mannopyranose. Here, we show the conservation of the cell-type-specific expression of this mannose polymer in Caenorhabditis elegans. The Lan3-2 glycoepitope is expressed on the cell surface of a subset of dissociated embryonic neurons and, in the adult worm, by the pharyngeal motor neuron, M5, and the chemosensory afferents, the amphids. Additionally, the vulval epithelium expresses the Lan3-2 glycoepitope in late L4 larvae and in adult hermaphrodites. To investigate proteins carrying this restrictively expressed glycoepitope, worm extract was immunoaffinity purified with Lan3-2 monoclonal antibody and Western blotted. A polyclonal antibody reactive with the cytoplasmic tail of LAD-1/SAX-7, a C. elegans member of the L1CAM family, recognizes a 270 kDa protein band while Lan3-2 antibody also recognizes a 190 kDa glycoform, its putative Lan3-2 ectodomain. Thus, in C. elegans, as in leech, the Lan3-2 epitope is located on a L1CAM homologue. The cell-type-specific expression of the Lan3-2 glycoepitope shared by leech and C. elegans will be useful for understanding how cell-type-specific glycoepitopes mediate cell-cell interactions during development.

Chemoenzymatic synthesis of multivalent neoglycoconjugates carrying the helminth glycan antigen LDNF

Several parasitic helminthes, such as the human parasite Schistosoma mansoni, express glycoconjugates that contain terminal GalNAc beta1-4(Fuc alpha1-3)GlcNAc beta-R (LDNF) moieties. These LDNF glycans are dominant antigens of the parasite and are recognized by human dendritic cells via the C-type lectin DC-SIGN. To study the functional role of the LDNF antigen in interaction with the immune system, we have developed an easy chemoenzymatic method to synthesize multivalent neoglycoconjugates carrying defined amounts of LDNF antigens. An acceptor substrate providing a terminal N-acetylglucosamine was prepared by coupling a fluorescent hydrophobic aglycon, 2,6-diaminopyridine (DAP), to N,N'-diacetylchitobiose. By the subsequent action of recombinant Caenorhabditis elegans beta1,4-N-acetylgalactosaminyltransferase and human alpha1,3-fucosyltransferase VI (FucT-VI), this substrate was converted to the LDNF antigen. We showed that human FucT-VI has a relatively high affinity for the unusual substrate GalNAc beta1-4GlcNAc (LDN), and this enzyme was used to produce micromolar amounts of LDNF-DAP. The synthesized LDNF-DAP was coupled to carrier protein via activation of the DAP moiety by diethyl squarate. By varying the molar glycan:protein ratio, neoglycoconjugates were constructed with defined amounts of LDNF, as was determined by MALDI-TOF analysis and ELISA using an anti-LDNF antibody.

Molecular cloning and characterization of the Caenorhabditis elegans alpha1,3-fucosyltransferase family

The genome of Caenorhabditis elegans encodes five genes with homology to known alpha1,3 fucosyltransferases (alpha1,3FTs), but their expression and functions are poorly understood. Here we report the molecular cloning and characterization of these C. elegans alpha1,3FTs (CEFT-1 through -5). The open-reading frame for each enzyme predicts a type II transmembrane protein and multiple potential N-glycosylation sites. We prepared recombinant epitope-tagged forms of each CEFT and found that they had unusual acceptor specificity, cation requirements, and temperature sensitivity. CEFT-1 acted on the N-glycan pentasaccharide core acceptor to generate Manalpha1-3(Manalpha1-6)Manbeta1-4GlcNAcbeta1-4(Fucalpha1-3)GlcNAcbeta1-Asn. In contrast, CEFT-2 did not act on the pentasaccharide acceptor, but instead utilized a LacdiNAc acceptor to generate GalNAcbeta1-4(Fucalpha1-3)GlcNAcbeta1-3Galbeta1-4Glc, which is a novel activity. CEFT-3 utilized a LacNAc acceptor to generate Galbeta1-4(Fucalpha1-3)GlcNAcbeta1-3Galbeta1-4Glc without requiring cations. CEFT-4 was similar to CEFT-3, but its activity was enhanced by some divalent cations. Recombinant CEFT-5 was well expressed, but did not act on available acceptors. Each CEFT was optimally active at room temperature and rapidly lost activity at 37 degrees C. Promoter analysis showed that CEFT-1 is expressed in C. elegans eggs and adults, but its expression was restricted to a few neuronal cells at the head and tail. We prepared deletion mutants for each enzyme for phenotypic analysis. While loss of CEFT-1 correlated with loss of pentasaccharide core activity and core alpha1,3-fucosylated glycans in worms, loss of other enzymes did not correlate with any phenotypic changes. These results suggest that each of the alpha1,3FTs in C. elegans has unique specificity and expression patterns.

Fucosylation in prokaryotes and eukaryotes

Fucosylated carbohydrate structures are involved in a variety of biological and pathological processes in eukaryotic organisms including tissue development, angiogenesis, fertilization, cell adhesion, inflammation, and tumor metastasis. In contrast, fucosylation appears less common in prokaryotic organisms and has been suggested to be involved in molecular mimicry, adhesion, colonization, and modulating the host immune response. Fucosyltransferases (FucTs), present in both eukaryotic and prokaryotic organisms, are the enzymes responsible for the catalysis of fucose transfer from donor guanosine-diphosphate fucose to various acceptor molecules including oligosaccharides, glycoproteins, and glycolipids. To date, several subfamilies of mammalian FucTs have been well characterized; these enzymes are therefore delineated and used as models. Non-mammalian FucTs that possess different domain construction or display distinctive acceptor substrate specificity are highlighted. It is noteworthy that the glycoconjugates from plants and schistosomes contain some unusual fucose linkages, suggesting the presence of novel FucT subfamilies as yet to be characterized. Despite the very low sequence homology, striking functional similarity is exhibited between mammalian and Helicobacter pylori alpha1,3/4 FucTs, implying that these enzymes likely share a conserved mechanistic and structural basis for fucose transfer; such conserved functional features might also exist when comparing other FucT subfamilies from different origins. Fucosyltranferases are promising tools used in synthesis of fucosylated oligosaccharides and glycoconjugates, which show great potential in the treatment of infectious and inflammatory diseases and tumor metastasis.

Identification of core 1 O-glycan T-synthase from Caenorhabditis elegans

The common O-glycan core structure in animal glycoproteins is the core 1 disaccharide Galbeta1-3GalNAcalpha1-Ser/Thr, which is generated by the addition of Gal to GalNAcalpha1-Ser/Thr by core 1 UDP-alpha-galactose (UDP-Gal):GalNAcalpha1-Ser/Thr beta1,3-galactosyltransferase (core 1 beta3-Gal-T or T-synthase, EC2.4.1.122). Although O-glycans play important roles in vertebrates, much remains to be learned from model organisms such as the free-living nematode Caenorhabditis elegans, which offer many advantages in exploring O-glycan structure/function. Here, we report the cloning and enzymatic characterization of T-synthase from C. elegans (Ce-T-synthase). A putative C. elegans gene for T-synthase, C38H2.2, was identified in GenBank by a BlastP search using the human T-synthase protein sequence. The full-length cDNA for Ce-T-synthase, which was generated by polymerase chain reaction using a C. elegans cDNA library as the template, contains 1170 bp including the stop TAA. The cDNA encodes a protein of 389 amino acids with typical type II membrane topology and a remarkable 42.7% identity to the human T-synthase. Ce-T-synthase has seven Cys residues in the lumenal domain including six conserved Cys residues in all orthologs. The Ce-T-synthase has four potential N-glycosylation sequons, whereas the mammalian orthologs lack N-glycosylation sequons. Only one gene for Ce-T-synthase was identified in the genome-wide search, and it contains eight exons. Promoter analysis of the Ce-T-synthase using green fluorescent protein (GFP) constructs shows that the gene is expressed at all developmental stages and appears to be in all cells. Unexpectedly, only minimal activity was recovered in the recombinant, soluble Ce-T-synthase secreted from a wide variety of mammalian cell lines, whereas robust enzyme activity was recovered in the soluble Ce-T-synthase expressed in Hi-5 insect cells. Vertebrate T-synthase requires the molecular chaperone Cosmc, but our results show that Ce-T-synthase does not require Cosmc and might require invertebrate-specific factors for the formation of the optimally active enzyme. These results show that the Ce-T-synthase is a functional ortholog to the human T-synthase in generating core 1 O-glycans and open new avenues to explore O-glycan function in this model organism.

Construction of a human glycogene library and comprehensive functional analysis

Eighteen years have passed after the first mammalian glycosyltransferase was cloned. At the beginning of April, 2001, 110 genes for human glycosyltransferases, including modifying enzymes for carbohydrate chains such as sulfotransferases, had been cloned and analyzed. We started the Glycogene Project (GG project) in April 2001, a comprehensive study on human glycogenes with the aid of bioinformatic technology. The term glycogene includes the genes for glycosyltransferases, sulfotransferases adding sulfate to carbohydrates and sugar-nucleotide transporters, etc. Firstly, as many novel genes, which are the candidates for glycogenes, as possible were searched using bioinformatic technology in databases. They were then cloned and expressed in various expression systems to detect the activity for carbohydrate synthesis. Their substrate specificity was determined using various acceptors.

Protein glycosylation lessons from Caenorhabditis elegans

From observations on human diseases and mutant mice, it has become clear that glycosylation plays a major role in metazoan development. Caenorhabditis elegans provides powerful tools to study this problem that are not available in men or mice. The worm has many genes homologous to mammalian genes involved in glycosylation. Glycobiologists have, in recent years, cloned and expressed some of these genes and studied the effects of mutations on worm development. Recent studies have focused on N-glycosylation, lumenal nucleoside diphosphatases, the resistance of C. elegans to a bacterial toxin and infections, fucosylation and proteoglycans.

Fucosyltransferase substrate specificity and the order of fucosylation in invertebrates

Core alpha1,6-fucosylation is a conserved feature of animal N-linked oligosaccharides being present in both invertebrates and vertebrates. To prove that the enzymatic basis for this modification is also evolutionarily conserved, cDNAs encoding the catalytic regions of the predicted Caenorhabditis elegans and Drosophila melanogaster homologs of vertebrate alpha1,6-fucosyltransferases (E.C. 2.4.1.68) were engineered for expression in the yeast Pichia pastoris. Recombinant forms of both enzymes were found to display core fucosyltransferase activity as shown by a variety of methods. Unsubstituted nonreducing terminal GlcNAc residues appeared to be an obligatory feature of the substrate for the recombinant Caenorhabditis and Drosophila alpha1,6-fucosyltransferases, as well as for native Caenorhabditis and Schistosoma mansoni core alpha1,6-fucosyltransferases. On the other hand, these alpha1,6-fucosyltransferases could not act on N-glycopeptides already carrying core alpha1,3-fucose residues, whereas recombinant Drosophila and native Schistosoma core alpha1,3-fucosyltransferases were able to use core alpha1,6-fucosylated glycans as substrates. Lewis-type fucosylation was observed with native Schistosoma extracts and could take place after core alpha1,3-fucosylation, whereas prior Lewis-type fucosylation precluded the action of the Schistosoma core alpha1,3-fucosyltransferase. Overall, we conclude that the strict order of fucosylation events, previously determined for fucosyltransferases in crude extracts from insect cell lines (core alpha1,6 before core alpha1,3), also applies for recombinant Drosophila core alpha1,3- and alpha1,6-fucosyltransferases as well as for core fucosyltransferases in schistosomal egg extracts.

Molecular Basis of Anti-horseradish Peroxidase Staining in Caenorhabditis elegans

Cross-reactivity with anti-horseradish peroxidase antiserum is a feature of many glycoproteins from plants and invertebrates; indeed staining with this reagent has been used to track neurons in Drosophila melanogaster and Caenorhabditis elegans. Although in insects the evidence indicates that the cross-reaction results from the presence of core alpha1,3-fucosylated N-glycans, the molecular basis for anti-horseradish peroxidase staining in nematodes has been unresolved to date. By using Western blots of wild-type and mutant C. elegans extracts in conjunction with specific inhibitors, we show that the cross-reaction is due to core alpha1,3-fucosylation. Of the various mutants examined, one with a deletion of the fut-1 (K08F8.3) gene showed no reaction to anti-horseradish peroxidase; the molecular phenotype was rescued by injection of either the K08F8 cosmid or the fut-1 open reading frame under control of the let-858 promoter. Furthermore, expression of fut-1 cDNA in Pichia and insect cells in conjunction with antibody staining, high pressure liquid chromatography, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry analyses showed that FUT-1 is a core alpha1,3-fucosyltransferase with an unusual substrate specificity. It is the only core fucosyltransferase in plants and animals described to date that does not require the prior action of N-acetylglucosaminyltransferase I.

Role of glycosylation in development

Researchers have long predicted that complex carbohydrates on cell surfaces would play important roles in developmental processes because of the observation that specific carbohydrate structures appear in specific spatial and temporal patterns throughout development. The astounding number and complexity of carbohydrate structures on cell surfaces added support to the concept that glycoconjugates would function in cellular communication during development. Although the structural complexity inherent in glycoconjugates has slowed advances in our understanding of their functions, the complete sequencing of the genomes of organisms classically used in developmental studies (e.g., mice, Drosophila melanogaster, and Caenorhabditis elegans) has led to demonstration of essential functions for a number of glycoconjugates in developmental processes. Here we present a review of recent studies analyzing function of a variety of glycoconjugates (O-fucose, O-mannose, N-glycans, mucin-type O-glycans, proteoglycans, glycosphingolipids), focusing on lessons learned from human disease and genetic studies in mice, D. melanogaster, and C. elegans.

ire-1-dependent Transcriptional Up-regulation of a Lumenal Uridine Diphosphatase from Caenorhabditis elegans

Lumenal ecto-nucleoside tri- and di-phosphohydrolases (ENTPDases) of the secretory pathway of eukaryotes hydrolyze nucleoside diphosphates resulting from glycosyltransferase-mediated reactions, yielding nucleoside monophosphates. The latter are weaker inhibitors of glycosyltransferases than the former and are also antiporters for the transport of nucleotide sugars from the cytosol to the endoplasmic reticulum (ER) and Golgi apparatus (GA) lumen. Here we describe the presence of two cation-dependent nucleotide phosphohydrolase activities in membranes of Caenorhabditis elegans: one, UDA-1, is a UDP/GDPase encoded by the gene uda-1, whereas the other is an apyrase encoded by the gene ntp-1. UDA-1 shares significant amino acid sequence similarity to yeast GA Gda1p and mammalian UDP/GDPases and has a lumenal active site in vesicles displaying an intermediate density between those of the ER and GA when expressed in S. cerevisiae. NTP-1 expressed in COS-7 cells appeared to localize to the GA. The transcript of uda-1 but not those of two other C. elegans ENTPDase mRNAs (ntp-1 and mig-23) was induced up to 3.5-fold by high temperature, tunicamycin, and ethanol. The same effectors triggered the unfolded protein response as shown by the induction of expression of green fluorescent protein under the control of the BiP chaperone promoter and the UDP-glucose:glycoprotein glucosyltransferase. Up-regulation of uda-1 did not occur in ire-1-deficient mutants, demonstrating the role of this ER stress sensor in this event. We hypothesize that up-regulation of uda-1 favors hydrolysis of the glucosyltransferase inhibitory product UDP to UMP, and that the latter product then exits the lumen of the ER or pre-GA compartment in a coupled exchange with the entry of UDP-glucose, thereby further relieving ER stress by favoring protein re-glycosylation.