Characterization of a UDP-Gal:Galbeta1-3GalNAc alpha1, 4-galactosyltransferase activity in a Mamestra brassicae cell line

A database of crop pest cell lines

We have developed an online database describing the known cell lines from Coleoptera, Diptera, Hemiptera, Hymenoptera, and Lepidoptera that were developed from agricultural pests. Cell line information has been primarily obtained from previous compilations of insect cell lines. We conducted in-depth Internet literature searches and drew on Internet sources such as the Cellosaurus database (https://web.expasy.org/cellosaurus/), and inventories from cell line depositories. Here, we report on a new database of insect cell lines, which covers 719 cell lines from 86 species. We have not included cell lines developed from Drosophila because they are already known from published databases, such as https://dgrc.bio.indiana.edu/cells/Catalog. We provide the designation, tissue and species of origin, cell line developer, unique characteristics, its use in various applications, publications, and patents, and, when known, insect virus susceptibility. This information has been assembled and organized into a searchable database available at the link https://entomology.ca.uky.edu/aginsectcellsdatabase which will be updated on an ongoing basis.

Mucin-Type O-Glycosylation in Invertebrates

O-Glycosylation is one of the most important posttranslational modifications of proteins. It takes part in protein conformation, protein sorting, developmental processes and the modulation of enzymatic activities. In vertebrates, the basics of the biosynthetic pathway of O-glycans are already well understood. However, the regulation of the processes and the molecular aspects of defects, especially in correlation with cancer or developmental abnormalities, are still under investigation. The knowledge of the correlating invertebrate systems and evolutionary aspects of these highly conserved biosynthetic events may help improve the understanding of the regulatory factors of this pathway. Invertebrates display a broad spectrum of glycosylation varieties, providing an enormous potential for glycan modifications which may be used for the design of new pharmaceutically active substances. Here, overviews of the present knowledge of invertebrate mucin-type O-glycan structures and the currently identified enzymes responsible for the biosynthesis of these oligosaccharides are presented, and the few data dealing with functional aspects of O-glycans are summarised.

Targeted release and fractionation reveal glucuronylated and sulphated N- and O-glycans in larvae of dipteran insects

Mosquitoes are important vectors of parasitic and viral diseases with Anopheles gambiae transmitting malaria and Aedes aegypti spreading yellow and Dengue fevers. Using two different approaches (solid-phase extraction and reversed-phase or hydrophilic interaction HPLC fractionation followed by MALDI-TOF MS or permethylation followed by NSI-MS), we examined the N-glycans of both A. gambiae and A. aegypti larvae and demonstrate the presence of a range of paucimannosidic glycans as well as bi- and tri-antennary glycans, some of which are modified with fucose or with sulphate or glucuronic acid residues; the latter anionic modifications were also found on N-glycans of larvae from another dipteran species (Drosophila melanogaster). The sulphate groups are attached primarily to core α-mannose residues (especially the α1,6-linked mannose), whereas the glucuronic acid residues are linked to non-reducing β1,3-galactose. Also, O-glycans were found to possess glucuronic acid and sulphate as well as phosphoethanolamine modifications. The presence of sulphated and glucuronylated N-glycans is a novel feature in dipteran glycomes; these structures have the potential to act as additional anionic glycan ligands involved in parasite interactions with the vector host.

Specificity analysis of lectins and antibodies using remodeled glycoproteins

Due to their ability to bind specifically to certain carbohydrate sequences, lectins are a frequently used tool in cytology, histology, and glycan analysis but also offer new options for drug targeting and drug delivery systems. For these and other potential applications, it is necessary to be certain as to the carbohydrate structures interacting with the lectin. Therefore, we used glycoproteins remodeled with glycosyltransferases and glycosidases for testing specificities of lectins from Aleuria aurantia (AAL), Erythrina cristagalli (ECL), Griffonia simplicifolia (GSL I-B(4)), Helix pomatia agglutinin (HPA), Lens culinaris (LCA), Lotus tetragonolobus (LTA), peanut (Arachis hypogaeae) (PNA), Ricinus communis (RCA I), Sambucus nigra (SNA), Vicia villosa (VVA), and wheat germ (Triticum vulgaris) (WGA) as well as reactivities of anti-carbohydrate antibodies (anti-bee venom, anti-horseradish peroxidase [anti-HRP], and anti-Lewis(x)). After enzymatic remodeling, the resulting neoglycoforms display defined carbohydrate sequences and can be used, when spotted on nitrocellulose or in enzyme-linked lectinosorbent assays, to identify the sugar moieties bound by the lectins. Transferrin with its two biantennary complex N-glycans was used as scaffold for gaining diverse N-glycosidic structures, whereas fetuin was modified using glycosidases to test the specificities of lectins toward both N- and O-glycans. In addition, alpha(1)-acid glycoprotein and Schistosoma mansoni egg extract were chosen as controls for lectin interactions with fucosylated glycans (Lewis(x) and core alpha1,3-fucose). Our data complement and expand the existing knowledge about the binding specificity of a range of commercially available lectins.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update covering the period 1999-2000

This review describes the use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the analysis of carbohydrates and glycoconjugates and continues coverage of the field from the previous review published in 1999 (D. J. Harvey, Matrix-assisted laser desorption/ionization mass spectrometry of carbohydrates, 1999, Mass Spectrom Rev, 18:349-451) for the period 1999-2000. As MALDI mass spectrometry is acquiring the status of a mature technique in this field, there has been a greater emphasis on applications rather than to method development as opposed to the previous review. The present review covers applications to plant-derived carbohydrates, N- and O-linked glycans from glycoproteins, glycated proteins, mucins, glycosaminoglycans, bacterial glycolipids, glycosphingolipids, glycoglycerolipids and related compounds, and glycosides. Applications of MALDI mass spectrometry to the study of enzymes acting on carbohydrates (glycosyltransferases and glycosidases) and to the synthesis of carbohydrates, are also covered.

The Drosophila melanogaster homologue of the human histo-blood group Pk gene encodes a glycolipid-modifying alpha1,4-N-acetylgalactosaminyltransferase

Insects express arthro-series glycosphingolipids, which contain an alpha1,4-linked GalNAc residue. To determine the genetic basis for this linkage, we cloned a cDNA (CG17223) from Drosophila melanogaster encoding a protein with homology to mammalian alpha1,4-glycosyltransferases and expressed it in the yeast Pichia pastoris. Culture supernatants from the transformed yeast were found to display a novel UDP-GalNAc:GalNAcbeta1,4GlcNAcbeta1-R alpha-N-acetylgalactosaminyltransferase activity when using either a glycolipid, p-nitrophenylglycoside or an N-glycan carrying one or two terminal beta-N-acetylgalactosamine residues. NMR and MS in combination with glycosidase digestion and methylation analysis indicate that the cloned cDNA encodes an alpha1,4-N-acetylgalactosaminyltransferase. We hypothesize that this enzyme and its orthologues in other insects are required for the biosynthesis of the N5a and subsequent members of the arthro-series of glycolipids as well as of N-glycan receptors for Bacillus thuringiensis crystal toxin Cry1Ac.

N-glycan structures of pigeon IgG: a major serum glycoprotein containing Galalpha1-4 Gal termini

We had shown previously that all major glycoproteins of pigeon egg white contain Galalpha1-4Gal epitopes (Suzuki, N., Khoo, K. H., Chen, H. C., Johnson, J. R., and Lee, Y. C. (2001) J. Biol. Chem. 276, 23221-23229). We now report that Galalpha1-4Gal-bearing glycoproteins are also present in pigeon serum, lymphocytes, and liver, as probed by Western blot with Griffonia simplicifolia-I lectin (specific for terminal alpha-Gal) and anti-P1 (specific for Galalpha1-4Galbeta1-4GlcNAcbeta1-) monoclonal antibody. One of the major glycoproteins from pigeon plasma was identified as IgG (also known as IgY), which has Galalpha1-4Gal in its heavy chains. High pressure liquid chromatography, mass spectrometric (MS), and MS/MS analyses revealed that N-glycans of pigeon serum IgG included (i) high mannose-type (33.3%), (ii) disialylated biantennary complex-type (19.2%), and (iii) alpha-galactosylated complex-type N-glycans (47.5%). Bi- and tri-antennary oligosaccharides with bisecting GlcNAc and alpha1-6 Fuc on the Asn-linked GlcNAc were abundant among N-glycans possessing terminal Galalpha1-4Gal sequences. Moreover, MS/MS analysis identified Galalpha1-4Galbeta1-4Galbeta1-4GlcNAc branch terminals, which are not found in pigeon egg white glycoproteins. An additional interesting aspect is that about two-thirds of high mannose-type N-glycans from pigeon IgG were monoglucosylated. Comparison of the N-glycan structures with chicken and quail IgG indicated that the presence of high mannose-type oligosaccharides may be a characteristic of these avian IgG.

N-glycan structures from the major glycoproteins of pigeon egg white: predominance of terminal Galalpha(1)Gal

N-Glycans from major glycoproteins of pigeon egg white (ovotransferrin, ovomucoid, and ovalbumins) were enzymatically released and were reductively aminated with 2-aminopyridine, separated, and structurally characterized by mass spectrometry and a three-dimensional mapping technique using three different columns of high performance liquid chromatography (HPLC) (Takahashi, N., Nakagawa, H., Fujikawa, K., Kawamura, Y., and Tomiya, N. (1995) Anal. Biochem. 226, 139-146). Twenty-five major N-glycan structures, all of them hitherto unknown, were identified as pyridylamino derivatives. Of these, 13 were neutral, 10 were monosialyl, and 2 were disialyl oligosaccharides. All N-glycans contain from one to four Galalpha(1,4)Galbeta(1,4) sequences at the nonreducing terminal positions and are devoid of fucose residues. N-Acetylneuraminic acids were alpha(2,6)-linked only to beta-galactose. The HPLC profiles of the N-glycans from four different glycoproteins were qualitatively very similar to each other, but not identical in the peak distributions. Monosialyl glycans were most abundant in all four glycoproteins, followed by neutral glycans. Disialyl glycans were lowest in ovotransferrin, and highest in ovomucoid. Triantennary structures with bisecting GlcNAc were predominant in ovotransferrin, and tetra-antennary (with and without bisecting GlcNAc-containing) structures were predominant in other glycoproteins. Penta-antennary structures (with a sialic acid and without bisecting GlcNAc residue) were also found in small quantities in all four glycoproteins. In contrast to the chicken egg white counterparts, which contain mostly high mannose and hybrid types, all N-glycan structures in the major pigeon egg white glycoproteins are complex type.

Carbohydrate-carbohydrate binding of ganglioside to integrin alpha(5) modulates alpha(5)beta(1) function

Gangliosides GT1b and GD3, components of keratinocyte membranes, inhibit keratinocyte adhesion to fibronectin. Although ganglioside sialylation is known to be important, the mechanism of inhibition is unknown. Using purified insect recombinant alpha(5) and beta(1) proteins and alpha(5)beta(1) integrin from lysed keratinocyte-derived SCC12 cells, we have shown that GT1b and GD3 inhibit the binding of alpha(5)beta(1) to fibronectin. Co-immunoprecipitation of GT1b and alpha(5)beta(1) from SCC12 cells and direct binding of GT1b and GD3 to affinity-purified alpha(5)beta(1) from SCC12 cells and insect recombinant alpha(5)beta(1), particularly the alpha(5) subunit, further suggest interaction between ganglioside and alpha(5)beta(1). The carbohydrate moieties of integrin appear to be critical since gangliosides are unable to bind deglycosylated forms of alpha(5)beta(1) from SCC12 and insect cells or poorly glycosylated recombinant alpha(5)beta(1) from Escherichia coli cells. The GT1b-alpha(5)beta(1) interaction is inhibited by concanavalin A, suggesting that GT1b binds to mannose structures in alpha(5)beta(1). The preferential binding of GT1b to high mannose rather than reduced mannose ovalbumin further implicates the binding of GT1b to mannose structures. These data provide evidence that highly sialylated gangliosides regulate alpha(5)beta(1)-mediated adhesion of epithelial cells to fibronectin through carbohydrate-carbohydrate interactions between GT1b and the alpha(5) subunit of alpha(5)beta(1) integrin.

Molecular basis for the p phenotype. Identification of distinct and multiple mutations in the alpha 1,4-galactosyltransferase gene in Swedish and Japanese individuals

p phenotype individuals lack both P(k) (Gb3) and P (Gb4) glycolipid antigens of the P blood group system. To explore the molecular basis for this phenotype, DNA sequences of Gb3 synthase (alpha1, 4-galactosyltransferase; alpha1,4Gal-T) in six p phenotype individuals from Japan and Sweden were analyzed. A missense mutation P251L and a nonsense mutation W261stop in three and one Japanese indivuiduals, respectively, and missense mutations M183K and G187D in one each of two Swedish p individuals were found, indicating that p individuals from Japan and Sweden have distinct and multiple homozygous point mutations in the coding region. In the function analysis of the mutated alpha1,4Gal-Ts by the transfection of the expression vectors, P251L and M183K mutations showed complete loss of enzyme function, and W261stop and G187D mutations resulted in the marginal activity. BLAST analysis of homologous sequences of alpha1, 4Gal-T revealed that three residues, Met(183), Gly(187), and Pro(251), at which missense mutations were found, were highly conserved among all species examined, suggesting their importance for the function of alpha1,4Gal-T.

Cloning of Gb3 synthase, the key enzyme in globo-series glycosphingolipid synthesis, predicts a family of alpha 1, 4-glycosyltransferases conserved in plants, insects, and mammals

We have cloned Gb(3) synthase, the key alpha1, 4-galactosyltransferase in globo-series glycosphingolipid (GSL) synthesis, via a phenotypic screen, which previously yielded iGb(3) synthase, the alpha1,3-galactosyltransferase required in isoglobo-series GSL (Keusch, J. J., Manzella, S. M., Nyame, K. A., Cummings, R. D., and Baenziger, J. U. (2000) J. Biol. Chem. 33). Both transferases act on lactosylceramide, Galbeta1,4Glcbeta1Cer (LacCer), to produce Gb(3) (Galalpha1,4LacCer) or iGb(3) (Galalpha1, 3LacCer), respectively. GalNAc can be added sequentially to either Gb(3) or iGb(3) yielding globoside and Forssman from Gb(3), and isogloboside and isoForssman from iGb(3). Gb(3) synthase is not homologous to iGb(3) synthase but shows 43% identity to a human alpha1,4GlcNAc transferase that transfers a UDP-sugar in an alpha1, 4-linkage to a beta-linked Gal found in mucin. Extensive homology (35% identity) is also present between Gb(3) synthase and genes in Drosophila melanogaster and Arabidopsis thaliana, supporting conserved expression of an alpha1,4-glycosyltransferase, possibly Gb(3) synthase, throughout evolution. The isolated Gb(3) synthase cDNA encodes a type II transmembrane glycosyltransferase of 360 amino acids. The highest tissue expression of Gb(3) synthase RNA is found in the kidney, mesenteric lymph node, spleen, and brain. Gb(3) glycolipid, also called P(k) antigen or CD77, is a known receptor for verotoxins. CHO cells that do not express Gb(3) and are resistant to verotoxin become susceptible to the toxin following transfection with Gb(3) synthase cDNA.

Cloning and expression of the histo-blood group Pk UDP-galactose: Ga1beta-4G1cbeta1-cer alpha1, 4-galactosyltransferase. Molecular genetic basis of the p phenotype

The molecular genetic basis of the P histo-blood group system has eluded characterization despite extensive studies of the biosynthesis of the P(1), P, and P(k) glycolipids. The main controversy has been whether a single or two distinct UDP-Gal:Galbeta1-R 4-alpha-galactosyltransferases catalyze the syntheses of the structurally related P(1) and P(k) antigens. The P(1) polymorphism is linked to 22q11.3-ter. Data base searches with the coding region of an alpha4GlcNAc-transferase identified a novel homologous gene at 22q13.2 designated alpha4Gal-T1. Expression of full coding constructs of alpha4Gal-T1 in insect cells revealed it encoded P(k) but not P(1) synthase activity. Northern analysis showed expression of the transcript correlating with P(k) synthase activity and antigen expression in human B cell lines. Transfection of P(k)-negative Namalwa cells with alpha4Gal-T1 resulted in strong P(k) expression. A single homozygous missense mutation, M183K, was found in six Swedish individuals of the rare p phenotype, confirming that alpha4Gal-T1 represented the P(k) gene. Sequence analysis of the coding region of alpha4Gal-T1 in P(1)+/- individuals did not reveal polymorphisms correlating with P(1)P(2) typing.

O-glycosylation potential of lepidopteran insect cell lines

The enzyme activities involved in O-glycosylation have been studied in three insect cell lines, Spodoptera frugiperda (Sf-9), Mamestra brassicae (Mb) and Trichoplusia ni (Tn) cultured in two different serum-free media. The structural features of O-glycoproteins in these insect cells were investigated using a panel of lectins and the glycosyltransferase activities involved in O-glycan biosynthesis of insect cells were measured (i.e., UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase, UDP-Gal:core-1 beta1, 3-galactosyltransferase, CMP-NeuAc:Galbeta1-3GalNAc alpha2, 3-sialyltransferase, and UDP-Gal:Galbeta1-3GalNAc alpha1, 4-galactosyltransferase activities). First, we show that O-glycosylation potential depends on cell type. All three lepidopteran cell lines express GalNAcalpha-O-Ser/Thr antigen, which is recognized by soy bean agglutinin and reflects high UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase activity. Capillary electrophoresis and mass spectrometry studies revealed the presence of at least two different UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferases in these insect cells. Only some O-linked GalNAc residues are further processed by the addition of beta1,3-linked Gal residues to form T-antigen, as shown by the binding of peanut agglutinin. This reflects relative low levels of UDP-Gal:core-1 beta1,3-galactosyltransferase in insect cells, as compared to those observed in mammalian control cells. In addition, we detected strong binding of Bandeiraea simplicifolia lectin-I isolectin B4 to Mamestra brassicae endogenous glycoproteins, which suggests a high activity of a UDP-Gal:Galbeta1-3GalNAc alpha1, 4-galactosyltransferase. This explains the absence of PNA binding to Mamestra brassicae glycoproteins. Furthermore, our results substantiated that there is no sialyltransferase activity and, therefore, no terminal sialic acid production by these cell lines. Finally, we found that the culture medium influences the O-glycosylation potential of each cell line.

Insect cells as hosts for the expression of recombinant glycoproteins

Baculovirus-mediated expression in insect cells has become well-established for the production of recombinant glycoproteins. Its frequent use arises from the relative ease and speed with which a heterologous protein can be expressed on the laboratory scale and the high chance of obtaining a biologically active protein. In addition to Spodoptera frugiperda Sf9 cells, which are probably the most widely used insect cell line, other mainly lepidopteran cell lines are exploited for protein expression. Recombinant baculovirus is the usual vector for the expression of foreign genes but stable transfection of - especially dipteran - insect cells presents an interesting alternative. Insect cells can be grown on serum free media which is an advantage in terms of costs as well as of biosafety. For large scale culture, conditions have been developed which meet the special requirements of insect cells. With regard to protein folding and post-translational processing, insect cells are second only to mammalian cell lines. Evidence is presented that many processing events known in mammalian systems do also occur in insects. In this review, emphasis is laid, however, on protein glycosylation, particularly N-glycosylation, which in insects differs in many respects from that in mammals. For instance, truncated oligosaccharides containing just three or even only two mannose residues and sometimes fucose have been found on expressed proteins. These small structures can be explained by post-synthetic trimming reactions. Indeed, cell lines having a low level of N-acetyl-beta-glucosaminidase, e.g. Estigmene acrea cells, produce N- glycans with non-reducing terminal N-acetylglucosamine residues. The Trichoplusia ni cell line TN-5B1-4 was even found to produce small amounts of galactose terminated N-glycans. However, there appears to be no significant sialylation of N-glycans in insect cells. Insect cells expressed glycoproteins may, though, be alpha1,3-fucosylated on the reducing-terminal GlcNAc residue. This type of fucosylation renders the N-glycans on one hand resistant to hydrolysis with PNGase F and on the other immunogenic. Even in the absence of alpha1,3-fucosylation, the truncated N-glycans of glycoproteins produced in insect cells constitute a barrier to their use as therapeutics. Attempts and strategies to "mammalianise" the N-glycosylation capacity of insect cells are discussed.