Bovine colostrum CMP-NeuAc:Gal beta(1-->4)GlcNAc-R alpha(2-->6)-sialyltransferase is involved in the synthesis of the terminal NeuAc alpha(2-->6)GalNAc beta(1-->4)GlcNAc sequence occurring on N-linked glycans of bovine milk glycoproteins

N-glycan profiling of bovine follicular fluid at key dominant follicle developmental stages

Follicular fluid (FF), an important microenvironment for the development of oocytes, contains many proteins that are glycosylated withN-linked glycans. This study aimed i) to present an initial analysis of theN-linked glycan profile of bovine FF using hydrophilic interaction liquid chromatography, anion exchange chromatography, high performance liquid chromatography (HPLC)-based separations and subsequent liquid chromatography–mass spectrometry/mass spectrometry analysis; ii) to determine differences in theN-glycan profile between FF from dominant and subordinate follicles from dairy heifers and lactating dairy cows and iii) to identify alterations in theN-glycan profile of FF during preovulatory follicle development using newly selected, differentiated (preovulatory) and luteinised dominant follicles from dairy heifers and lactating cows. We found that the majority of glycans on bovine FF are based on biantennary hypersialylated structures, where the glycans are sialylated on both the galactose andN-acetylglucosamine terminal sugars. A comparison of FFN-glycans from cows and heifers indicated higher levels of nonsialylated glycans with a lower proportion of sialylated glycans in cows than in heifers. Overall, as the follicle develops from Selection, Differentiation and Luteinisation in both cows and heifers, there is an overall decrease in sialylated structures on FFN-glycans.

Construction and characterization of stably transfected BHK-21 cells with human-type sialylation characteristic

The human Golgi enzyme CMP-NeuAc:Gal(beta1-4)GlcNAc-R alpha2,6-sialyltransferase (ST6N) was stably coexpressed with human erythropoietin (EPO) from a BHK-21A cell line. The cell line was characterized with respect to the expression and in vitro activity of the ST6N and the endogenous alpha2,3-sialyltransferase. Detailed structural analysis of the N-linked carbohydrates of the rhuEPO expressed from the new cell line was performed by HPAE-PAD-mapping, MALDI/TOF-MS and methylation analysis after purification of the recombinant protein by immunoaffinity chromatography. This is the first report describing that the human alpha2,6-sialyltransferase is capable of sialylating, apart from Gal(beta1-4)GlcNAc-R, also GalNAc(beta1-4)GlcNAc-R motifs in vivo, which is not the case for the endogenous BHK-cell alpha2,3-sialyltransferase.

Novel Poly-GalNAcβ1–4GlcNAc (LacdiNAc) and Fucosylated Poly-LacdiNAc N-Glycans from Mammalian Cells Expressing β1,4-N-Acetylgalactosaminyltransferase and α1,3-Fucosyltransferase

Glycans containing the GalNAcbeta1-4GlcNAc (LacdiNAc or LDN) motif are expressed by many invertebrates, but this motif also occurs in vertebrates and is found on several mammalian glycoprotein hormones. This motif contrasts with the more commonly occurring Galbeta1-4GlcNAc (LacNAc or LN) motif. To better understand LDN biosynthesis and regulation, we stably expressed the cDNA encoding the Caenorhabditis elegans beta1,4-N-acetylgalactosaminyltransferase (GalNAcT), which generates LDN in vitro, in Chinese hamster ovary (CHO) Lec8 cells, to establish L8-GalNAcT CHO cells. The glycan structures from these cells were determined by mass spectrometry and linkage analysis. The L8-GalNAcT cell line produces complex-type N-glycans quantitatively bearing LDN structures on their antennae. Unexpectedly, most of these complex-type N-glycans contain novel "poly-LDN" structures consisting of repeating LDN motifs (-3GalNAcbeta1-4GlcNAcbeta1-)n. These novel structures are in contrast to the well known poly-LN structures consisting of repeating LN motifs (-3Galbeta1-4GlcNAcbeta1-)n. We also stably expressed human alpha1,3-fucosyltransferase IX in the L8-GalNAcT cells to establish a new cell line, L8-GalNAcT-FucT. These cells produce complex-type N-glycans with alpha1,3-fucosylated LDN (LDNF) GalNAcbeta1-4(Fucalpha1-3)GlcNAcbeta1-R as well as novel "poly-LDNF" structures (-3GalNAcbeta1-4(Fucalpha 1-3)GlcNAcbeta1-)n. The ability of these cell lines to generate glycoprotein hormones with LDN-containing N-glycans was studied by expressing a recombinant form of the common alpha-subunit in L8-GalNAcT cells. The alpha-subunit N-glycans carried LDN structures, which were further modified by co-expression of the human GalNAc 4-sulfotransferase I, which generates SO4-4GalNAcbeta1-4GlcNAc-R. Thus, the generation of these stable mammalian cells will facilitate future studies on the biological activities and properties of LDN-related structures in glycoproteins.

Functional characterization of Drosophila sialyltransferase

Sialylation is an important carbohydrate modification of glycoconjugates in the deuterostome lineage of animals. By contrast, the evidence for sialylation in protostomes has been scarce and somewhat controversial. In the present study, we characterize a Drosophila sialyltransferase gene, thus providing experimental evidence for the presence of sialylation in protostomes. This gene encodes a functional alpha2-6-sialyltransferase (SiaT) that is closely related to the vertebrate ST6Gal sialyltransferase family, indicating an ancient evolutionary origin for this family. Characterization of recombinant, purified Drosophila SiaT revealed a novel acceptor specificity as it exhibits highest activity toward GalNAcbeta1-4GlcNAc carbohydrate structures at the non-reducing termini of oligosaccharides and glycoprotein glycans. Oligosaccharides are preferred over glycoproteins as acceptors, and no activity toward glycolipid acceptors was detected. Recombinant Drosophila SiaT expressed in cultured insect cells possesses in vivo and in vitro autosialylation activity toward beta-linked GalNAc termini of its own N-linked glycans, thus representing the first example of a sialylated insect glycoconjugate. In situ hybridization revealed that Drosophila SiaT is expressed during embryonic development in a tissue- and stage-specific fashion, with elevated expression in a subset of cells within the central nervous system. The identification of a SiaT in Drosophila provides a new evolutionary perspective for considering the diverse functions of sialylation and, through the powerful genetic tools available in this system, a means of elucidating functions for sialylation in protostomes.

Identification and functional expression of a second human beta-galactoside alpha2,6-sialyltransferase, ST6Gal II

BLAST analysis of the human and mouse genome sequence databases using the sequence of the human CMP-sialic acid:beta-galactoside alpha-2,6-sialyltransferase cDNA (hST6Gal I, EC2.4.99.1) as a probe allowed us to identify a putative sialyltransferase gene on chromosome 2. The sequence of the corresponding cDNA was also found as an expressed sequence tag of human brain. This gene contained a 1590 bp open reading frame divided in five exons and the deduced amino-acid sequence didn't correspond to any sialyltransferase already known in other species. Multiple sequence alignment and subsequent phylogenic analysis showed that this new enzyme belonged to the ST6Gal subfamily and shared 48% identity with hST6Gal-I. Consequently, we named this new sialyltransferase ST6Gal II. A construction in pFlag vector transfected in COS-7 cells gave raise to a soluble active form of ST6Gal II. Enzymatic assays indicate that the best acceptor substrate of ST6Gal II was the free disaccharide Galbeta1-4GlcNAc structure whereas ST6Gal I preferred Galbeta1-4GlcNAc-R disaccharide sequence linked to a protein. The alpha2,6-linkage was confirmed by the increase of Sambucus nigra agglutinin-lectin binding to the cell surface of CHO transfected with the cDNA encoding ST6Gal II and by specific sialidases treatment. In addition, the ST6Gal II gene showed a very tissue specific pattern of expression because it was found essentially in brain whereas ST6Gal I gene is ubiquitously expressed.

alpha 2,3-Sialylation of terminal GalNAc beta 1-3Gal determinants by ST3Gal II reveals the multifunctionality of the enzyme. The resulting Neu5Ac alpha 2-3GalNAc linkage is resistant to sialidases from Newcastle disease virus and Streptococcus pneumoniae

Enzymatic alpha 2,3-sialylation of GalNAc has not been described previously, although some glycoconjugates containing alpha 2,3-sialylated GalNAc residues have been reported. In the present experiments, recombinant soluble alpha 2,3-sialyltransferase ST3Gal II efficiently sialylated the X(2) pentasaccharide GalNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc, globo-N-tetraose GalNAc beta 1-3Gal alpha 1-4Gal beta 1-4Glc, and the disaccharide GalNAc beta 1-3Gal in vitro. The purified products were identified as Neu5Ac alpha 2-3GalNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc, Neu5Ac alpha 2-3GalNAc beta 1-3Gal alpha 1-4Gal beta 1-4Glc, and Neu5Ac alpha 2-3GalNAc beta 1-3Gal, respectively, by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, enzymatic degradations, and one- and two-dimensional NMR-spectroscopy. In particular, the presence of the Neu5Ac alpha 2-3GalNAc linkage was firmly established in all three products by a long range correlation between Neu5Ac C2 and GalNAc H3 in heteronuclear multiple bond correlation spectra. Collectively, the data describe the first successful sialyltransfer reactions to the 3-position of GalNAc in any acceptor. Previously, ST3Gal II has been shown to transfer to the Gal beta 1-3GalNAc determinant. Consequently, the present data show that the enzyme is multifunctional, and could be renamed ST3Gal(NAc) II. In contrast to ST3Gal II, ST3Gal III did not transfer to the X(2) pentasaccharide. The Neu5Ac alpha 2-3GalNAc linkage of sialyl X(2) was cleaved by sialidases from Arthrobacter ureafaciens and Clostridium perfringens, but resisted the action of sialidases from Newcastle disease virus and Streptococcus pneumoniae. Therefore, the latter two enzymes cannot be used to differentiate between Neu5Ac alpha 2-3GalNAc and Neu5Ac alpha 2-6GalNAc linkages, as has been assumed previously.

Molecular cloning, expression and exon/intron organization of the bovine beta-galactoside alpha2,6-sialyltransferase gene

In this study, we report the first isolation and characterization of a bovine sialyltransferase gene. Bovine cDNAs prepared from different tissues contain an open-reading frame encoding a 405 amino acid sequence showing 83%, 75%, and 60% identity with human, murine, and chicken ST6Gal I (beta-galactoside alpha2,6-sialyltransferase) sequences, respectively. When transfected into COS-7 cells, a recombinant enzyme was obtained which catalyzed the in vitro alpha2, 6-sialylation of LacNAc (NeuAcalpha2-6Galbeta1-4GlcNAc) and LacdiNAc (NeuAcalpha2-6GalNAcbeta1-4GlcNAc) acceptor substrates. The K (m) values were 2.8 and 6.9 mM, respectively. Different relative efficiencies (Vmax/Km) for the two precursors (36 for LacNAc and 4.3 for LacdiNAc) were observed. Bovine ST6Gal I gene consists of four 5'-untranslated exons E(-2) to E(1), and five coding exons from E(2) to E(6). This later carries a 3'-untranslated region of 2. 7 kb. Gene sequence spans at least 80 kb of genomic DNA. Two processed pseudogenes have been identified. They are 94.3 and 95.6% similar to the bovine cDNA, respectively. Three families of mRNA isoforms were isolated. They differed by their 5'-untranslated regions and could be generated by three tissue-specific promoters. Family 1 is made up of exons E(-2) and E(1) to E(6), family 2 of exons E(-1) to E(6), and family 3 of exons E(1) to E(6). Tissular distribution of transcript families appears noticeably different than those described in human and rat.

Genetic engineering of recombinant glycoproteins and the glycosylation pathway in mammalian host cells

The analysis of many natural glycoproteins and their recombinant counterparts from mammalian hosts has revealed that the basic oligosaccharide structures and the site occupancy of glycosylated polypeptides are primarily dictated by the protein conformation. The equipment of many frequently used host cells (e.g. BHK-21 and CHO-cells) with glycosyltransferases, nucleotide-sugar synthases and transporters appears to be sufficient to guarantee complex-type glycosylation of recombinant proteins with a high degree of terminal alpha2-3 sialylation even under high expression conditions. Some human tissue-specific terminal carbohydrate motifs are not synthesized by these cells since they lack the proper sugar-transferring enzymes (e.g. alpha1-3/4 fucosyltransferases, alpha2-6 sialyltransferases). Glycosylation engineering of these hosts by stable transfection with genes encoding terminal human glycosyltransferases allows to obtain products with tailored (human tissue-specific) glycosylation in high yields. Using site-directed mutagenesis, unglycosylated polypeptides can be successfully converted in N- and/or O-glycoproteins by transferring glycosylation domains (consisting of 7-17 amino acids) from donor glycoproteins to different loop regions of acceptor proteins. The genetic engineering of glycoproteins and of host cell lines are considered to provide a versatile tool to obtain therapeutic glyco-products with novel/improved in-vivo properties, e.g. by introduction of specific tissue-targeting signals by a rational design of terminal glycosylation motifs.

Bovine mammary gland UDP-GalNAc:GlcNAcbeta-R beta1-->4-N-acetylgalactosaminyltransferase is glycoprotein hormone nonspecific and shows interaction with alpha-lactalbumin

We have identified a novel N -acetylgalactosaminyltransferase activity in lactating bovine mammary gland membranes. Acceptor specificity studies and analysis of products obtained in vitro by 400 MHz1H-NMR spectroscopy revealed that the enzyme catalyses the transfer of N -acetylgalactosamine (GalNAc) from UDP-GalNAc to acceptor substrates carrying a terminal, beta-linked N -acetylglucosamine (GlcNAc) residue and establishes a beta1-->4-linkage forming a GalNAcbeta1-->4GlcNAc ( N, N '-diacetyllactosediamine, lacdiNAc) unit. Therefore, the enzyme can be identified as a UDP-GalNAc:GlcNAcbeta-R beta1-->4-N-acetylgalactosaminyltransferase (beta4-GalNAcT). This enzyme resembles invertebrate beta4-GalNAcT as well as mammalian beta4-galactosyltransferase (beta4-GalT) in acceptor specificity. It can, however, be clearly distinguished from the pituitary hormone-specific beta4-GalNAcT by its incapability of acting with an elevated activity on a glycoprotein substrate carrying a hormone-specific peptide motif. Furthermore, the GalNAcT activity appeared not to be due to a promiscuous action of a beta4-GalT as could be demonstrated by comparing the beta4-GalNAcT and beta4-GalT activities of the mammary gland, bovine colostrum, and purified beta4-GalT, by competition studies with UDP-GalNAc and UDP-Gal, and by use of an anti-beta4-GalT polyclonal inhibiting antibody. Interestingly, under conditions where mammalian beta4-GalT forms with alpha-lactalbumin (alpha-LA) the lactose synthase complex, the mammary gland beta4-GalNAcT was similarly induced by alpha-LA to act on Glc with an increased efficiency yielding the lactose analog GalNAcbeta1-->4Glc. This enzyme thus forms the second example of a mammalian glycosyltransferase the specificity of which can be modified by this milk protein. It is proposed that the mammary gland beta4-GalNAcT functions in the synthesis of lacdiNAc-based, complex-type glycans frequently occurring on bovine milk glycoproteins. The action of this enzyme is to be considered when aiming at the production of properly glycosylated protein biopharmaceuticals in the milk of transgenic dairy animals.

Enzyme-assisted synthesis of Asn-linked diantennary oligosaccharides occurring on glycodelin A

The preparation of a series of sialylated and fucosylated N,N'-diacetyllactosediamine-type diantennary glycopeptides is reported. By sequential enzymatic action of jack bean beta-galactosidase, snail beta 4-N-acetyl-galactosaminyltransferase, bovine colostrum alpha 6-sialyltransferase and human milk alpha 3-fucosyltransferase, a diantennary glycopeptide obtained from asialo fibrinogen was converted at a 5-mumol scale to a series of structures occurring on the glycoprotein glycodelin A, which potentially inhibit human sperm-egg binding.

Developmental regulation of a pregnancy-specific oligosaccharide structure, NeuAcalpha2,6GalNAcbeta1,4GlcNAc, on select members of the rat placental prolactin family

Successful pregnancy is dependent upon an array of signaling proteins secreted by the trophoblast cells of the placenta. Among these is a group of proteins related to pituitary prolactin, known as the prolactin/growth hormone family. These proteins are expressed at specific times during gestation and synthesized in distinct trophoblast cell types in the rat placenta. We report here that select members of this family, prolactin-like protein (PLP-A), PLP-B, PLP-C, decidual/trophoblast PRP, and placental lactogen I variant, only which are expressed in the spongiotrophoblast, late in rat placental development bear Asn-linked oligosaccharides terminating with NeuAcalpha2,6GalNAcbeta1,4GlcNAcbeta-R. This reflects the concurrent expression of these prolactin/growth hormone family members with the peptide-specific beta1,4GalNAc-transferase and an alpha2,6-sialyltransferase, which can add sialic acid to terminal beta1,4-linked GalNAc. We have determined that at least one of the prolactin-like proteins, PLP-A, is recognized by the protein-specific GalNAc-transferase. The presence of NeuAcalpha2, 6GalNAcbeta1,4GlcNAcbeta-R on only a limited number of glycoproteins synthesized by the spongiotrophoblasts between mid gestation and birth reflects the need for both the GalNAc-transferase and the peptide recognition determinant for efficient addition of GalNAc. Thus, expression of the GalNAc-transferase and specific members of the prolactin/growth hormone family is developmentally regulated in the rat placenta, suggesting a physiological role for the terminal NeuAcalpha2,6GalNAcbeta1,4GlcNAcbeta-R sequence on Asn-linked oligosaccharides of these proteins.

Alpha-lactalbumin affects the acceptor specificity of Lymnaea stagnalis albumen gland UDP-GalNAc:GlcNAc beta-R beta 1-->4-N-acetylgalactosaminyltransferase: synthesis of GalNAc beta 1-->4Glc

The N,N'-diacetyllactosediamine (lacdiNAc) pathway of complex-type oligosaccharide synthesis is controlled by a UDP-GalNAc:GlcNAc beta-R beta 1-->4-N-acetylgalac-tesaminyltransferase (beta 4-GalNAcT) that acts analogously to the common UDP-Gal:GlcNAc beta-R beta 1-->4-galactosyltransferase (beta 4-GalT). LacdiNAc-based chains particularly occur in invertebrates and cognate beta 4-GalNAcTs have been identified in the snail Lymnaea stagnalis, in two schistosomal species, and in several lepldopteran insect cell lines. Because of the similarity in reactions catalyzed by both enzymes, we investigated whether L. stagnalis albumen gland beta 4-GalNAcT would share with mammalian beta 4-GalT the property of interacting with alpha-lactalbumin (alpha-LA), a protein that only occurs in the lactating mammary gland, to form a complex in which the specificity of the enzyme is changed. It was found that, under conditions where beta 4-GalT forms the lactose synthase complex with alpha-LA, the snail beta 4-GalNAcT was induced by this protein to act on Glc with a > 100-fold increased efficiency, resulting in the formation of the lactose analog GalNAc beta 1-->4Glc. This forms the second example of a glycosyltransferase, the specificity of which can be altered by a modifier protein. So far, however, no protein fraction could be isolated from L. stagnalis that could likewise interact with the beta 4-GalNAcT. Neither had lysozyme c, a protein that is homologous to alpha-LA, an effect on the specificity of the enzyme. These results raise the question of how the capability to interact with alpha-LA has been conserved in the snail enzyme during evolution without any apparent selective pressure. They also suggest that snail beta 4-GalNAcT and mammalian beta 4-GalT show similarity at a molecular level and allows the identification of the beta 4-GalNAcT as a candidate member of the beta 4-GalT family.

Differential expression of GalNAc-4-sulfotransferase and GalNAc-transferase results in distinct glycoforms of carbonic anhydrase VI in parotid and submaxillary glands

Differential expression of glycosyltransferases has the potential to generate functionally distinct glycoforms of otherwise identical proteins. We have previously demonstrated the presence of unique oligosaccharides terminating with GalNAc-4-SO4 on the pituitary glycoproteins lutropin (LH), thyroid stimulating hormone (TSH), and pro-opiomelanocortin (POMC). A glycoprotein hormone:GalNAc-transferase and a GalNAc-4-sulfotransferase are present in the pituitary and can account for the synthesis of these unique oligosaccharides on specific glycoproteins. Both transferases are coordinately expressed in a number of tissues in addition to pituitary, including submaxillary gland, lacrimal gland, and kidney, suggesting that additional glycoproteins bearing oligosaccharides terminating with GalNAc-4-SO4 are synthesized in these tissues. In this study we show that while the glycoprotein hormone:GalNAc-transferase and the GalNAc-4-sulfotransferase are coordinately expressed in bovine submaxillary gland, the GalNAc-transferase is expressed in the parotid gland in the absence of the GalNAc-4-sulfotransferase. The relative expression of these two transferases in submaxillary and parotid glands correlates with the presence of unique Asn-linked oligosaccharides on carbonic anhydrase VI (CA VI) synthesized in each of these tissues. The majority of Asn-linked oligosaccharides on CA VI synthesized in submaxillary gland terminate with GalNAc-4-SO4. In contrast, CA VI which is synthesized in bovine parotid gland bears oligosaccharides which terminate predominantly with beta 1,4-linked GalNAc which is not sulfated. The presence of different terminal residues on the Asn-linked oligosaccharides of submaxillary and parotid CA VI thus correlates with the complement of transferases in these glands and suggests differing biological roles for submaxillary and parotid CA VI.

Enzymic remodelling of the N- and O-linked carbohydrate chains of human chorionic gonadotropin. Effects on biological activity and receptor binding

The effects of altered terminal sequences in human chorionic gonadotropin (hCG) N- and O-linked glycans on receptor binding and signal transduction were analyzed using forms of hCG with remodelled carbohydrate chains. hCG derivatives were obtained by enzymic removal of the alpha 3-linked sialic acid residues followed by alpha 6-sialylation, alpha 3-galactosylation or alpha 3-fucosylation of uncovered Gal beta 1-->4GlcNAc (LacNAc) termini, or alpha 3-sialylation of Gal beta 1-->3GalNAc sequences. Also a form that carried GalNAc beta 1-->4-GlcNAc units, which are typical for pituitary hormone oligosaccharides, was derived by enzymic desialylation and degalactosylation followed by beta 4-N-acetylgalactosaminylation. The potency to stimulate testosterone production and the binding to the lutotropin/choriogonadotropin receptor of the preparations were compared with those of native and desialylated hCG (as-hCG). The decrease in bioactivity caused by desialylation of hCG was only restored upon alpha 6-sialylation of the Gal beta 1-->4GlcNAc beta 1-->-2Man alpha 1-->3Man branch of the N-linked glycans. This was without a major effect on receptor binding. Further alpha 6-sialylation, occurring at the Gal beta 1-->4GlcNAc beta 1-->2Man alpha 1-->6Man branch, resulted in a bioactivity below a level found with as-hCG, concomitant with a decreased receptor binding affinity. Similarly alpha 3-galactosylation of the Gal beta 1-->4GlcNAc beta 1-->2-Man alpha 1-->6Man branch yielded a hCG derivative that showed decreased bioactivity and receptor binding. alpha 3-Fucosylation of native as well as as-hCG also led to a decreased activity. Re-alpha 3-sialylation of the O-linked chains on as-hCG had little effect on the bioactivity and receptor binding. Hormone preparations with GalNAc beta 1-->4GlcNAc termini showed lower bioactivity and receptor affinity than as-hCG. It is concluded that the Gal beta 1-->4GlcNAc beta 1-->2Man alpha 1-->3Man- rather than the Gal beta 1-->4GlcNAc beta 1-->2-Man alpha 1-->6Man branch of the N-linked glycans on hCG plays an essential role in signal transduction, whereas the latter branch can potentially interfere with receptor binding. Furthermore attachment of sialic acid, but not of other sugars, to the first branch fulfils the requirement for the full expression of bioactivity, while sialylation of the O-linked chains is of minor importance.

Estrogen modulates expression of the glycosyltransferases that synthesize sulfated oligosaccharides on lutropin

The glycoprotein hormone lutropin (LH) bears oligosaccharides terminating with the sequence SO4-4-GalNAc beta 1,4GlcNAc beta 1,2 Man alpha. We have determined that estrogen actively modulates expression of the GalNAc- and sulfotransferases responsible for synthesis of sulfated oligosaccharides on LH alpha and beta subunits. Consequently, terminal glycosylation of LH oligosaccharides with GalNAc-4-SO4 is maintained when LH synthesis and secretion are markedly increased, as occurs during the midcycle surge and following ovariectomy. Maintenance of sulfated oligosaccharides on LH has important biologic consequences because LH circulatory half-life as well as biologic activity at the hormone receptor level are dramatically affected by glycosylation. To our knowledge, regulation of glycosyltransferase levels in response to specific stimuli has not been observed previously, further emphasizing the biologic significance of glycosylation for expression of LH bioactivity in vivo.

Conversion of GalNAc beta(1-4)GlcNAc beta-OMe into GalNAc beta (1-4)-[Fuc alpha(1-3)]GlcNAc beta-OMe using human milk alpha 3/4-fucosyltransferase. Synthesis of a novel terminal element in glycoprotein glycans

Incubation of GalNAc beta(1-4)GlcNAc beta-OMe with GDP-Fuc in the presence of human milk alpha 3/4-fucosyltransferase resulted in the formation of GalNAc beta(1-4)[Fuc alpha(1-3)]GlcNAc beta-OMe. Under conditions that led to complete alpha 3-fucosylation of Gal beta(1-4)GlcNAc beta-OEt, GalNAc beta(1-4)GlcNAc beta-OMe was fucosylated for more than 85%. For the identification of the isolated fucosylated products one- and two-dimensional 1H-NMR spectroscopy was applied. In vacuo molecular dynamics simulations of Gal beta(1-4)[Fuc alpha(1-3)]GlcNAc beta-OEt and GalNAc beta(1-4)[Fuc alpha(1-3)]GlcNAc beta-OMe using the CHARMm based force field CHEAT, demonstrated only small differences between the conformations of these compounds. This illustrates the minor conformational influence of the substituent at C-2', i.e. a hydroxyl function versus a N-acetyl group.