Aß-affected pathogenic induction of S-nitrosylation of OGT and identification of Cys-NO linkage triplet.

Mechanistic link of protein hypo-O-GlcNAcylation to the pathogenesis of Alzheimer's disease (AD) remains unclear. Here, we found that S-nitrosylation of O-linked N-acetylglucosaminyltransferase (SNO-OGT) was induced by ß-amyloid peptide (Aß) exposure to SK-N-MC and SK-N-SH human neuroblastoma cells. Subsequently, Aß-induced SNO-OGT led to protein hypo-O-GlcNAcylation globally including tau hypo-O-GlcNAcylation. Our results support that underlying mechanism for induction of SNO-OGT comprises the concerted action of Aß-triggered Ca2+ entry into cells and nNOS-catalyzed NO production. Intriguingly, OGT was found to be associated with nNOS and its association was enhanced during Aß treatment. In parallel with SNO-OGT-mediated tau hypo-O-GlcNAcylation, Aß led to SNO-Akt-mediated GSK3ß activation for tau phosphorylation, suggesting that tau hyperphosphorylation is established by synergistic connection between SNO-OGT and GSK3ß activation. We also observed that Aß-neurotoxicity including both reactive oxygen species (ROS) production and cell death was amplified with DON treatment, whereas it was restored by PUGNAc treatment, GlcNH2 treatment or OGT overexpression. Early time-course Aß-monitoring assay revealed that premaintained hyper-O-GlcNAcylation inside cells blocked not only Aß-triggered Ca2+ entry into cells but also induction of SNO-OGT and SNO-Akt. Together, these findings suggest that induction of SNO-OGT by Aß exposure is a pathogenic mechanism to cause cellular hypo-O-GlcNAcylation by which Aß neurotoxicity is executed, and conversely, hyper-O-GlcNAcylation within cells can defend against Aß neurotoxicity. Furthermore, our Cys mapping demonstrates that cysteine-nitric oxide (Cys-NO) linkages in SNO-OGT occur at triple Cys845, Cys921, and Cys965 residues in C-terminal catalytic domain (C-CAT), suggesting that Cys-NO linkage triplet in SNO-OGT is associated with null OGT activity.

Heat-Shock Triggers Inverted Induction of Hypo-S-Nitrosylation and Hyper-O-GlcNAcylation.

INTRODUCTION: Protein S-nitrosylation (SNO) and O-GlcNAcylation are important posttranslational modifications. The biological connection between SNO and O-GlcNAcylation is not clear. OBJECTIVE: We aim to identify the crosstalk between SNO and O-GlcNAcylation during heat-shock. METHODS: Ex vivo heat-shock on mouse tissues together with in vitro heat-shock on culture cells was performed and global levels of SNO and O-GlcNAcylation were analyzed with Biotin-switch assay (BSA) and RL2 immunoblots. RESULTS: Heat-shock induces hypo-SNO in parallel with hyper-O-GlcNAcylation. Inverted induction of hypo-SNO and hyper-O-GlcNAcylation is globally progressed in a time-dependent manner. DISCUSSION: Moreover, heat-shock ubiquitously facilitates S-denitrosylation (SdeNO) of endogenous SNO-proteins including SNO-OGT, SNO-Hsp70, SNO-Hsp90, SNO-Akt, and SNOactin. Particularly, SdeNO of SNO-OGT leads to enhanced OGT activity. CONCLUSION: These findings provide mechanistic evidence that heat-shock triggers SdeNO of SNOOGT by which OGT activity is up-regulated, resulting in hyper-O-GlcNAcylation.

Denitrosylation of S-nitrosylated OGT is triggered in LPS-stimulated innate immune response.

O-linked N-acetylglucosaminyltransferase (OGT)-mediated protein O-GlcNAcylation has been revealing various aspects of functional significance in biological processes, such as cellular signaling and activation of immune system. We found that OGT is maintained as S-nitrosylated form in resting cells, and its denitrosylation is triggered in innate immune response of lipopolysaccharide (LPS)-treated macrophage cells. S-nitrosylation of OGT strongly inhibits its catalytic activity up to more than 80% of native OGT, and denitrosylation of OGT leads to protein hyper-O-GlcNAcylation. Furthermore, blockage of increased protein O-GlcNAcylation results in significant loss of nitric oxide and cytokine production. We propose that denitrosylation of S-nitrosylated OGT is a direct mechanism for upregulation of OGT activity by which immune defense is critically controlled in LPS-stimulated innate immune response.

Selective α-glucosidase substrates and inhibitors containing short aromatic peptidyl moieties.

We constructed a library of sugar-dipeptide conjugate to find out the best complementary against hydrophobic pocket of α-glucosidase. The best substrate showed 150-fold improved K(m) value relative p-acetaminophenyl-α-D-glucopyranoside for α-glucosidase from Bacillus stearothermophillus. Using information from the complementary, we synthesized sp-WY and ß-Glc-sp-WY, which selectivity inhibited the cognate enzyme.

Generation of novel chimeric LacdiNAcS by gene fusion of alpha-lactalbumin and beta1,4-galactosyltransferase 1.

Novel chimeric lacdiNAc (GalNAc(beta1-4)GlcNAc) synthase (c-LacdiNAcS) was generated by gene fusion of alpha-lactalbumin (alpha-LA) and beta1,4-galactosyltransferase 1 (beta1,4-GalT1). c-LacdiNAcS was expressed in Lec8 Chinese hamster ovary (Lec8 CHO) cells and exhibited N-acetylgalactosaminyltransferase (GalNAcT) activity in the absence of exogenous alpha-LA as well as other glycosyltransferase activities including lactose synthase (LacS), and beta1,4-GalT. These glycosyltransferase activities of c-LacdiNAcS were compared to those activities induced in LacS system under the co-presence of bovine beta1,4-GalT1 and alpha-LA, indicating that each domain of alpha-LA and beta1,4-GalT1 on c-LacdiNAcS is not only folding correctly, but also interacting together. Furthermore, c-LacdiNAcS was found to be auto-lacdiNAcylated and can synthesize lacdiNAc structures on cellular glycoproteins, demonstrating that GalNAcT activity of c-LacdiNAcS is functional in Lec8 CHO cells.

Sp1 modulates ncOGT activity to alter target recognition and enhanced thermotolerance in E. coli.

cDNAs encoding three isoforms of OGT (ncOGT, mOGT, and sOGT) were expressed in Escherichia coli in which the coexpression system of OGT with target substrates was established in vivo. No endogenous bacterial proteins were significantly O-GlcNAcylated by any type of OGT isoform while co-expressed p62 and Sp1 were strongly O-GlcNAcylated by ncOGT. These results suggest that most of bacterial proteins appear not to be recognized as right substrates by mammalian OGT whereas cytosolic environments may supply UDP-GlcNAc enough to proceed to O-GlcNAcylation in E. coli. Under these conditions, sOGT was auto-O-GlcNAcylated whereas ncOGT and mOGT were not. Importantly, we found that when Sp1 was coexpressed, ncOGT can O-GlcNAcylate not only Sp1 but also many bacterial proteins. Our findings suggest that Sp1 may modulate the capability of target recognition of ncOGT by which ncOGT can be led to newly recognize bacterial proteins as target substrates, finally generating the O-glyco-bacteria. Our results demonstrate that the O-glyco-bacteria showed enhanced thermal resistance to allow cell survival at a temperature as high as 52 degrees C.

Valproic acid-mediated transcriptional regulation of human GM3 synthase (hST3Gal V) in SK-N-BE(2)-C human neuroblastoma cells.

AIM: To investigate whether valproic acid (VPA) modulates human GM3 synthase (hST3Gal V) mRNA expression, as a part of ganglioside GM3 biosynthesis, in human neuroblastoma cells. METHODS: Using RT-PCR and immunofluorescent confocal microscopy, we examined hST3Gal V mRNA and GM3 levels during VPA-induced differentiation of human neuroblastoma SK-N-BE(2)-C cells. We characterized the VPA-inducible promoter region within the hST3- Gal V gene using luciferase constructs carrying 5'-deletions of the hST3Gal V promoter. RESULTS: RT-PCR indicated that VPA-mediated hST3Gal V induction is transcriptionally regulated. Functional analysis of the 5'-flanking region of the hST3Gal V gene demonstrated that the -177 to -83 region, which contains a cAMP-responsive element (CRE) at -143, functions as the VPA-inducible promoter by actively binding CRE binding protein (CREB). In addition, sitedirected mutagenesis and electrophoretic mobility shift assay indicated that the CRE at -143 is crucial for the VPA-induced expression of hST3Gal V in SK-NBE( 2)-C cells. CONCLUSION: Our results isolated the core promoter region in the hST3Gal V promoter, a CRE at -143, and demonstrated that it is essential for transcriptional activation of hST3Gal V in VPA-induced SK-N-BE(2)-C cells. Subsequent CREB binding to this CRE mediates VPA-dependent upregulation of hST3Gal V gene expression.

Increased alpha2,3-sialylation and hyperglycosylation of N-glycans in embryonic rat cortical neurons during camptothecin-induced apoptosis.

Alterations in the glycan chains of cell surface glycoconjugates are frequently involved biological processes such as cell-cell interaction, cell migration, differentiation and development. Cultured embryonic (E18) rat cortical neurons underwent apoptosis in response to camptothecin, and lectin histochemistry showed that binding to apoptotic neurons of FITC-conjugated Maackia amurensis agglutinin (MAA), which is specific for terminal alpha2,3-sialic acid residues, increased progressively with increasing concentrations of camptothecin. Analysis of the total proteins of apoptotic neurons by SDS-PAGE, and lectin blotting using HRP-labeled MAA, revealed that the expression of terminal alpha2,3-sialic acid residues on an unknown protein with an apparent molecular mass of 25.6 kDa also increased in apoptotic neurons. NP-HPLC analysis of the total cellular N-glycans of normal and apoptotic neurons demonstrated that the expression of structurally simpler biantennary types of N-glycans fell by 49% during apoptosis whereas the more branched triantennary types of N-glycans with terminal sialic acid residues increased by up to 59%. These results suggest that increased surface expression of alpha2,3-sialic acid residues and hyperglycosylation of N-glycans is a common feature of cellular responses to changes in cell physiology such as tumorigenesis and apoptosis.

Bi-functional activities of chimeric lysozymes constructed by domain swapping between bacteriophage T7 and K11 lysozymes.

The lysozymes encoded by bacteriophage T7 and K11 are both bifunctional enzymes sharing an extensive sequence homology (75%). The constructions of chimeric lysozymes were carried out by swapping the N-terminal and C-terminal domains between phage T7 and K11 lysozymes. This technique generated two chimeras, T7K11-lysozyme (N-terminal T7 domain and C-terminal K11 domain) and K11T7-lysozyme (N-terminal K11 domain and C-terminal T7 domain), which are both enzymatically active. The amidase activity of T7K11-lysozyme is comparable with the parental enzymes while K11T7-lysozyme exhibits an activity that is approximately 45% greater than the wild-type lysozymes. Moreover, these chimeric constructs have optimum pH of 7.2-7.4 similar to the parental lysozymes but exhibit greater thermal stabilities. On the other hand, the chimeras inhibit transcription comparable with the parental lysozymes depending on the source of their N-terminals. Taken together, our results indicated that domain swapping technique localizes the N-terminal region as the domain responsible for the transcription inhibition specificity of the wild type T7 and K11 lysozymes. Furthermore, we were able to develop a simple and rapid purification scheme in purifying both the wild-type and chimeric lysozymes.

Differential expression of gangliosides in the ovary and uterus of streptozotocin-induced and db/db diabetic mice.

Gangliosides are widely distributed in mammalian cells and play important roles in various functions such as cell differentiation and growth control. In addition, diabetes and obesity cause abnormal development of reproductive processes in a variety of species. However, the mechanisms underlying these effects, and how they are related, are not fully understood. This study examined whether the differential expression of gangliosides is implicated in the abnormal follicular development and uterine architecture of streptozotocin (STZ)-induced and db/db diabetic mice. Based upon the mobility on high-performance thin-layer chromatography, mouse ovary consisted of at least five different ganglioside components, mainly gangliosides GM3, GM1, GD1a and GT1b, and diabetic ovary exhibited a significant reduction in ganglioside expression with apparent changes in the major gangliosides. A prominent immunofluorescence microscopy showed a dramatic loss of ganglioside GD1a expression in the primary, secondary and Graafian follicles of STZ-induced and db/db diabetic mice. A significant decrease in ganglioside GD3 expression was also observed in the ovary of db/db mice. In the uterus of STZ-induced diabetic mice, expression of gangliosides GD1a and GT1b was obviously reduced, but gangliosides GM1, GM2 and GD3 expression was increased. In contrast, the uterus of db/db mice showed a significant increase in gangliosides GM1, GD1a and GD3 expression. Taken together, a complex pattern of ganglioside expression was seen in the ovary and uterus of normoglycemic ICR and db/+ mice, and the correspoding tissues in diabetic mice are characterized by appreciable changes of the major ganglioside expression. These results suggest that alterations in ganglioside expression caused by diabetes mellitus may be implicated in abnormal ovarian development and uterine structure.

Pathophysiological implication of ganglioside GM3 in early mouse embryonic development through apoptosis.

Apoptosis may occur in early embryos where the execution of essential developmental events has failed, and gangliosides, sialic acid-conjugated glycosphingolipids, are proposed to regulate cell differentiation and growth. To evaluate the regulatory roles of ganglioside GM3 in early embryonic development, this study examined its expressional patterns in apoptotic cells during early embryonic development in mice. Pre-implanted embryos were obtained by in vitro fertilization, which were treated at the 4-cell stage with three the apoptosis inducers, actinomycin D, camptothecin and cycloheximide, for 15 h. All three inducers significantly increased the percentage of apoptotic cells, as measured using a TUNEL method, but remarkably reduced the total cell numbers. The numbers of morula and blastocyst stages were significantly decreased by treatment of the embryos with the three apoptosis inducers compared with the control, with a similar result also observed in the number of blastomeres. Staining of early embryos with Hoechst 33342 revealed a significant percentage of apoptotic nuclei. Prominent immunofluorescence microscopy revealed a significant difference in the ganglioside GM3 expression in apoptotic embryos compared with the control, and RT-PCR also demonstrated a dramatic increase in ganglioside GM3 synthase mRNA in the apoptotic embryos. These results suggest that ganglioside GM3 may be pathophysiologically implicated in the regulation of early embryonic development through an apoptotic mechanism.

A mutagenic study of beta-1,4-galactosyltransferases from Neisseria meningitidis.

N-terminal His-tagged recombinant beta-1,4-galactosyltransferase from Neisseria meningitidis was expressed and purified to homogeneity by column chromatography using Ni-NTA resin. Mutations were introduced to investigate the roles of, Ser68, His69, Glu88, Asp90, and Tyr156, which are components of a highly conserved region in recombinant beta-1,4 galactosyltransferase. Also, the functions of three other cysteine residues, Cys65, Cys139, and Cys205, were investigated using site-directed mutagenesis to determine the location of the disulfide bond and the role of the sulfhydryl groups. Purified mutant galactosyltransferases, His69Phe, Glu88Gln and Asp90Asn completely shut down wild-type galactosyltransferase activity (1-3 %). Also, Ser68Ala showed much lower activity than wild-type galactosyltransferase (19 %). However, only the substitution of Tyr156Phe resulted in a slight reduction in galactosyltransferase activity (90 %). The enzyme was found to remain active when the cysteine residues at positions 139 and 205 were replaced separately with serine. However, enzyme reactivity was found to be markedly reduced when Cys65 was replaced with serine (27 %). These results indicate that conserved amino acids such as Cys65, Ser68, His69, Glu88, and Asp90 may be involved in the binding of substrates or in the catalysis of the galactosyltransferase reaction.

Expression and characterization of beta-1,4-galactosyltransferase from Neisseria meningitidis and Neisseria gonorrhoeae.

The lgtB genes that encode beta-1,4-galactosyltransferases from Neisseria meningitidis ATCC 13102 and gonorrhoeae ATCC 31151 were isolated by a polymerase chain reaction using the pfu DNA polymerase. They were expressed under the control of lac and T7 promoters in Escherichia coli M15 and BL21 (DE3). Although the genes were efficiently expressed in E. coli M15 at 37 degrees C (33 kDa), most of the beta-1,4-galactosyltransferases that were produced were insoluble and proteolysed into enzymatically inactive polypeptides that lacked C-terminal residues (29.5 kDa and 28 kDa) during the purification steps. When the temperature of the cell growth was lowered to 25 degrees C, however, the solubility of the beta-1,4-galactosyltransferases increased substantially. A stable N-terminal his-tagged recombinant enzyme preparation could be achieved with E. coli BL21 (DE3) that expressed lgtB. Therefore, the cloned beta-1,4-galactosyltransferases were expressed under the control of the T7 promoter in E. coli BL21 (DE3), mostly to the soluble form at 25 degrees C. The proteins were easily purified to homogeneity by column chromatography using Ni-NTA resin, and were found to be active. The galactosyltransferases exhibited pH optimum at 6.5-7.0, and had an essential requirement for the Mn(+2) ions for its action. The Mg(+2) and Ca(+2) ions showed about half of the galactosyltransferase activities with the Mn(+2) ion. In the presence of the Fe(+2) ion, partial activation was observed with the beta-1,4-galactosyltransferase from N. meningitidis (64% of the enzyme activity with the Mn(+2) ion), but not from N. gonorrhoeae. On the other hand, the N(+2), Zn(+2), and Cu(+2) ions could not activate the beta-1,4- galactosyltransferase activity. The inhibited enzyme activity with the Ni(+2) ion was partially recovered with the Mn(+2) ion, but in the presence of the Fe(+2), Zn(+2), and Cu(+2) ions, the Mn(+2) ion could not activate the enzyme activities. Also, the beta-1,4-galactosyltransferase activity was 1.5-fold stimulated with the non-ionic detergent Triton X-100 (0.1-5 percent).

Neuroprotective effects of black soybean anthocyanins via inactivation of ASK1-JNK/p38 pathways and mobilization of cellular sialic acids.

AIMS: To investigate neuroprotective effects of three major anthocyanins (cyanidin-3-O-glucoside, delphinidin-3-O-glucoside, and petunidin-3-O-glucoside) isolated from the black soybean (Glycine max L.) cv. Cheongja 3 seed coat against H(2)O(2)-induced cell death of human brain neuroblastoma SK-N-SH cells. MAIN METHODS: Cell viability, reactive oxygen species (ROS) generation, production and expression of heme oxygenase (HO)-1 and inactivation of mitogen-activated protein (MAP) kinase cascades were determined by MTT assay, 2,7-dichlorofluorescein diacetate (DCF-DA) assay, reverse transcriptase polymerase chain reaction (RT-PCR), and western blotting, respectively. KEY FINDINGS: Pretreatment with anthocyanins reduced the cytotoxicity of H(2)O(2) on SK-N-SH cells, dose-dependently reduced the intracellular ROS level and inactivated apoptosis signal-regulating kinase (ASK1, Thr845), p38, and c-Jun N-terminal kinase (JNK) proteins. The HO-1 and Neu1 mRNA levels were increased by H(2)O(2) (25 µM) and further elevated by the pretreatment with anthocyanins. Sialic acids added to the culture plates not only attenuated the cytotoxicity of H(2)O(2) (25 µM) but also reduced intracellular ROS level. These results suggest that Cheongja 3 black soybean seed coat anthocyanins have brain neuroprotective effects against oxidative stress (H(2)O(2)) by inhibiting the activation of ASK1-JNK/p38 pathways, scavenging ROS, stimulating the expression of HO-1 and, more interestingly, recruiting cellular free sialic acids through up-regulation of Neu1 sialidase gene expression. SIGNIFICANCE: This is the first report indicating potent health benefits of black soybean seed coat anthocyanins in neuroprotection by triggering mobilization of cellular free sialic acid and utilizing it as an additional biological antioxidant in brain neural cells.

Triptolide downregulates human GD3 synthase (hST8Sia I) gene expression in SK-MEL-2 human melanoma cells.

In this study, we have shown that gene expression of human GD3 synthase (hST8Sia I) is suppressed by triptolide (TPL) in human melanoma SK-MEL-2 cells. To elucidate the mechanism underlying the downregulation of hST8Sia I gene expression in TPL-treated SK-MEL-2 cells, we characterized the TPL-inducible promoter region within the hST8Sia I gene using luciferase constructs carrying 5'-deletions of the hST8Sia I promoter. Functional analysis of the 5'-flanking region of the hST8Sia I gene demonstrated that the -1146 to -646 region, which contains putative binding sites for transcription factors c-Ets-1, CREB, AP-1 and NF-κB, functions as the TPL-inducible promoter of hST8Sia I in SK-MEL-2 cells. Site-directed mutagenesis and ChIP analysis indicated that the NF-κB binding site at -731 to -722 is crucial for TPL-induced suppression of hST8Sia I in SK-MEL-2 cells. This suggests that TPL induces down-regulation of hST8Sia I gene expression through NF-κB activation in human melanoma cells.

Effects of daunorubicin on ganglioside expression and neuronal differentiation of mouse embryonic stem cells.

Gangliosides are implicated in neuronal development processes. The regulation of ganglioside levels is closely related to the induction of neuronal cell differentiation. In this study, the relationship between ganglioside expression and neuronal cell development was investigated using an in vitro model of neural differentiation from mouse embryonic stem (mES) cells. Daunorubicin (DNR) was applied to induce the expression of gangliosides in embryoid body (EB) (4+). We observed an increase in expression of gangliosides in all stages of EBs by treatment of DNR (2microM). High-performance thin-layer chromatography (HPTLC) showed that gangliosides GD3, GD1a, GT1b, and GQ1b increased in DNR-treated 7-day-old EB (4+) [EB (4+):7]. DNR treatment significantly increased the expression of gangliosides, especially GT1b and GQ1b in comparison to control cells. Interestingly, GQ1b co-localized with microtubule-associated protein 2 (MAP-2) expressing cells in DNR-treated EB (4+):7. The co-localization of GQ1b and MAP-2 was found in neurite-bearing cells in DNR-treated 15-day-old EB (4+) [EB (4+):15], whereas no significant expression of GQ1b and less neurite formation were observed in untreated control. Also, the expression of synaptophysin and NF200, both neuronal markers associated with neruites, was increased by DNR treatment. These results demonstrate that DNR increases expression of gangliosides, especially GQ1b, in differentiating neuronal cells. Further, neurite-bearing neuronal cell differentiation can be facilitated by DNR, possibly through the induction of gangliosides. Thus, the present data suggest that DNR is beneficial for facilitating neuronal differentiation from ES cells and among the gangliosides analyzed in the present study, GQ1b is mainly involved in neurite formation.

Transcriptional regulation and O-GlcNAcylation activity of zebrafish OGT during embryogenesis.

Zebrafish OGT (zOGT) sequence was identified in zebrafish (Danio rerio) genome and six different transcriptional variants of zOGT, designated var1 to var6, were isolated. Here we describe the developmental regulation of zOGT variants at transcriptional level and characterization of their OGT activities of protein O-GlcNAcylation. OGT transcriptional variants in zebrafish were differentially generated by alternative splicing and in particular, var1 and var2 were contained by 48 bp intron as a novel exon sequence, demonstrating that this form of OGT was not found in mammals. Transcript analysis revealed that var1 and var2 were highly expressed at early phase of development including unfertilized egg until dome stage whereas var3 and var4 were begins to be expressed at sphere stage until late phase of development. Our data indicate that var1 and var2 are likely to be maternal transcripts. The protein expression assay in Escherichia coli-p62 system showed that OGT activities of var3 and var4 were found to be only active whereas those of other variants were inactive.

OGT functions as a catalytic chaperone under heat stress response: a unique defense role of OGT in hyperthermia.

Protein O-GlcNAcylation is proceeded by O-linked GlcNAc transferase (OGT) in nucleocytoplasm and is involved in many biological processes although its physiological role is not clearly defined. To identify the functional significance of O-GlcNAcylation, we investigated heat stress effects on protein O-GlcNAcylation. Here, we found that protein O-GlcNAcylation was significantly increased in vivo during acute heat stress in mammalian cells and simultaneously, the enhanced protein O-GlcNAcylation was closely associated with cell survival in hyperthermia. Our results demonstrate that hyperthermal cytotoxicity may considerably be facilitated under the condition of insufficient level of protein O-GlcNAcylation inside cells. Furthermore, OGT reaction might be crucial for triggering thermotolerance to recover hyperthermal sensitivity without particular induction of heat shock proteins (hsps). Thus, we propose that OGT can respond rapidly to heat stress through the enhancement of nucleocytoplasmic protein O-GlcNAcylation for a rescue from the early phase of hyperthermal cytotoxicity.

High-level expression of human glycosyltransferases in insect cells as biochemically active form.

cDNAs, encoding human beta1,4-galactosyltransferase (hGalT I, EC 2.4.1.22), human Galbeta1,3(4)-GlcNAc alpha2,3-sialyltransferase (hST3GalIII, EC 2.4.99), and human Galbeta1,4-GlcNAc alpha2,6-sialyltransferase (hST6Gal I, EC 2.4.99.1), were cloned from human cell lines. In order to express these glycosyltransferases as secreted form in insect cells, cDNAs were inserted into a novel baculovirus transfer vector equipped with the mouse IgM signal peptide and IgG binding domain of the Staphylococcus aureus protein A as an N-terminal fusion partner. About 14 mg hGalT I, 8 mg hST3GalIII, and 6.4 mg hST6Gal I were purified from 1 liter of recombinant baculovirus infected insect cell culture media. The specific activities of recombinant hGalT I and hST6Gal I were determined as 0.65 and 1.6 U/mg protein, respectively. These results indicated that the recombinant hGalT I and hST6Gal I retained enzyme activities at similar level to those of the authentic one although they were fused with the IgG binding domain at the N-terminus. Taken together, the mouse IgM signal peptide and IgG binding domain of the protein A could be efficiently used as an N-terminus fusion partner for the over-expression of heterologous proteins in insect cells.

The Hexapeptide inhibitor of Galbeta 1,3GalNAc-specific alpha 2,3-sialyltransferase as a generic inhibitor of sialyltransferases.

The mammalian Galbeta1,3GalNAc-specific alpha2,3-sialyltransferase (ST3Gal I) was expressed as a secreted glycoprotein in High Five (Trichoplusia ni) cells. Using this recombinant ST3Gal I, we screened the synthetic hexapeptide combinatorial library to explore a sialyltransferase inhibitor. We found that the hexapeptide, NH(2)-GNWWWW, exhibited the most strong inhibition of ST3Gal I among five different hexapeptides that were finally selected. The kinetic analysis of ST3Gal I inhibition demonstrated that this hexapeptide could act as a competitive inhibitor (K(i) = 1.1 microm) on CMP-NeuAc binding to the enzyme. Moreover, the hexapeptide was shown to strongly inhibit both N-glycan-specific alpha2,3- and alpha2,6-sialyltranferase in vitro, suggesting that this peptide may inhibit the broad range of sialyltransferases regardless of their linkage specificity. The inhibitory activity in vivo was investigated by RCA-I lectin blot analyses and by metabolic d-[6-(3)H]GlcNH(2) radiolabeling analyses of N- and O-linked oligosaccharides in Chines hamster ovary cells. Our results demonstrate that the hexapeptide can act as a generic inhibitor of the N- and O-glycan-specific sialyltransferases in mammalian cells, which results in the significantly reduced NeuAc expression on cellular glycoproteins in vivo.