Alteration in N-acetylglucosaminyltransferase activities and glycan structure in tissue and bile glycoproteins from extrahepatic bile duct carcinoma

The activities of three N-acetylglucosaminyltransferases (GnT)-III, IV and V, as well as the structural alterations of N-glycans on the glycoproteins in cancer tissues and bile specimens from 28 cases of extrahepatic bile duct carcinoma (EBDC) were compared with those from 18 cases of benign biliary duct diseases (BBDD). GnT activities were determined with fluorescence-labeled substrate using a HPLC method. It was found that GnT-III and GnT-V activities in EBDC were increased to 3.14 and 15.96 times respectively of the mean BBDD values, but GnT-IV remained unchanged. The activity of GnT-V was correlated with the grade of differentiation and TMN stage of EBDC. The up-regulation of GnT-III resulted in the increased bisecting-GlcNAc on the N-glycans of glycoproteins in cancer tissues and a 201 kDa bile glycoprotein when analyzed with HRP-labeled E₄-PHA. The increased GnT-V activity led to the elevation of the β1,6GlcNAc branch (or antennary number) on the N-glycans in cancer tissue glycoproteins and 201, 163, 122 kDa proteins in the bile as probed with HRP-labeled DSA. These findings suggest that the alteration in GnT activities may be involved in the malignant transformation and development of EBDC, resulting in the aberrant glycosylation of some tissue and bile proteins. The latter was expected to be used in the clinical diagnosis and prognosis evaluation in EBDC patients. Published in 2004. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthetic substrate analogues for UDP-GlcNAc: Manα1-6R β(1-2)-N-acetylglucosaminyltransferase II. Substrate specificity and inhibitors for the enzyme

UDP-GlcNAc: Man1-6R (1-2)-N-acetylglucosaminyltransferase II (GlcNAc-T II; EC 2.4.1.143) is a key enzyme in the synthesis of complexN-glycans. We have tested a series of synthetic analogues of the substrate Man1-6(GlcNAc1-2Man1-3)Man-O-octyl as substrates and inhibitors for rat liver GlcNAc-T II. The enzyme attachesN-acetylglucosamine in 1-2 linkage to the 2-OH of the Man1-6 residue. The 2-deoxy analogue is a competitive inhibitor (K _i=0.13mm). The 2-O-methyl compound does not bind to the enzyme presumably due to steric hindrance. The 3-, 4- and 6-OH groups are not essential for binding or catalysis since the 3-, 4- and 6-deoxy and -O-methyl derivatives are all good substrates. Increasing the size of the substituent at the 3-position to pentyl and substituted pentyl groups causes competitive inhibition (K _i=1.0–2.5mm). We have taken advantage of this effect to synthesize two potentially irreversible GlcNAc-T II inhibitors containing a photolabile 3-O-(4,4-azo)pentyl group and a 3-O-(5-iodoacetamido)pentyl group respectively. The data indicate that none of the hydroxyls of the Man1-6 residue are essential for binding although the 2- and 3-OH face the catalytic site of the enzyme. The 4-OH group of the Man-O-octyl residue is not essential for binding or catalysis since the 4-deoxy derivative is a good substrate; the 4-O-methyl derivative does not bind. This contrasts with GlcNAc-T I which cannot bind to the 4-deoxy-Man- substrate analogue. The data are compatible with our previous observations that a bisectingN-acetylglucosamine at the 4-OH position prevents both GlcNAc-T I and GlcNAc-T II catalysis. However, in the case of GlcNAc-T II, the bisectingN-acetylglucosamine prevents binding due to steric hindrance rather than to removal of an essential OH group. The 3-OH of the Man1-3 is an essential group for GlcNAc-T II since the 3-deoxy derivative does not bind to the enzyme. The trisaccharide GlcNAc1-2Man1-3Man-O-octyl is a good inhibitor (K _i=0.9mm). The above data together with previous studies indicate that binding of the GlcNAc1-2Man1-3Man- arm of the branched substrate to the enzyme is essential for catalysis. Abbreviations: GlcNAc-T I, UDP-GlcNAc:Man1-3R (1-2)-N-acetylglucosaminyltransferase I (EC 2.4.1.101); GlcNAc-T II, UDP-GlcNAc:Man1-6R (1-2)-N-acetylglucosaminyltransferase II (EC 2.4.1.143); MES, 2-(N-morpholino)ethane sulfonic acid monohydrate.     

Core 2N-acetylglucosaminyltransferase activity: a diagnostic marker for Wiskott-Aldrich syndrome

Serine/threonine (O)-linked oligosaccharide on cell-surface CD43 has been reported to be abnormal in haemopoietic lineages of patients with the X-linked immunodeficiency, Wiskott-Aldrich syndrome (WAS). This defect largely appears to be the result of abnormal regulation of UDP-GlcNAc:Gal1-3GalNAc-R1-6-N-acetylglucosaminyltransferase (also known as core 2 GlcNAc-T), an enzyme in the Golgi apparatus that is subject to regulation during haemopoietic differentiation. To determine whether core 2 GlcNAc-T activity provides a reliable marker for WAS, we studied 12 unrelated WAS patients with respect to their expression of this enzyme activity. Compared with healthy subjects, the WAS patients showed levels of core 2 activity that were, on average, 2.5- and 3.9-fold higher in fresh lymphocytes and platelets respectively. These data suggest that altered core 2 GlcNAc-T activity is consistently found in lymphocytes and platelets of WAS patients and as such may provide a diagnostic marker for the disease. In view of the relatively limited amounts of blood sample generally available from infants and young children, we have also tested a more sensitive coupled assay that permits assessment of core 2 GlcNAc-T activity in very small samples of cells and which would therefore render this assay of wide clinical applicability.     

Effects of dibutyryl cAMP and bromodeoxyuridine on expression ofN-acetylglucosaminyltransferases III and V in GOTO neuroblastoma cells

The sugar chain structures of the cell surface change dramatically during cellular differentiation. A human neuroblastoma cell line, GOTO, is known to differentiate into neuronal cells and Schwannian cell-like cells on treatments with dibutyryl cAMP and bromodeoxyuridine, respectively. We have examined the expression of UDP-N-acetylglucosamine: -d-mannoside -1,4N-acetylglucosaminyltransferase III (GnT-III: EC 2.4.1.144) and UDP-N-acetylglucosamine: -6-d-mannoside -1,6N-acetylglucosaminyltransferase V (GnT-V: EC 2.4.1.155), two major branch forming enzymes inN-glycan synthesis, in GOTO cells on two distinct directions of differentiation.In neuronal cell differentiation, GnT-III activity showed a slight increase during initial treatment with Bt₂cAMP for 4 days and decreased drastically after the fourth day, but the mRNA level of GnT-III did not show a decrease but in fact a slight increase. GnT-V activity increased to approximately two- to three-fold the initial level with increasing mRNA level after 8 days, and lectin blot analysis showed an increase in reactivity toDatsura stramonium (DSA) of the immunoprecipitated neural cell adhesion molecule (NCAM). In Schwannian cell differentiation, the activity and mRNA level of GnT-III showed no significant change on treatment with BrdU. GnT-V activity also showed no change in spite of the gradual increase in the mRNA level. These results suggest that the activation of GnT-V during neuronal cell differentiation of GOTO cells might be a specific change for branch formation in N-glycans, and this affects the sugar chain structures of some glycoproteins such as NCAM.Abbreviations and trivial names GnT N-acetylglucosaminyltransferase - Bt₂cAMP N ⁶,O ⁶-dibutyryl cAMP - BrdU bromodeoxyuridine - DSA Datsura stramonium - NCAM neural cell adhesion molecule - PAGE polyacrylamide gel electrophoresis     

Molecular cloning of cDNA encoding N-acetylglucosaminyltransferase II from Arabidopsis thaliana

N-acetylglucosaminyltransferase II (GnTII, EC 2.4.1.143) is a Golgi enzyme involved in the biosynthesis of glycoprotein-bound N-linked oligosaccharides, catalysing an essential step in the conversion of oligomannose-type to complex N-glycans. GnTII activity has been detected in both animals and plants. However, while cDNAs encoding the enzyme have already been cloned from several mammalian sources no GnTII homologue has been cloned from plants so far. Here we report the molecular cloning of an Arabidopsis thalianaGnTII cDNA with striking homology to its animal counterparts. The predicted domain structure of A. thalianaGnTII indicates a type II transmembrane protein topology as it has been established for the mammalian variants of the enzyme. Upon expression of A. thalianaGnTII cDNA in the baculovirus/insect cell system, a recombinant protein was produced that exhibited GnTII activity.     

Aspergillus melleus protease-catalyzed peptide synthesis using the carbamoylmethyl ester as an acyl donor in 1,1,1,3,3,3-hexafluoro- 2-propanol/N,N-dimethylformamide

The coupling between the carbamoylmethyl ester of an N-protected amino acid or dipeptide (at 25 mM) and an amino acid amide (at 100 mM) was achieved using Aspergillus melleus protease in 1,1,1,3,3,3-hexafluoro-2-propanol/N,N-dimethylformamide (1:1, v/v); the coupling efficiencies were dependent largely on the combination of amino acid residues: e.g. the dipeptide yields after 48 h were for l-Ala + Gly, 100% and for l-Leu + l-Leu, 16%.