An alpha-L-fucosidase from Penicillium multicolor as a candidate enzyme for the synthesis of alpha (1-->3)-linked fucosyl oligosaccharides by transglycosylation

A new alpha-L-fucosidase was partially purified from the culture broth of Penicillium multicolor, which was available commercially as a freeze dried powder by the name of Lactase-P. This enzyme catalysed the transglycosylation of fucose residue of p-nitrophenyl-alpha-L-fucopyranoside to give alpha-L-Fuc-(1-->3)-D-Glc or alpha-L-Fuc-(1-->3)-D-GlcNAc regioselectively. This enzyme was more stable in the organic co-solvents than the alpha-fucosidase from Aspergillus niger, which was also proposed previously by us as an enzyme to produce fucosyl oligosaccharides.

Effect of Leuconostoc mesenteroides NRRL B-512F dextransucrase carboxy-terminal deletions on dextran and oligosaccharide synthesis

Dextransucrase (DSR-S) from Leuconostoc mesenteroides NRRL B-512F is a glucosyltransferase that catalyzes synthesis of soluble dextran from sucrose. In the presence of efficient acceptor molecules, such as maltose, the reaction pathway is shifted toward glucooligosaccharide synthesis. Like glucosyltransferases from oral streptococci, DSR-S possesses a C-terminal glucan-binding domain composed of a series of tandem repeats. In order to determine the role of the C-terminal region of DSR-S in dextran or oligosaccharide synthesis, four DSR-S genes with deletions at the 3' end were constructed. The results showed that the C-terminal region modulated the initial velocity of dextran synthesis but that the K(m) for sucrose, the optimum pH, and the activation energy were all unaffected by the deletions. The C-terminal domain modulated the rate of oligosaccharide synthesis whatever acceptor molecule was used (a good acceptor molecule such as maltose or a poor acceptor molecule such as fructose). The C-terminal domain seemed to play no role in the catalytic process in dextran and oligosaccharide synthesis. In fact, it seems that the role of the C-terminal domain of DSR-S may be to facilitate the translation of dextran and oligosaccharides from the catalytic site.

Transcriptional and posttranscriptional regulation of alpha 1,3-galactosyltransferase in activated endothelial cells results in decreased expression of Gal alpha 1,3Gal

Gal alpha 1,3Gal carbohydrate residues are present in the glycoproteins and glycolipids of lower mammals, and appear to be involved in the binding specificity of several membrane receptors. We report here that endothelial cells stimulated with lipopolysaccharide or inflammatory cytokines modulate their expression of UPD-Gal: beta-D-Gal alpha 1,3-galactosyltransferase (alpha 1,3GT), the Golgi enzyme that attaches a galactose in alpha 1,3 configuration to an N-acetyllactosamine acceptor. Upon activation, the steady state level of mRNA is transiently increased, the modifications being paralleled by a transcriptional regulation of the gene. Cell-associated enzyme activity, on the other hand, falls rapidly after activation, before being up- and downregulated with kinetics that parallel those of the mRNA, and after 3 days reaches a level representing 40-60% of the activity in cells before activation. Overall Gal alpha 1,3Gal expression at the cell surface follows enzyme activity, except that it is insensitive to the rapid and transient reduction of activity occurring shortly after activation. This reduced alpha 1,3GT activity in stimulated EC is correlated with lower stability of the protein, and with a switch in the expression of the isoform pattern, isoform 1 being predominant in resting cells whereas after activation it is isoform 2 that predominates. The two isoforms, however, appear to have similar intrinsic stability, so that the reduced stability of the enzyme in activated EC probably results from an induced proteolytic degradation pathway.

Galactosylononitol and stachyose synthesis in seeds of adzuki bean. Purification and characterization of stachyose synthase

Stachyose synthase (STS) (EC 2.4.1.67) was purified to homogeneity from mature seeds of adzuki bean (Vigna angularis). Electrophoresis under denaturing conditions revealed a single polypeptide of 90 kD. Size-exclusion chromatography of the purified enzyme yielded two activity peaks with apparent molecular masses of 110 and 283 kD. By isoelectric focusing and chromatofocusing the protein was separated into several active forms with isoelectric point values between pH 4. 7 and 5.0. Purified STS catalyzed the transfer of the galactosyl group from galactinol to raffinose and myo-inositol. Additionally, the enzyme catalyzed the galactinol-dependent synthesis of galactosylononitol from D-ononitol. The synthesis of a galactosylcyclitol by STS is a new oberservation. Mutual competitive inhibition was observed when the enzyme was incubated with both substrates (raffinose and ononitol) simultaneously. Galactosylononitol could also substitute for galactinol in the synthesis of stachyose from raffinose. Although galactosylononitol was the less-efficient donor, the Michaelis constant value for raffinose was lower in the presence of galactosylononitol (13.2 mm) compared with that obtained in the presence of galactinol (38.6 mm). Our results indicate that STS catalyzes the biosynthesis of galactosylononitol, but may also mediate a redistribution of galactosyl residues from galactosylononitol to stachyose.

Enzymatic synthesis of oligosaccharides containing Gal beta-->4Gal disaccharide at the non-reducing end using beta-galactanase from Penicillium citrinum

The transglycosylation reaction was done with a beta-galactanase from Penicillium citrinum. The regioselectivity in the transglycosylation reaction was studied using soy bean arabinogalactan as a donor and mono- or disaccharide derivatives containing beta-galactosyl residue as acceptors. We also synthesized oligosaccharides containing Gal beta 1-->4Gal sequence such as Gal beta 1-->4Gal beta1-->4Glc, Gal beta 1-->4Gal beta 1-->3GlcNac, Gal beta 1-->4Gal beta 1-->4GlcNAc, Gal beta 1-->4Gal beta 1-->6GlcNAc, and Gal beta 1-->4Gal beta 1-->3GalNAc for use in the total synthesis of complex sugar chains.

Structural analysis of disaccharides synthesized by beta-D-glucosidase of Bifidobacterium breve clb and their assimilation by Bifidobacteria

Circulation of a solution of 1 M D-fucose and 1 M D-glucose through a reaction system consisting of serial columns of immobilized recombinant beta-D-glucosidase of Bifidobacterium breve clb and activated charcoal gave two oligosaccharides. Structural analysis identified these oligosaccharides as D-fucosylglucose (6-O-beta-D-Fucopyranosyl-D-glucose) and gentiobiose (6-O-beta-D-Glucopyranosyl-D-glucose). The D-fucosylglucose obtained was well assimilated by many Bifidobacteria but not by the other intestinal bacteria tested.

All-aqueous, regiospecific transglycosylation synthesis of 3-O-alpha-L-fucopyranosyl-2-acetamido-2-deoxy-D-glucopyranose, a building block for the synthesis of branched oligosaccharides

A transglycosylation reaction, carried out in an aqueous medium and catalyzed by a crude preparation of alpha-fucosidase (E.C. 3.2.1.51) from Aspergillus niger, allowed for the regiospecific synthesis of the disaccharide 3-O-alpha-L-fucopyranosyl-2-acetamido-2-deoxy-D-glucopyranose using p-nitrophenyl-alpha-L-fucopyranose as the donor and 2-acetamido-2-deoxy-D-glucopyranose as the acceptor. The chemical identity of the product obtained was demonstrated by HPLC, ion spray mass spectrometry and NMR spectroscopy. Further transglycosylation using a beta-galactosidase (E.C. 3.2.1.23) yielded the branched oligosaccharide 2-acetamido-2-deoxy-3-O-(alpha-L-fucopyranosyl)-4-O-(beta-D-galactopyran osyl)-D-glucopyranose, i.e., the Lewis(x) antigen.

Differential expression of LacdiNAc sequences (GalNAc beta 1-4GlcNAc-R) in glycoproteins synthesized by Chinese hamster ovary and human 293 cells

The lacdiNAc sequence GalNAc beta 1-->4GlcNAc beta 1-R occurs in the N- and O-glycans of many glycoproteins in vertebrate and invertebrates. We now report that both human 293 cells and Chinese hamster ovary (CHO) cells contain a UDPGalNAc:GlcNAc beta 1,4 N-acetylgalactosaminyltransferase (beta 1,4GalNAcT) that forms the lacdiNAc sequence. The beta 1,4GalNAcT in CHO cells is distinct from beta 1,4 galactosyltransferase in that the latter enzyme, but not the former, binds to a column of immobilized bovine alpha-lactalbumin. To determine whether endogenous glycoproteins in these cells contain lacdiNAc sequences, glycoproteins from 293 cells, CHO and Lec8 CHO cells were desialylated and passed over immobilized Wisteria floribunda agglutinin (WFA), a plant lectin with affinity for terminal GalNAc residues. WFA bound to approximately 120 and approximately 80 kDa glycoproteins in 293 cells and glycans from these glycoproteins contained lacdiNAc sequences. The approximately 120 kDa glycoproteins in 293 cells bound by WFA is a mixture of both the lysosome-associated membrane glycoproteins LAMPs-1 and -2. WFA bound to two glycoproteins of approximately 47 and approximately 78 kDa in Lec8 CHO cells, but these glycoproteins are not LAMPs and they do not contain the lacdiNAc sequence. Instead, they contain multiple GalNAc alpha-Ser/Thr O-glycans that promote binding to WFA. Thus, the beta 1,4GalNAcT in 293 cells displays a limited specificity in its recognition of acceptors, whereas the beta 1,4GalNAcT in CHO cells fails to promote synthesis of the cognate lacdiNAc sequence. The presence of the beta 1,4GalNAcT may not be sufficient for synthesis of lacdiNAc sequences and other factors may contribute to regulate the functionality of the enzyme.

The synthesis of galactopyranosyl derivatives with beta-galactosidases of different origins

beta-Galactosidases from four different sources were used to catalyze the transfer of beta-D-galactopyranosyl from 4-nitrophenyl-beta-D-galactopyranoside to a hydroxyl group of 2-acetamido-2-deoxy-galactopyranose in the synthesis of Gal beta (1-3)GalNAc (1), Gal beta (1-4)GalNAc (2) and Gal beta (1-6)GalNAc (3), in triethyl phosphate buffered solutions (20-60%). When beta-galactosidases from Penicillium multicolor and Aspergillus oryzae were used as the catalysts, the beta (1-6)-linked disaccharide was produced as the major product. However, with beta-galactosidase from Bifidobacterium bifidum, the major products were the beta (1-4) and beta (1-6)-linked disaccharides. On the other hand, with beta-galactosidase from Streptococcus 6646K, beta (1-3)-linked disaccharide was predominant together with beta (1-4)-linked isomer. Gal beta (1-3)GlcNAc (4), Gal beta (1-4)GlcNAc (5) and Gal beta (1-6)GlcNAc (6) were also synthesized with beta-galactosidase from S. 6646K and B. bifidum with 2-acetamido-2-deoxy-glucopyranose as the acceptor and PNPGal as the donor. In both cases, the beta (1-4)-linked disaccharide was predominantly produced. In addition, a comparative study was carried out to determine the regioselectivity of the transglycosylation reaction as well as the hydrolytic specificity toward the same linked disaccharides.

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.

Acceptor specificity of cyclodextrin glucanotransferase from an alkalophilic Bacillus species and synthesis of glucosyl rhamnose

Cyclodextrin glucanotransferase [1,4-alpha-D-glucan 4-alpha-D-(1,4-alpha-D-glucano)-transferase (cyclizing), EC 2. 4. 1. 19] from an alkalophilic Bacillus species A2-5a had a wider acceptor specificity than that from B. macerans, which was similar to those from B. stearothermophilus and B. circulans. Glucosyl rhamnose produced by the CGTase was identified as glucopyranosyl-alpha-1,4-rhamnopyranose by alpha- and beta-glucosidase treatments, and 1H- and 13C-NMR analyses.

Abnormal expression of galactosyl(alpha 1-->3) galactose epitopes in squamous cells of the uterine cervix infected by human papillomavirus

This study describes the presence of alpha-galactosyl epitopes on 12 cervical biopsy samples with features of human papillomavirus infection (HPV) and different stages of cervical intraepithelial neoplasia. An avidin-biotin-peroxidase assay with a monoclonal antibody recognizing gal(alpha 1-->3)gal residues was strongly positive in 5 of 12 cases. None of the controls stained (p = 0.02). Immunostaining was intense in the areas with the highest viral load (koilocytes and keratinocytes) and absent in malignant foci. Immunostaining was also absent in normal exo- and endocervical epithelium of 12 controls with no features of HPV infection. A faint background staining in cases and controls was evident, but similar. These initial findings suggest that alpha-galactosyl epitopes are expressed in cervical squamous cells infected with HPV, turning them vulnerable to lysis by natural anti-alpha-galactosyl antibodies.

Glycosidase-catalysed oligosaccharide synthesis: preparation of N-acetylchitooligosaccharides using the beta-N-acetylhexosaminidase of Aspergillus oryzae

The beta-N-acetylhexosaminidase of Aspergillus oryzae catalyses the formation of 2-acetamido-4-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-2-deoxy-D- glucopyranose (di-N-acetylchitobiose) and 2-acetamido-6-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-2-deoxy-D- glucopyranose from p-nitrophenyl 2-acetamido-2-deoxy-beta-D-glucopyranoside and 2-acetamido-2-deoxy-D-glucopyranose. The ratio of the two disaccharides is time-dependent. The ratio of (1-->4)- to (1-->6)-isomers is a maximum (approximately 9:1) at the point of disappearance of the glycosyl donor. If left to evolve, the ratio changes to 92:8 in favour of the (1-->6)-isomer. Either the (1-->4)- or the (1-->6)-isomer can be isolated by treating the appropriately enriched dissaccharide mixture with the beta-N-acetylhexosaminidase of Jack bean (Canavalia ensiformis) or the beta-N-acetylhexosaminidase of A. oryzae, respectively. Di-N-acetylchitobiose [GlcNAc(beta 1-4)GlcNAc] is an efficient donor of 2-acetamido-2-deoxy-D-glucopyranosyl units in reactions catalysed by the N-acetylhexosaminidase of A. oryzae. Di-N-acetylchitobiose itself acts as acceptor to give tri-N-acetylchitotriose [GlcNAc(beta 1-4)GlcNAc(beta 1-4)GlcNAc]. As the trisaccharide accumulates it, in turn, acts as acceptor giving tetra-N-acetylchitotetraose [GlcNAc(beta 1-4)GlcNAc(beta 1-4)GlcNAc(beta 1-4)GlcNAc]. The product mixture consisting of mono-, di-, tri-, and tetrasaccharides is conveniently separated by charcoal-Celite chromatography.

Dynamics of the biosynthesis of methylursubin in plant cells employing in vivo 13CNMR without labelling

In vivo NMR experiments with a digital 600 MHz instrument, exploiting the natural abundance of 13C, allowed us for the first time to follow the biosynthesis of the newly detected glycoside, methylursubin (4-methoxyphenyl-O-beta-D-primeveroside), from 4-methoxyphenol through the intermediate methylarbutin in cell suspensions of the Indian medical plant, Rauwolfia serpentina. The metabolic dynamics indicate that, within 48 hr, 4-methoxyphenol is almost completely converted into the primeveroside, methylursubin. Because of the higher sensitivity at 150.9 MHz compared to that at 100.6 MHz, measuring times could be reduced to 1.5 hr. This allows detailed monitoring of the conversion of 4-methoxyphenol with an excellent signal-to-noise ratio.

The effect of pH and oxygen concentration on the formation of 3-ketodisaccharides by Agrobacterium tumefaciens

The further optimization of 3-ketodisaccharide formation with sucrose, leucrose and iso maltulose was studied with special regard to pH and oxygen concentration in the reaction mixture with resting cells of Agrobacterium tumefaciens. It was found that the optimal pH values for the highest reaction rate and highest yield were different as the pH affected the stability of the 3-keto derivatives formed. A pH shift to 5.0 clearly reduced the enzymatic degradation of the 3-keto derivatives thus stabilizing them. The influence of constant oxygen concentrations on 3-ketosucrose formation was tested showing results not explicable with normal Michaelis-Menten kinetics. For each substrate a maximum of reaction rate and yield were obtained at very low oxygen concentrations.