Characterization and synthetic application of a novel beta1,3-galactosyltransferase from Escherichia coli O55:H7.

A beta1,3-galactosyltransferase (WbgO) was identified in Escherichia coli O55:H7. Its function was confirmed by radioactive activity assay and structure analysis of the disaccharide synthesized with the recombinant enzyme. WbgO requires a divalent metal ion, either Mn(2+) or Mg(2+), for its activity and is active between pH 6.0-8.0 with a pH optimum of 7.0. N-acetylglucosamine (GlcNAc) and oligosaccharides with GlcNAc at the non-reducing end were shown to be its preferred substrates and it can be used for the synthesis of type 1 glycan chains from these substrates. Together with a recombinant bacterial GlcNAc-transferase, benzyl beta-lacto-N-tetraoside was synthesized with the purified WbgO to demonstrate the synthetic utility of WbgO.

Structural basis and catalytic mechanism for the dual functional endo-beta-N-acetylglucosaminidase A.

Endo-beta-N-acetylglucosaminidases (ENGases) are dual specificity enzymes with an ability to catalyze hydrolysis and transglycosylation reactions. Recently, these enzymes have become the focus of intense research because of their potential for synthesis of glycopeptides. We have determined the 3D structures of an ENGase from Arthrobacter protophormiae (Endo-A) in 3 forms, one in native form, one in complex with Man(3)GlcNAc-thiazoline and another in complex with GlcNAc-Asn. The carbohydrate moiety sits above the TIM-barrel in a cleft region surrounded by aromatic residues. The conserved essential catalytic residues - E173, N171 and Y205 are within hydrogen bonding distance of the substrate. W216 and W244 regulate access to the active site during transglycosylation by serving as "gate-keepers". Interestingly, Y299F mutation resulted in a 3 fold increase in the transglycosylation activity. The structure provides insights into the catalytic mechanism of GH85 family of glycoside hydrolases at molecular level and could assist rational engineering of ENGases.

[Construction of the Man8 GlcNAc2 glycosylation Saccharomyces cerevisiae mutant strain].

In Saccharomyces cerevisiae, protein glycosylation passed two different N-linked modification pathways after the export of predominantly Man8 GlcNAc2-containing glycoproteins from ER to the Golgi. The core oligosaccharide undergoes maturation in the Golgi resulting in a Man8-13 GlcNAc2 structure. Alternatively, core structures may be hypermannosylated with up to 200 mannose residues composing of a backbone of alpha1,6-mannosyl residues with branched alpha1, 2- and alpha1,3-mannosyl side chains. Mnn1p and Och1p play an important role in this process. The null disruption of MNN1, OCH1 was replaced by the S. cerevisiae URA3, HIS3, respectively. To characterize the N-glycosylation in the mnn1 och1 mutant, mannoproteins were obtained by hot citrate buffer extraction after the mnn1 och1 cells were crumbled. The extracted mannoprotein was precipitated by ethanol, and further purified by concanavalin A-sepharose 4B. The N-oligomannose saccharides were released from mannoprotein by PNGase F digestion, and then peptides and detergents were removed by passage through ion exchange columns. For desalting, glycans were applied to porous graphitic-carbon cartridge. 2-aminopyridine pyridylaminated sugars were profiled and purified by size fractionation HPLC with Shim-pack cle-NH2 column, and result showed dominantly a single peak. MALDI TOF/MS analysis ofthis peak revealed that its molecular weight was 1796.5Da, which corresponds to the calculated mass of Man8 GlcNAc2-PA. These results indicated that disruptions of MNN1 and OCH1 eliminated the hypermannosylation of the N-linked glycans, and glycoproteins were glycosylated with a single core type glycan, Man8 GlcNAc2, in the mnn1 och1 mutant.

A new fermentation process allows large-scale production of tetra-N-acetyl-chitotetraosyl allosamizoline.

A new compound 2, possessing a tetra-N-acetyl-chitotetraosyl moiety as a constituent, was synthesized by bacterial fermentation, which used allosamizoline 1 as the initial acceptor. A 2-binding chitinase assay, indicated that the chitinase was inactivated by 2 with IC50 = 0.03 microg/mL.

Immobilization of UDP-galactose 4-epimerase from Escherichia coli on the yeast cell surface.

UDP-galactose 4-epimerase (EC 5.1.3.2, Gal E) from Escherichia coli catalyzes the reversible reaction between UDP-galactose and UDP-glucose. In this study, the Gal E gene from E. coli, coding UDP-galactose 4-epimerase, was cloned into pYD1 plasmid and then transformed into Saccharomyces cerevisiae EBY100 for expression of Gal E on the cell surface. Enzyme activity analyses with EBY100 cells showed that the enzyme displayed on the yeast cell surface was very active in the conversion between UDP-Glc and UDP-Gal. It took about 3 min to reach equilibrium from UDP-galactose to UDP-glucose.

Structure-function relations of carbohydrates by neoglycolipid arrays.

The work presented herein is a new noncovalent glycoarray assembly method for microplates created by simply mixing together a carbohydrate and a tetradecylamine. alpha-D-Mannopyranoside, alpha-D-glucopyranoside, and alpha-D-galactopyranoside were utilized in model studies and product formations were detected by lectin binding. The method can be extended to study the steric hindrance effect of carbohydrate-protein interactions, namely the structure-function relations of carbohydrates.

Chemo-enzymatic synthesis of tetra-N-acetyl-chitotetraosyl allosamizoline.

A new compound 7, possessing a tetra-N-acetyl-chitotetraosyl moiety as a constituent, was synthesized by bacterial fermentation which used allosamizoline 6 as the initial acceptor.

Chemo-enzymatic synthesis of allyl penta-N-acetyl-chitopentaose.

Cell density cultivation of recombinant Escherichia coli strains harboring the nodC gene (encoding chitooligosaccharide synthase) from Azorhizobium caulinodans has been previously described as a practical method for the preparation of gram-scale quantities of penta-N-acetyl-chitopentaose. We have now extended this method to the production of allylated derivative of penta-N-acetyl-chitopentaose by using allyl 2-acetamido-2-deoxy-beta-d-glucopyranoside (2) as the initial acceptor for the synthesis of target pentaoside in vivo.

Fabrication and application of neoglycolipid arrays in a microtiter plate.

The work presented herein is a new noncovalent glycoarray assembly method for microplates created by simply mixing together a carbohydrate and a tetradecylamine. Alpha-mannose was utilized in the model study and product formation was detected by lectin binding. The method can be further extended to array complex carbohydrates.

Chemo-enzymatic synthesis of 1,4-oxazepanyl sugar as potent inhibitor of chitinase.

N-acetyl glucosamine 1 is selectively converted into 2 without protection of the other hydroxyl groups by allylation of the anomeric alkoxide in N,N-dimethylformamide containing lithium bromide. We use cell density cultures to produce the allylated derivative of penta-N-acetyl-chitopentaose by using 2 as the initial acceptor for the synthesis of 3 in vivo. Upon periodate oxidation, 3 is transferred to 4. Compound 4 is quickly subjected to sodium borohydride reduction and NH3 amination, which afforded the target compound 5. In 5-binding chitinase assay, it indicates that the chitinase is obviously inactivated by 5 with IC50 = 4.7 micromol/L.

Hydrolysis characteristics of a beta-1,3-D-glucan elicitor from yeast.

Fluorophore-assisted carbohydrate electrophoresis (FACE) is a straightforward, sensitive method for determining the presence and relative abundance of individual (oligo)saccharides in a(n) (oligo)saccharide mixture. The single-terminal aldehydes of oligoglucoside residues released by acid hydrolysis of beta-1,3-D-glucan from yeast were tagged with the charged fluorophore ANTS (8-aminonaphthalene-1,3,6-trisulphonate), and separated with high resolution on the basis of size by PAGE. ANTS fluorescence labelling was not biased by oligoglucoside length; therefore band fluorescence intensity was directly related to the relative abundance of individual oligoglucoside moieties in a heterogeneous sample. FACE analysis revealed that the major oligoglucoside mixture released by acid hydrolysis from beta-1,3-D-glucan was composed of monosaccharide, disaccharide, trisaccharide, tetrasaccharide, pentasaccharide, hexasaccharide, heptasaccharide and octasaccharide, and the order of abundance from high to low was trisaccharide, monosaccharide, disaccharide, tetrasaccharide, pentasaccharide, hexasaccharide, heptasaccharide and octasaccharide respectively. In conclusion, FACE represents an accessible, sensitive and quantitative analytical tool enabling the characterization of a(n) (oligo)saccharide mixture.