Induction and Purification of Endo-β-N-Acetylglucosaminidase from Arthrobacter protophormiae Grown in Ovalbumin

Arthrobacter protophormiae produced a high level of extracellular endo-β-N-acetylglucosaminidase when cells were grown in a medium containing ovalbumin. The enzyme was induced by the glycopeptide fraction of ovalbumin prepared by pronase digestion. Production of the enzyme was also induced by glycoproteins such as yeast invertase and bovine ribonuclease B but not by monosaccharides such as mannose, N-acetylglucosamine, and galactose. The enzyme was purified to homogeneity as demonstrated by polyacrylamide gel electrophoresis and has an apparent molecular weight of about 80,000. The enzyme showed a broad optimum pH in the range of pH 5.0 to 11.0. The enzyme hydrolyzed all heterogeneous ovalbumin glycopeptides, although the hydrolysis rates for hybrid type glycopeptides were very low. The substrate specificity of A. protophormiae endo-β-N-acetylglucosaminidase was very similar to that of Endo-C_II from Clostridium perfringens. Therefore, the enzyme induction by A. protophormiae seems to have a close relation to the substrate specificity of the enzyme.     

Purification and characterization of endo-beta-N-acetylglucosaminidase of Aspergillus oryzae

An endo-beta-N-acetylglucosaminidase which hydrolyzes the N,N'-diacetylchitobiosyl linkage in asparagine-linked oligosaccharides was purified from the enzyme product of Aspergillus oryzae. Its substrate specificity was similar to that of endo-beta-N-acetylglucosaminidase H from Streptomyces griseus with respect to the relative activities toward the glycopeptides obtained from ovalbumin and bovine IgG. The present endoglycosidase exhibited a broad optimum pH range and was relatively stable. Metal ions, chelating agents and D-mannose did not have a significant effect on the enzyme activity.     

Determination of glycosylation sites using a protein sequencer and deglycosylation of native yeast invertase by endo-beta-N-acetylglucosaminidase.

Endo-beta-N-acetylglucosaminidase from Arthrobacter protophormiae was tested for its capacity to release N-linked sugar chains from native yeast invertase. The enzyme liberated about 80% of the sugar chains from the native invertase. Deglycosylated invertase was digested by chymotrypsin or pepsin, and twelve N-acetylglucosamine-containing glycopeptides were isolated. The amino acid sequences of these glycopeptides were analyzed by a protein sequencer, and the elution position of 4-L-aspartylglycosylamine was directly identified by conventional sequencing. The endo-beta-N-acetylglucosaminidase was found to remove mainly nine sugar chains from native invertase.     

Synthesis of neoglycoenzymes with homogeneous N-linked oligosaccharides using immobilized endo-beta-N-acetylglucosaminidase A

A procedure for the enzymatic synthesis of neoglycoenzymes is described. The gene encoding endo-beta-N-acetylglucosaminidase from Arthrobacter protophormiae (Endo-A) was overexpressed in Escherichia coli as a fusion protein linked to glutathione S-transferase (GST). GST-Endo-A fusion was extracted as a soluble protein. The fusion protein was purified to homogeneity with glutathione-Sepharose 4B and showed transglycosylation activity toward high-mannose-type glycopeptides without removing the GST moiety. The GST-Endo-A immobilized on glutathione-Sepharose 4B retained its transglycosylation activity. The immobilized enzyme could transfer (Man)(6)GlcNAc en bloc to partially deglycosylated ribonuclease B without damaging its enzyme activity. The immobilized GST-Endo-A should be very useful for synthesizing active neoglycoenzymes attached with homogeneous N-linked oligosaccharides.     

The use of mannan-Sepharose 4B affinity chromatography for the purification of endo-beta-N-acetylglucosaminidase from Bacillus alvei

In order to facilitate the isolation of endo-beta-N-acetylglucosaminidase for the structural analysis of glycoconjugates, we have isolated a strain of Bacillus alvei which produces a high level of endo-beta-N-acetylglucosaminidase. We have also devised a simple procedure for the purification of endo-beta-N-acetylglucosaminidase from B. alvei using mannan-Sepharose affinity chromatography. By using this method, endo-beta-N-acetylglucosaminidase was purified 3300-fold with 85% yield from the crude enzyme obtained by ammonium sulfate precipitation of the culture medium. The molecular weight of this enzyme was estimated to be about 66 000 by gel filtration. When using (Man)6(GlcNAc)2-Asn-Dns as substrate, the optimal activity occurs at pH 6.5 with Km of 1.9 mM. The action of endo-beta-N-acetylglucosaminidase toward several glycopeptides was also studied.     

Chemo-enzymatic synthesis of eel calcitonin glycosylated at two sites with the same and different carbohydrate structures

Naturally occurring glycopeptides and glycoproteins usually contain more than one glycosylation site, and the structure of the carbohydrate attached is often different from site to site. Therefore, synthetic methods for preparing peptides and proteins that are glycosylated at multiple sites, possibly with different carbohydrate structures, are needed. Here, we report a chemo-enzymatic approach for accomplishing this. Complex-type oligosaccharides were introduced to the calcitonin derivatives that contained two N-acetyl-D-glucosamine (GlcNAc) residues at different sites by treatment with Mucor hiemalis endo-beta-N-acetylglucosaminidase. Using this enzymatic transglycosylation reaction, three glycopeptides were produced, a calcitonin derivative with the same complex-type carbohydrate at two sites, and two calcitonin derivatives each with one complex-type carbohydrate and one GlcNAc. Starting from the derivatives with one complex-type carbohydrate and one GlcNAc, a high-mannose-type oligosaccharide was successfully transferred to the remaining GlcNAc using another endo-beta-N-acetylglucosaminidase from Arthrobacter protophormiae. Thus, we were able to obtain glycopeptides containing not only two complex-type carbohydrates, but also both complex and high-mannose-type oligosaccharides in a single molecule. Using the resultant glycosylated calcitonin derivatives, the effects of di-N-glycosylation on the structure and the activity of calcitonin were studied. The effect appeared to be predictable from the results of mono-N-glycosylated calcitonin derivatives.     

A novel disaccharide substrate having 1,2-oxazoline moiety for detection of transglycosylating activity of endoglycosidases

A disaccharide substrate of Manbeta1-4GlcNAc-oxazoline 2 was designed and synthesized as a novel probe for detection of the transglycosylating activity of endoglycosidases. A regio- and stereoselective transglycosylation reaction of 2 to GlcNAcbeta1-O-pNP or Dns-Asn(GlcNAc)-OH catalyzed by endo-beta-N-acetylglucosaminidase from Mucor hiemalis (Endo-M) and endo-beta-N-acetylglucosaminidase from Arthrobacter protophormiae (Endo-A) has been demonstrated for the first time, resulting in the core trisaccharide derivative Manbeta1-4GlcNAcbeta1-4GlcNAcbeta1-O-pNP 8 (or -(Dns)Asn-OH). Interestingly, the transglycosylation proceeds irreversibly; the resulting trisaccharide 8 was not hydrolyzed by Endo-M and Endo-A. Based on these results, a new mechanism including an oxazolinium ion intermediate has been proposed for the endoglycosidase-catalyzed hydrolysis or transglycosylation.     

Studies on Turbatrix aceti beta-N-acetylglucosaminidase. 1. Purification and physicochemical characterization

N-Acetyl-beta-D-glucosaminidase was purified, from the culture medium of the nematode Turbatrix aceti, to homogeneity, as judged by electrophoresis in polyacrylamide gel and ultracentrifugation. The purification scheme involved the following steps: (i) concentration of the culture medium by ultra-filtration by an Amicon PM-30 membrane; (ii) ammonium sulfate precipitation; (iii) DEAE-Sephadex and (iv) Sephadex G-200 chromatography; and (v) affinity chromatography on succinyldiaminopropyl amino-Sepharose bearing the ligand p-aminophenyl 2-acetamido-2-deoxy-1-thio-beta-D-glucopyranoside. The molecular weight of the enzyme was 112,000 +/- 4800 and 124,000 as determined by polyacrylamide gel electrophoresis and by gel filtration through Sephacryl S-200, respectively. The enzyme showed a pH optimum of 4.8 for N-acetylglucosaminidase and 5.4 for N-acetylgalactosaminidase. The detailed substrate specificity studies were carried out on both synthetic and natural oligosaccharides and glycopeptides. The chitin oligosaccharides and asialo-agalacto complex type as well as high mannose-type glycoproteins such as fetuin and ovalbumin, respectively, were good substrates for the enzyme. Substrate analogs in which the oxygen atom of the acetamido group was replaced by sulfur atom proved to be poor substrates.     

Identification of an endo-beta-N-acetylglucosaminidase gene in Caenorhabditis elegans and its expression in Escherichia coli

We report the identification, molecular cloning, and characterization of an endo-beta-N-acetylglucosaminidase from the nematode Caenorhabditis elegans. A search of the C. elegans genome database revealed the existence of a gene exhibiting 34% identity to Mucor hiemalis (a fungus) endo-beta-N-acetylglucosaminidase (Endo-M). Actually, the C. elegans extract contained endo-beta-N-acetylglucosaminidase activity. The putative cDNA for the C. elegans endo-beta-N-acetylglucosaminidase (Endo-CE) was amplified by polymerase chain reaction from the Uni-ZAP XR library, cloned, and sequenced. The recombinant Endo-CE expressed in Escherichia coli exhibited substrate specificity mainly for high-mannose type oligosaccharides. Man(8)GlcNAc(2) was the best substrate for Endo-CE, and Man(3)GlcNAc(2) was also hydrolyzed. Biantennary complex type oligosaccharides were poor substrates, and triantennary complex substrates were not hydrolyzed. Its substrate specificity was similar to those of Endo-M and endo-beta-N-acetylglucosaminidase from hen oviduct. Endo-CE was confirmed to exhibit transglycosylation activity, as seen for some microbial endo-beta-N-acetylglucosaminidases. This is the first report of the molecular cloning of an endo-beta-N-acetylglucosaminidase gene from a multicellular organism, which shows the possibility of using this well-characterized nematode as a model system for elucidating the role of this enzyme.     

Enzymatic synthesis of novel oligosaccharides by use of transglycosylation activity of endo-beta-N-acetylglucosaminidase from Arthrobacter protophormiae.

The transglycosylation activity of endo-beta-N-acetylglucosaminidase from Arthrobacter protophormiae was used for the enzymatic synthesis of novel oligosaccharides. When (Man)6(GlcNAc)2Asn was used as a substrate for the transglycosylation, (Man)6GlcNAc-Glc, (Man)6GlcNAc-Man, (Man)6GlcNAc-chitobiose, and (Man)6GlcNAc-gentiobiose were synthesized. Their structures were identified by HPLC, ion spray mass spectrometry, and digestion with glycosidases. Endo-beta-N-acetylglucosaminidases hydrolyzed the pyridylamino derivatives of these oligosaccharides.     

Endo-beta-N-acetylglucosaminidases acting on carbohydrate moieties of glycoproteins: purification and properties of the two enzymes with different specificities from Clostridium perfringens.

Two endo-β-N-acetylglucosaminidases (C_I and C_I) acting on carbohydrate moieties of glycoproteins were highly purified from the culture fluid of Clostridium perfringens. C_I had the substrate specificity indistinguishable from that of endo-β-N-acetylglucosaminidase D from Diplococcus pneumoniae. C_II showed the specificity similar to that of endo-β-N-acetylglucosaminidase H from Streptomyces griseus but is distinct from the streptomyces enzyme with respect to the relative activity toward ovalbumin glycopeptides and Unit A glycopeptides of thyroglobulin. Both enzymes from C. perfringens were most active at neutral pH and were inhibited by p-chloromercuriphenylsulfonate.     

Characterization of endo-beta-N-acetylglucosaminidase from alkaliphilic Bacillus halodurans C-125

The genome sequencing project on alkaliphilic Bacillus halodurans C-125 revealed a putative endo-beta-N-acetylglucosaminidase (Endo-BH), which consists of a signal peptide of 24 amino acids, a catalytic region of 634 amino acids exhibiting 50.1% identity with the endo-beta-N-acetylglucosaminidase from Arthrobacter protophormiae (Endo-A), and a C-terminal tail of 220 amino acids. Transformed Escherichia coli cells carrying the Endo-BH gene exhibited endo-beta-N-acetylglucosaminidase activity. Recombinant Endo-BH hydrolyzed high-mannose type oligosaccharides and hybrid type oligosaccharides, and showed transglycosylation activity. On deletion of 219 C-terminal amino acid residues of Endo-BH, the wild type level of activity was retained, whereas with deletions of the Endo-A homolog domain, the proteins were expressed as inclusion bodies and these activities were reduced. These results suggest that the enzymatic properties of Endo-BH are similar to those of Endo-A, and that the C-terminal tail does not affect the enzyme activity. Although the C-terminal tail region is not essential for enzyme activity, the sequence is also conserved among endo-beta-N-acetylglucosaminidases of various origins.     

Almond glycopeptidase acting on aspartylglycosylamine linkages. Multiplicity and substrate specificity

The glycopeptide preparation that has been isolated from almond emulsin and acts on β-aspartylglycosylamine linkages in glycopeptides was separated into three active fractions by DEAE-cellulose column chromatography. The three discrete species of glycopeptidase (Groups A, B and C) have been purified 30-, 136- and 99-fold, respectively. The optimum pH value of Group A was 6.0 and those of Groups B and C, 5.0. Isoelectric points of Groups A, B and C were pH 7.7, 8.6 and 8.7, respectively. All three glycopeptidases hydrolyzed quantitatively glycopeptides with 3.11 amino acid residues prepared from stem bromelain, ovalbumin and ovotransferrin. Group C preferred glycopeptides with shorter peptide chains, whereas Groups A and B preferred those with longer chains. Glycopeptidase Group A also hydrolyzed intact glycoproteins such as stem bromelain, ovalbumin, Taka-amylase A and desialyted human transferrin.     

Mannosyl Transfer by Membranes of Aspergillus niger: Mannosylation of Endogenous Acceptors and Partial Analysis of the Products

A smooth membrane fraction of Aspergillus niger catalyzed the transfer of mannose from GDP-mannose to endogenous lipid and protein acceptors. The mannolipid was acidic, as judged by diethylaminoethyl-cellulose chromatography, and had a mobility similar to ficaprenyl phosphate on thin-layer chromatograms. Mannose transfer occurred optimally at pH 6.5 to 7.5 and required Mn(2+) for use of the protein as acceptor, but either Mn(2+) or Mg(2+) with the lipid as acceptor. Glycopeptides of the mannosylated protein ([(14)C]gly) and of an alpha-glucosidase (alpha-glu) secreted by the organism were produced by Pronase digestion and separation of the products on Sephadex G-25. Because ovalbumin has a carbohydrate composition similar to that of alpha-glu and because the carbohydrate structure of ovalbumin is known, ovalbumin glycopeptides (Ov) were similarly obtained and used as standards in determining carbohydrate structures. Oligosaccharide chains of [(14)C]gly, alpha-glu, and Ov were obtained by treatment of the respective glycopeptides with endo-beta-N-acetylglucosaminidase, reduction with NaBT(4), and concanavalin A-Sepharose chromatography. The (3)H-labeled oligosaccharides obtained were subjected to the following treatments: (i) digestion with alpha- and beta-mannosidases, (ii) Smith degradation, and (iii) acetolysis. Subsequently, changes in paper chromatographic mobilities were detected. Also, alpha-glu was permethylated, and the partially methylated alditol acetates were analyzed by gas-liquid chromatography. The resultant proposed structure shows that the oligosaccharide chain of alpha-glu is almost identical to that of an Ov chain, while [(14)C]gly has a structure which is probably the same as that of alpha-glu. It is suggested that the transferase(s) involved in [(14)C]gly synthesis in vitro may be responsible for glycosylation of secreted enzymes.     

Assay of glycoamidases and endo-beta-N-acetylglucosaminidases by lectin capture and dissociation-enhanced lanthanide fluorescence immunoassay

We have developed an assay system for endo-beta-N-acetylglucosaminidase and glycoamidase (PNGase), using Eu(3+)-labeled Man(9)GlcNAc(2) glycopeptides as substrates in combination with lectin capture. Two glycopeptides of different peptide lengths, derived from soybean agglutinin, were labeled with Eu(3+) via a diethylenetriaminepentaacetate (DTPA) chelating linker and served as substrates for two types of enzymes: one with (Man(9)GlcNAc(2))Asn for endo-beta-N-acetylglucosaminidase and the other with Ala-Ser-Phe-(Man(9)GlcNAc(2))Asn-Phe-Thr for glycoamidase activities. Following enzymatic hydrolysis, concanavalin A, immobilized or soluble, was added to the mixture to bind unreacted substrate and unlabeled hydrolysis product. The labeled peptide product could then be separated from the lectin-bound complexes by filtration for quantification by dissociation-enhanced lanthanide fluorescence immunoassay. Activities as low as 2 fmol min(-1) could be rapidly quantified for both types of enzymes, and enzymological parameters could be determined within minutes. Applicability of the assay was tested for identification of a glycoamidase activity peak in the fractionation of sweet almond emulsin, a classic example. This assay offers sensitivity, ease of use, and high throughput. In addition, it is versatile and should be applicable to other glycobiology enzyme systems.     

Arylsulfatase A from human tissues contains an endo-beta-N-acetylglucosaminidase F-resistant oligosaccharide

Homogeneous arylsulfatase A from human placenta, liver and urine contains two nonidentical subunits of 59 and 54 kDa. The two subunits are immunologically identical. The relative amount of low molecular weight subunits is only 20-30% of the total enzyme protein. Treatment of the enzyme under various conditions with endo-beta-N-acetylglucosaminidase F results in a decrease in the apparent molecular weight of both subunits by 1-2 kDa. a value that corresponds to the loss of a single N-linked oligosaccharide. However, as judged by carbohydrate staining, endo-beta-N-acetylglucosaminidase F does not remove all carbohydrate from the subunits or from glycopeptides of arylsulfatase A. In contrast, human prostatic acid phosphatase, a glycoprotein with a high content of mannose, hybrid and complex oligosaccharides is completely deglycosylated under identical experimental conditions. Several attempts to deglycosylate arylsulfatase A by chemical methods were unsuccessful due to poor recovery of the protein. From the present studies we conclude that arylsulfatase A contains an endo-beta-N-acetylglucosaminidase F resistant, perhaps O-linked carbohydrate.     

Partial purification and characterization of an endo-alpha-N-acetylgalactosaminidase from the culture of medium of Diplococcus pneumoniae.

The culture medium of Diplococcus pneumoniae contains enzymic activity that cleaves Galbeta1 leads to 3GalNAc from desialized human erythrocyte membrane glycoprotein. The enzyme was purified 180-fold by ammonium sulfate fractionation, gel filtration through a Sephadex G-200 column, and DEAE A-25 Sephadex chromatography. The purified enzyme liberates Galbeta1 leads to 3GalNAc from glycopeptides and glycoproteins with Galbeta1 leads to 3GalNAcalpha1 leads to Ser and Thr moieties. The optimum pH of this enzyme is 6.0. Using glycopeptides obtained by trypsin digestion of human erythrocyte membrane glycoprotein as a substrate, a Km of 0.20 mM (on the basis of the amount of Galbeta1 leads to 3GalNAc residues) was obtained. So far, the enzyme appears to have a strict specificity for Galbeta1 leads to 3GalNAcalpha1 leads to Ser and Thr structures, because no oligosaccharides larger than trisaccharides were liberated from porcine submaxillary mucin.     

Identification of amino acid residues essential for the substrate specificity of Flavobacterium sp. endo-beta-N-acetylglucosaminidase

The gene encoding the endo-beta-N-acetylglucosaminidase from Flavobacterium sp. (Endo-Fsp) was sequenced. The Endo-Fsp gene was overexpressed in Escherichia coli cells, and was purified from inclusion bodies after denaturation by 8 M urea. The renatured Endo-Fsp had the same optimum pH and substrate specificity as the native enzyme. Endo-Fsp had 60% sequence identity with the endo-beta-N-acetylglucosaminidase from Streptomyces plicatus (Endo-H), and the putative catalytic residues were conserved. Site-directed mutagenesis was done at conserved residues based on the three-dimensional structure and mutagenesis of Endo-H. The mutant of Glu-128, corresponding to Glu-132 in Endo-H and identified as an active site residue, was inactivated. Mutagenesis around the predicted active site of Endo-Fsp reduced the enzymatic activity. Moreover, the hydrolytic activity toward hybrid-type oligosaccharides was decreased compared to that toward high-mannose type oligosaccharides by mutagenesis of Asp-126 and Asp-127. Therefore, site-directed mutagenesis of some of these conserved residues indicates that the predicted active sites are essential to the enzymatic activity of Endo-Fsp, and may have similar roles in catalysis as their counterparts in Endo-H.     

Glycopeptide probes for understanding peptide specificity of the folding sensor enzyme UGGT

A systematic series of chitobiose-modified pentapeptides with sequence variations of hydrophobic leucine and hydrophilic serine were synthesized. The resulting glycopeptides were used as molecular probes to elucidate aglycon peptide specificity of the glycoprotein-folding sensor enzyme UGGT. Inhibitory experiments with a synthetic fluorescent glyco-substrate and the glycopeptides revealed that UGGT prefers a serine residue directly linked to C-terminal of the N-glycosylation site in its substrate recognition.     

Microbial endo-beta-N-acetylglucosaminidases acting on complex-type sugar chains of glycoproteins.

The activity and substrate specificity of endo-beta-N-acetylglucosaminidase [glycopeptide-D-mannosyl-N4-(N-acetyl-D-glucosaminyl)2-asparagine 1,4-N-acetyl-beta-glucosamino-hydrolase, EC 3.2.1.96] obtained from Mucor hiemalis (Endo-M) was compared with that of the enzyme obtained from Flavobacterium meningosepticum (Endo-F), which is the only enzyme available that acts on the complex oligosaccharides of asparagine-linked sugar chains in glycoproteins. They showed almost the same activities toward DNS-ovalbumin glycopeptide containing high-mannose and hybrid asparagine-linked oligosaccharides. However, Endo-M showed high activity towards DNS-asialotransferrin and DNS-transferrin glycopeptides, which contain complex biantennary oligosaccharides. Endo-M could weakly act even on DNS-asialofetuin glycopeptide containing complex triantennary oligosaccharides, while Endo-F could not. SDS-denatured asialotransferrin was deglycosylated by both enzymes in the presence of non-ionic detergent (NP-40) and EDTA, and the deglycosylated protein migrated to a lower molecular weight position than asialotransferrin on SDS-PAGE. However, even in the absence of detergent, Endo-M deglycosylated native asialotransferrin and transferrin. Deglycosylation of asialotransferrin was confirmed by means of Con A-Sepharose 4B column chromatography and SDS-PAGE.