Specific inhibition of endo-beta-N-acetylglucosaminidase D by mannose and simple mannosides

Tools to cleave glycoproteins

There are a variety of enzymes available that are able to cleave glycoproteins, including enzymes that are specific for carbohydrate-carbohydrate linkages, carbohydrate-protein bonds and the peptide backbone. Such enzymes are useful for determining the sites of glycosylation within proteins, and for releasing glycan structures for subsequent carbohydrate analysis. One protease has been identified as being specific for O-sialoglycoproteins and can be used to identify such molecules and their epitope regions. The lack of cytotoxicity and the narrow specificity of this enzyme provides an improved method for the immunomagnetic selection of human bone-marrow stem-cells.

Comparing the glycosylation patterns of recombinant glycoproteins

The glycosylation profile of a recombinant glycoprotein can not only significantly affect its therapeutic profile, but is also extremely sensitive to cell-culture and purification conditions. To define glycosylation patterns and to ensure consistency of recombinant glycoproteins among different preparations requires highly sensitive and reproducible analytical methods that can be used routinely. New strategies and instrumentation are being developed which should allow such analysis to be largely automated.

Specificity towards oligomannoside and hybrid type glycans of the endo-beta-N-acetylglucosaminidase B from the basidiomycete Sporotrichum dimorphosporum

We have previously shown that an endo-beta-N-acetylglucosaminidase (EC 3.2.1.96) named "Endo B", isolated from culture filtrates of the basidiomycete Sporotrichum dimorphosporum cleaves asialo-, and to some extent, monosialylated bi-antennary glycans of the N-acetyllactosamine type linked to the asparagine residue of peptide or protein moieties [Bouquelet S, Strecker G, Montreuil J, Spik G (1980) Biochimie 62:43-49]. In the present paper, the substrate specificity of the enzyme towards oligomannoside and hybrid type glycans has been analyzed. The results obtained indicate that ovalbumin glycopeptides containing four to seven mannose residues and bovine lactotransferrin glycopeptides containing four to nine mannose residues were completely hydrolyzed by the enzyme. The degree of cleavage was variable among hybrid type structures, since glycopeptides containing the following glycans: (Gal)1(GlcNAc)3(Man)5(GlcNAc)2; (GlcNAc)3(Man)5(GlcNAc)2;(GlcNAc)3(Man)4(GlcNAc)2 were not hydrolyzed by the enzyme while the percentage of hydrolysis of a glycopeptide containing (GlcNAc)2(Man)5(GlcNAc)2 glycan reached 90%. The bovine lactotransferrin was partially deglycosylated (40%) in the absence of non-ionic detergent while native ovalbumin glycoprotein was not hydrolyzed by the enzyme. The oligomannoside- and the N-acetyllactosamine-type degrading activities present in the culture filtrates were not separated at any step of the purification procedure. Both activities were eluted as a single component with an apparent molecular mass of 89 kDa suggesting that they are located on the same enzyme molecule. Endo B represents a powerful tool for removing oligomannoside- and N-acetyllactosamine-type glycans from N-glycopeptides and N-glycoproteins. Moreover, advantages in the use of Endo B in a soluble form as well as in an immobilized form result in its high activity and in its stability to heat denaturation and storage.

The removal of carbohydrates from ricin with endoglycosidases H, F and D and alpha-mannosidase

Recently, several investigators have explored the possibility of targeting ricin to designated cell types in animals by its linkage to specific antibodies. There is evidence, however, that the mannose-containing oligosaccharide chains on ricin are recognised by reticuloendothelial cells in the liver and spleen and so cause the immunotoxins to be removed rapidly from the blood stream. In the present study we analysed the carbohydrate composition of ricin and examined enzymic methods for removing the carbohydrate. The carbohydrate analysis ricin A-chain revealed the presence of one residue of xylose and one of fucose in addition to mannose and N-acetylglucosamine which had been detected previously. The B-chain contained only mannose and N-acetylglycosamine. Ricin A-chain is heterogeneous containing two components of molecular weight 30 000 and 32 000. Strong evidence was found that the heavier form of the A-chain contains an extra carbohydrate unit which is heterogeneous with respect to concanavalin A binding and sensitivity to endoglycosidase H. The lower molecular weight form of A-chain did not bind concanavalin A and was insusceptible to endoglycosidases. Only one of the two high mannose oligosaccharide units on the isolated B-chain could be removed by endoglycosidases H or F, whereas both were removable after denaturation of the polypeptide by SDS. Both the isolated A- and B-chains were sensitive to alpha-mannosidase. Intact ricin was resistant to endoglycosidase treatment and was only slightly sensitive to alpha-mannosidase. The addition of SDS allowed endoglycosidase H to remove both of the B-chain oligosaccharides from intact ricin and increased the toxin's sensitivity to alpha-mannosidase. In conclusion, extensive enzymic deglycosylation of ricin may only be possible if the A- and B-chains are first separated, treated with enzymes and then recombined to form the toxin.

Primary structure of N-glycosidically linked asialoglycans of secretory immunoglobulins A from human milk

The asialoglycopeptides obtained from secretory immunoglobulins A from human milk have been separated by gel filtration and affinity chromatography on Concanavalin A-Sepharose and Lens culinaris agglutinin-Sepharose columns. Their structures have been determined by sugar analysis, methylation studies including mass spectrometry and 500-MHz 1H-NMR spectroscopy. The glycans are of the biantennary N-acetyllactosamine type differing in their degree of extension by fucosyl-N-acetyllactosamine residues. The overall structures of the glycopeptides are as follows: (Formula: see text) Most of the asialoglycopeptide structures possess an intersecting GlcNAc residue; they are suggested to be located on the alpha chain of the secretory immunoglobulins A of human milk. The non-intersected structures probably occur on the secretory piece. The methodology applied to the structural analysis adequately coped with the extremely high degree of heterogeneity shown by the structures.

Purification and characterization of an extracellular beta-n-acetylhexosaminidase from Paecilomyces persicinus

Both beta-N-acetylglucosaminidase nad beta-N-acetylgalactosaminidase activities were detected in the culture fluids of Paecilomyces persicinus P-10 after growth in a soybean meal-corn meal medium. The active material was purified by means of protamine sulfate fractionation and ultrafiltration, followed by ion exchange and gel chromatography. The ratio of the two activities remained constant throughout the purification, and the final product was shown to migrate as a single band by using gel isoelectric focusing, disc electrophoresis, and detergent gel electrophoresis. Temperature, pH, inhibition, and kinetic studies were performed to characterize both activities. The molecular weight of the enzyme was estimated to be about 100,000 by high-resolution gel chromatography. Based on the data obtained, it is suggested that both beta-N-acetylglucosaminidase and beta-N-acetylgalactosaminidase activities reside in the same protein.