Effects of size of carbohydrate chain on protease digestion of Aspergillus niger endo-beta-1,4-glucanase

Extremely acidic beta-1,4-glucanase, CelA4, from thermoacidophilic Alicyclobacillus sp. A4 with high protease resistance and potential as a pig feed additive

An acidic endo-beta-1,4-glucanase, denoted CelA4 ( approximately 48 kDa), was purified from thermoacidophilic Alicyclobacillus sp. A4. Two internal peptides of CelA4 showed strong sequence identity to the Alicyclobacillus acidocaldarius cellulase precursor and contained the conserved domain and catalytic region of glycoside hydrolase family 51 beta-1,4-glucanases, and the N-terminal and three other internal peptides had no close glucanase or cellulase relatives, suggesting that the enzyme might be novel. CelA4 had broad substrate specificity, exhibited maximum activity at 65 degrees C and pH 2.6, was stable over pH 1.8-7.6, and showed strong resistance to acidic and neutral proteases, notably pepsin. In comparison to the commercial endo-beta-1,3-1,4-glucanase, CelA4 was more stable, released more reducing sugar from barley beta-glucan, and under simulated gastric conditions, decreased the viscosity of barley-soybean feed to a greater extent. These properties make CelA4 a good candidate as a new commercial glucanase to improve the nutrient bioavailability of pig feed.

Transglycosylation activity of the endo-beta-1,4-glucanase from Aspergillus niger IFO31125 and its application

Endo-beta-1,4-glucanase from Aspergillus niger was found to have an endo-type transglycosylation activity. The enzyme effectively transferred cellooligosaccharide residues to various 1-alkanols in the presence of cellopentaose as the oligosaccharide donor. By incubating the enzyme with 1-octanol and cellopentaose in the presence of acetonitrile, 1-octyl-cellotrioside was synthesized. The product was isolated by silica gel column chromatography and analyzed by mass spectrometry. p-NP-beta-Glc, p-NP-beta-Gal, p-NP-beta-GlcNAc, Ser, and Thr were also possible acceptors for the transglycosylation activity of the enzyme.

Determination of glycosylation sites, disulfide bridges, and the C-terminus of Stereum purpureum mature endopolygalacturonase I by electrospray ionization mass spectrometry

Stereum purpureum endopolygalacturonase (endoPG; EC 3.2.1.15) is a causal protein for silver-leaf disease in apple trees. Endopolygalacturonase I, is a mixture of three components (Ia, Ib, and Ic) that produce three bands on SDS/PAGE but have the same polypeptide and sugar chains. Electrospray ionization mass spectrometry (ESI-MS) analysis of three endoPG I proteins and deglycosylated endoPG Ia revealed a molecular mass of 37 068, 38 285, and 39 503 for Ia, Ib, and Ic, respectively; the number of N-binding sugar chains matches that of a high-mannose type of sugar chain. Two, three, and four sugar chains are present in endoPG Ia, Ib, and Ic, respectively. Deletion of 44 amino acids from the deduced sequence occurred in the C-terminal region. Positions of the glycosylation sites and disulfide bridges were decided by tryptic digestion followed by liquid chromatography-electrospray mass spectrometry (LC-ESI-MS) analysis of reductive and nonreductive pyridylethylated endoPG I proteins. The glycosylated asparagines were determined to be Asn92 and 161; Asn92, 161, 279, or 302; and Asn92, 161, 279, and 302 in Ia, Ib, and Ic, respectively. Three disulfide bridges were noted at Cys3-Cys17, Cys175-Cys191, and Cys300-Cys303. These results are the first findings for fungal endoPG and may contribute to clarification of the relationship between stereostructure and catalytic activity.

Effects of carbohydrate chain on surface net charge and hydrophobicity of glycoenzymes

Three different carbohydrate-depleted enzymes were prepared from an endo-beta-1,4-glucanase of Aspergillus niger IFO31125 by treatment with endo-beta-N-acetylglucosaminidase or alpha-mannosidase. The molecular sizes of these enzymes decreased from 40 kDa containing about 8.9% carbohydrate to 39, 38, and 37 kDa with carbohydrate at 4.5, 1.3, and 0.8% (w/w), respectively. The surface net charges on these enzyme preparations were calculated from their electrophoretic mobilities measured by capillary zone electrophoresis. They had increased negative charges corresponding to the decreases in the carbohydrate content; those of native and 37-kDa enzymes were about -0.03 and -0.045, respectively. The surface hydrophobicities of proteins were also measured by partitioning the enzymes in a two-phase system containing polyethylene glycol and dextran, and decreased corresponding with decreases in their carbohydrate content. The results indicated that the high mannose type of carbohydrate chain in endo-beta-1,4-glucanase affected the surface net charge on the enzyme and increased the surface hydrophobicity.