Preparation of ß-galacto-oligosaccharides using a novel endo-1,4-ß-galactanase from Penicillium oxalicum.

Endo-1,4-ß-galactanase is an indispensable tool for preparing prebiotic ß-galacto-oligosaccharides (ß-GOS) from pectic galactan resources. In the present study, a novel endo-1,4-ß-galactanase (PoßGal53) belonging to glycoside hydrolase family 53 from Penicillium oxalicum sp. 68 was cloned and expressed in Pichia pastoris GS115. Upon purification by affinity chromatography, recombinant PoßGal53 exhibited a single band on SDS-PAGE with a molecular weight of 45.0 kDa. Using potato galactan as substrate, PoßGal53 showed optimal reaction conditions of pH 4.0, 40 °C, and was thermostable, retaining >80 % activity after incubating below 45 °C for 12 h. Significantly, PoßGal53 exhibited relatively conserved substrate specificity for (1 â†’ 4)-ß-D-galactan with an activity of 6244 ± 282 U/mg. In this regard, the enzyme is in effect the most efficient endo-1,4-ß-galactanase identified to date. By using PoßGal53, ß-GOS monomers were prepared from potato galactan and separated using medium pressure liquid chromatography. HPAEC-PAD, MALDI-TOF-MS and ESI-MS/MS analyses demonstrated that these ß-GOS species ranged from 1,4-ß-D-galactobiose to 1,4-ß-D-galactooctaose (DP 2-8) with high purity. This work provides not only a highly active tool for enzymatic degradation of pectic galactan, but an efficient protocol for preparing ß-GOS.

Cloning, Expression, Purification and Characterization of the ß-galactosidase PoßGal35A from Penicillium oxalicum.

Galactosidases are industrially important enzymes that hydrolyze galactosidic bonds in carbohydrates. Identifying new galactosidases with distinct functional characteristics is of paramount importance. In this study, we report the finding of a novel ß-galactosidase PoßGal35A from the fungus Penicillium oxalicum. PoßGal35A belongs to the glycoside hydrolase family 35 (GH35), functions optimally at 70 °C and pH 5.0, and exhibits a specific high activity (191 ± 6.2 U/mg) towards pNPßgal. Ca2+, Fe3+and Ba2+ ions enhance the activity of the enzyme, whereas Cu2+ and Hg2+ significantly reduce it. This enzyme releases galactose from ß-1,3-galactan, ß-1,4-galactan, ß-1,6-galactan, as well as arabinogalactan from larchwood (LWAG). In addition, PoßGal35A acts synergistically with arabinosidase to degrade LWAG. These results suggest that PoßGal35A is a high activity exo-ß-1,3/4/6-galactanase that can be used to establish glycan blocks in glycoconjugates, and thus provides a new tool for biotechnological applications.

Molecular Cloning and Characterization of a Novel Exo-ß-1,3-Galactanase from Penicillium oxalicum sp. 68.

Arabinogalactans have diverse biological properties and can be used as pharmaceutical agents. Most arabinogalactans are composed of ß-(1→3)-galactan, so it is particularly important to identify ß-1,3-galactanases that can selectively degrade them. In this study, a novel exo-ß-1,3-galactanase, named PoGal3, was screened from Penicillium oxalicum sp. 68, and hetero-expressed in P. pastoris GS115 as a soluble protein. PoGal3 belongs to glycoside hydrolase family 43 (GH43) and has a 1,356-bp gene length that encodes 451 amino acids residues. To study the enzymatic properties and substrate selectivity of PoGal3, ß-1,3-galactan (AG-P-I) from larch wood arabinogalactan (LWAG) was prepared and characterized by HPLC and NMR. Using AG-P-I as substrate, purified PoGal3 exhibited an optimal pH of 5.0 and temperature of 40°C. We also discovered that Zn2+ had the strongest promoting effect on enzyme activity, increasing it by 28.6%. Substrate specificity suggests that PoGal3 functions as an exo-ß-1,3-galactanase, with its greatest catalytic activity observed on AG-P-I. Hydrolytic products of AG-P-I are mainly composed of galactose and ß-1,6-galactobiose. In addition, PoGal3 can catalyze hydrolysis of LWAG to produce galacto-oligomers. PoGal3 is the first enzyme identified as an exo-ß-1,3-galactanase that can be used in building glycan blocks of crucial glycoconjugates to assess their biological functions.

Cloning, Expression, and Characterization of Endo-ß-1,6-galactanase PoGal30 from Penicillium oxalicum.

Because ß-1,6-galactans are significant components in arabinogalactans from plant cell walls, identifying selective endo-ß-1,6-galactanases is crucial to degrading these polysaccharides and to analyzing and modifying their structures. Here, we cloned and expressed in E. coli a novel endo-ß-1,6-galactanase in the glycosidic hydrolase family 30 (GH30) from Penicillium oxalicum. Our recombinant PoGal30 hydrolase (1464 bp gene) that contains an N-terminal His-tag for purification by nickel affinity chromatography has a specific activity of 3.8 U/mg on the substrate de-arabinosylated gum Arabic (dGA) polysaccharide. The enzyme has 487 residues with a molecular mass of 60 kDa, an isoelectric point of 6, and functional pH and temperature optima of pH 2.5 to pH 5.0 and 40 °C, respectively. While the activity of PoGal30 is activated by Mg2+ (5 or 50 mmol/L), it is completely inhibited by Cu2+ and Fe3+ (50 mmol/L) and partially inhibited by Hg2+, EDTA, and SDS (50 mmol/L). The enzyme demonstrates high specificity towards ß-1,6-galactosidic linkages in dGA, but is inactive against aryl-glycosides and galactobioses with different linkages. Using PoGal30 is, therefore, an effective approach to analyzing the fine structure of polysaccharides and preparing bioactive oligosaccharides.

Cloning and expression of a novel α-1,3-arabinofuranosidase from Penicillium oxalicum sp. 68.

The discovery and creation of biocatalysts for plant biomass conversion are essential for industrial demand and scientific research of the plant cell wall. α-1,2 and α-1,3-L-arabinofuranosidases are debranching enzymes that catalyzing hydrolytic release of α-L-arabinofuranosyl residues in plant cell wall. Gene database analyses shows that GH62 family only contains specific α-L-arabinofuranosidases that play an important role in the degradation and structure of the plant cell wall. At present, there are only 22 enzymes in this group has been characterized. In this study, we cloned a novel α-1,3-arabinofuranosidase gene (poabf62a) belonging to glycoside hydrolase family 62 from Penicillium oxalicum sp. 68 and expressed it in Pichia pastoris. The molecular mass of recombinant PoAbf62A was estimated to be 32.9 kDa. Using p-nitrophenyl-α-l-arabinofuranoside (pNPαAbf) as substrate, purified PoAbf62A exhibited an optimal pH of 4.5 and temperature of 35 °C. Results of methylation and 13C NMR analyses showed that PoAbf62A was exclusively α-1,3-arabinofuranosidase, specific for cleavage of α-1,3-arabinofuranosyl residues, and with the absence of activity towards α-1,2-arabinofuranose and α-1,5-arabinofuranose. Therefore, PoAbf62A exhibits high activity on sugar beet arabinan and wheat arabinoxylan, because their branched side chain are decorated with α-1,3-arabinofuranose. On the other hand, there is a lack of activity with linear-α-L-1,5-arabinan and xylan that only contained α-L-1,5-arabinofuranose or ß-1,4-xylose. The α-1,3-arabinofuranosidase activity identified here provides a new biocatalytic tool to degrade hemicellulose and analyze the structure of plant cell walls.