Starch is comprised of very large α-glucan molecules composed primarily of linear amylose and highly branched amylopectin. Most methods for analyses of starch structure use hydrolytic enzymes to cleave starch. When undegraded, whole starch structures can be analyzed by gel-permeation chromatography (GPC), but this typically yields a single peak each for amylopectin and amylose. The objective of this study was to stably separate amylopectins in whole starch based on their molecular weight using GPC, and to determine the structure of each peak. When alkali-gelatinized whole starch was applied to GPC columns (Toyopearl HW75S×2, HW65S and HW55S), it was separated into three peaks. Iodine staining and chain length distribution analyses of debranched samples showed that peaks were mainly composed of high-molecular weight (MW) amylopectin consisting of many clusters, low-MW amylopectin consisting of a small number of clusters, and amylose.
Woody biomass is anticipated to be a resource for a decarbonized society, but the difficulty of isolating woody components is a significant challenge. Brown-rot fungi, a type of wood rotting fungi, decompose hemicellulose particularly efficiently. However, there are few reports on the hemicellulases from brown-rot fungi. An α-L-arabinofuranosidase belonging to glycoside hydrolase family 51 (GH51) from the brown-rot fungus Gloeophyllum trabeum (GtAbf51A) was cloned and characterized in the present study. Analyses of the phylogeny of GH51 enzymes in wood rotting fungi revealed the existence of two groups, intercellular and extracellular enzymes. After deglycosylation, the recombinant GtAbf51A produced by Pichia pastoris appeared on SDS-PAGE as approximately 71,777 daltons, which is the expected molecular weight based on the amino acid sequence of GtAbf51A. Maximum enzyme activity occurred between pH 2.2 and 4.0 and at 50°C, while it was stable between pH 2.2 and 10.0 and up to 40°C. Due to the presence of a signal peptide, GtAbf51A was thought to hydrolyze polysaccharide containing arabinose. However, the hydrolysis rate of arabinosyl linkages in polysaccharides was only 3%–4% for arabinoxylan and 17% for arabinan. GtAbf51A, in contrast, efficiently hydrolyzed arabinoxylooligosaccharides, particularly O-α-L-arabinofuranosyl-(1→3)-O-β-D-xylopyranosyl-(1→4)-β-Dxylopyranose, which is the principal product of GH10 β-xylanase. These data suggest that GtAbf51A cooperates with other xylan-degrading enzymes, such as β-xylanase, to degrade xylan in nature.
Dextran α-1,2-debranching enzyme (DDE) releases glucose with hydrolyzing α-(1→2)-glucosidic linkages in α-glucans, which are made up of dextran with α-(1→2)-branches and are generated by Leuconostoc bacteria. DDE was isolated from Microbacterium dextranolyticum (formerly known as Flavobacterium sp. M-73) 40 years ago, although the amino acid sequence of the enzyme has not been determined. Herein, we found a gene for this enzyme based on the partial amino acid sequences from native DDE and characterized the recombinant enzyme. DDE had a signal peptide, a glycoside hydrolase family 65 domain, a carbohydrate-binding module family 35 domain, a domain (D-domain) similar to the C-terminal domain of Arthrobacter globiformis glucodextranase, and a transmembrane region at the C-terminus. Recombinant DDE released glucose from α-(1→2)-branched α-glucans produced by Leuconostoc citreum strains B-1299, S-32, and S-64 and showed weak hydrolytic activity with kojibiose and kojitriose. No activity was detected for commercial dextran and Leuconostoc citreum B-1355 α-glucan, which do not contain α-(1→2)-linkages. The removal of the D-domain decreased the affinity for α-(1→2)-branched α-glucans but not for kojioligosaccharides, suggesting that D-domain plays a role in α-glucan binding. Genes for putative dextranases, oligo-1,6-glucosidase, sugar-binding protein, and permease were present in the vicinity of the DDE gene, and as a result these gene products may be necessary for the use of α-(1→2)-branched glucans. Our findings shed new light on how actinobacteria utilize polysaccharides produced by lactic acid bacteria.
Lytic polysaccharide monooxygenases (LPMO) are key enzymes for the efficient degradation of lignocellulose biomass with cellulases. A lignocellulose-degradative strain, Paenibacillus xylaniclasticus TW1, has LPMO-encoding PxAA10A gene. Neither the C1/C4-oxidizing selectivity nor the enzyme activity of PxAA10A has ever been characterized. In this study, the C1/C4-oxidizing selectivity of PxAA10A and the boosting effect for cellulose degradation with a cellulase cocktail were investigated. The full-length PxAA10A (rPxAA10A) and the catalytic domain (rPxAA10A-CD) were heterologously expressed in Escherichia coli and purified. To identify the C1/C4- oxidizing selectivity of PxAA10A, cellohexaose was used as a substrate with the use of rPxAA10A-CD, and the products were analyzed by MALDI-TOF/MS. As a result, aldonic acid cellotetraose and cellotetraose, the products from C1-oxidization and C4- oxidization, respectively, were detected. These results indicate that PxAA10A is a 1/C4- oxidizing LPMO. It was also found that the addition of rPxAA10A into a cellulase cocktail enhanced the cellulose-degradation efficiency.
We created a Microsoft Excel file, Enzyme_Kinetics_Calculator, which includes macro programs that automatically calculates kinetic parameters for typical kinetic equations of enzymatic reactions, accompanied by their standard errors, by minimizing the residual sum of squares thereof. The [S]–v plot is automatically drawn with the theoretical lines and, similarly, the 1/[S]-1/v plot in the case of linear theoretical lines. Enzyme_Kinetics_Calculator is available as a supplementary file for this paper (see J. Appl. Glycosci. Web site).
Algal sulfated polysaccharides are known to be effective hyaluronidase inhibitors. We evaluated hyaluronidase inhibitory activity of sulfated polysaccharide (SP) from Caulerpa lentillifera. Results showed that SP with IC50 of 163 μg/mL appears to allosterically inhibit the hyaluronidase activity. Main sugar composition and sulfate content of SP was estimated to be Gal, Glc, Xyl, Man, uronic acids and sulfate in the weight percent of 27.7: 28.9: 14.6: 22.5: 3.4: 21.7. We modified the SP by desulfation and partial hydrolysis with trifluoroacetic acid (TFA) to investigate the effect of sulfate content and molecular weight on inhibition. Hyaluronidase inhibitory activity of desulfated SP, 0.1 M TFA-hydrolyzed SP and 0.5 M TFA-hydrolyzed SP were significantly lower than that of native SP, revealing that sulfate content or molecular weight is important for hyaluronidase inhibition.