Ovomucin, a hen egg white protein, is characterized by its hydrogel-forming properties, high molecular weight, and extensive O-glycosylation with a high degree of sialylation. As a commonly used food ingredient, we explored whether ovomucin has an effect on the gut microbiota. O-Glycan analysis revealed that ovomucin contained core-1 and 2 structures with heavy modification by N-acetylneuraminic acid and/or sulfate groups. Of the two mucin-degrading gut microbes we tested, Akkermansia muciniphila grew in medium containing ovomucin as a sole carbon source during a 24 h culture period, whereas Bifidobacterium bifidum did not. Both gut microbes, however, degraded ovomucin O-glycans and released monosaccharides into the culture supernatants in a species-dependent manner, as revealed by semi-quantified mass spectrometric analysis and anion exchange chromatography analysis. Our data suggest that ovomucin potentially affects the gut microbiota through O-glycan decomposition by gut microbes and degradant sugar sharing within the community.
According to whole-genome sequencing, Aspergillus niger produces multiple enzymes of glycoside hydrolases (GH) 31. Here we focus on a GH31 α-glucosidase, AgdB, from A. niger. AgdB has also previously been reported as being expressed in the yeast species, Pichia pastoris; while the recombinant enzyme (rAgdB) has been shown to catalyze tranglycosylation via a complex mechanism. We constructed an expression system for A. niger AgdB using Aspergillus nidulans. To better elucidate the complicated mechanism employed by AgdB for transglucosylation, we also established a method to quantify glucosidic linkages in the transglucosylation products using 2D NMR spectroscopy. Results from the enzyme activity analysis indicated that the optimum temperature was 65 °C and optimum pH range was 6.0–7.0. Further, the NMR results showed that when maltose or maltopentaose served as the substrate, α-1,2-, α-1,3-, and small amount of α-1,1-β-linked oligosaccharides are present throughout the transglucosylation products of AgdB. These results suggest that AgdB is an α-glucosidase that serves as a transglucosylase capable of effectively producing oligosaccharides with α-1,2-, α-1,3-glucosidic linkages.
Cellobiose dehydrogenase (CDH) is a flavocytochrome catalyzing oxidation of the reducing end of cellobiose and cellooligosaccharides, and has a key role in the degradation of cellulosic biomass by filamentous fungi. Here, we use a lineup of glucose/xylose-mixed β-1,4-linked disaccharides and trisaccharides, enzymatically synthesized by means of the reverse reaction of cellobiose phosphorylase and cellodextrin phosphorylase, to investigate the substrate recognition of CDH. We found that CDH utilizes β-D-xylopyranosyl-(1→4)-D-glucopyranose (Xyl-Glc) as an electron donor with similar Km and kcat values to cellobiose. β-D-Glucopyranosyl-(1→4)-D-xylopyranose (Glc-Xyl) shows a higher Km value, while xylobiose does not serve as a substrate. Trisaccharides show similar behavior; i.e., trisaccharides with cellobiose and Xyl-Glc units at the reducing end show similar kinetics, while the enzyme was less active towards those with Glc-Xyl, and inactive towards those with xylobiose. We also use docking simulation to evaluate substrate recognition of the disaccharides, and we discuss possible molecular mechanisms of substrate recognition by CDH.
The aim of this study was to investigate the effect of pH control by CO2 pressurization on the enzymatic hydrolysis of herbaceous feedstock in the calcium capturing by carbonation (CaCCO) process for fermentable sugar production. The pH of the slurry of 5 % (w/w) Ca(OH)2-pretreated/CO2-neutralized rice straw could be controlled between 5.70 and 6.38 at 50 °C by changing the CO2 partial pressure (pCO2) from 0.1 to 1.0 MPa. A mixture of fungal enzyme preparations, namely, Trichoderma reesei cellulases/hemicellulases and Aspergillus niger β-glucosidase, indicated that pH 5.5–6.0 is optimal for solubilizing sugars from Ca(OH)2-pretreated rice straw. Enzymatic saccharification of pretreated rice straw under various pCO2 conditions revealed that the highest soluble sugar yields were obtained at pCO2 0.4 MPa and over, which is consistent with the expected pH at the pCO2 without enzymes and demonstrates the effectiveness of pH control by CO2 pressurization.
Human urinary trypsin inhibitor (UTI) is a proteoglycan composed of one core protein covalently linked to one glycosaminoglycan, which is a low sulfated chondroitin 4-sulfate. It is used as an anti-inflammatory medicine based on the protease inhibitory activity of the core protein. However, functions of the chondroitin sulfate have not been clarified. Recently, we succeeded in remodeling the UTI chondroitin sulfate to hyaluronan to create hyaluronan hybrid UTI, without changing the core protein. Here, we investigated the effect of the remodeled chondroitin sulfate on the activities of serine proteases. Native UTI showed stronger protease inhibitory activity than hyaluronan hybrid UTI or hydrolyzed glycosaminoglycan UTI. Chondroitin 4-sulfate chains with a small peptide derived from the native UTI did not show any protease inhibitory activity. These results suggest that the chondroitin sulfate chain linked covalently to core protein enhances protease inhibitor activity of UTI although the chondroitin sulfate chain itself does not.