Advances and prospection in preparations, bio-actives and applications of functional xylo-oligosaccharide

Synergy of GH67 and GH115 α-1,2-glucuronidases with Penicillium subrubescens endoxylanases to stimulate xylooligosaccharide production

A primary substitution of the plant cell wall hemicellulosic polysaccharide xylan is (4-O-methyl-)d-glucuronic acid, which hinders the endoxylanases (XLNs) degradation of xylan for the production of valuable xylooligosaccharides (XOS). In this context, α-1,2-glucuronidase (AGU) plays a critical role in hydrolyzing the α-(1→2)-glycosidic linkages between 4-O-methyl-d-glucuronic acid and xylosyl residues in xylan, thereby enhancing XOS production by XLNs. However, AGUs have been relatively poorly studied, and insufficient and incomplete data on their biochemical properties, substrate specificity, and product profiling has limited their application. Here, we cloned, heterologously produced, purified and functionally characterized an AGU from Aspergillus niger (AnAguA) and another AGU from Penicillium subrubescens (PsAguB), belonging to Glycoside Hydrolase family 67 (GH67) and 115 (GH115), respectively, in the Carbohydrate-Active enZyme database. Results showed that neither AGU released 4-O-methyl-d-glucuronic acid from polymeric beech wood glucuronoxylan (BeWX). However, we found that from BeWX pre-digested with GH10 or GH11 XLNs from P. subrubescens (PsXlnA and PsXlnF, respectively), AnAguA released 4-O-methyl-d-glucuronic acid only from the non-reducing end of glucuronoxylan oligosaccharide, whereas PsAguB released 4-O-methyl-d-glucuronic acid from glucuronoxylan oligosaccharides regardless of the xylosyl substitution position. Furthermore, we demonstrated that enhancement of XOS release by adding AGUs to various combinations of GH10 (PsXlnA-C) and GH11 (PsXlnD-F, PsXlnH-I) XLNs from P. subrubescens varied based on the AGU-XLN combination. The combination of AnAguA with PsXlnA was the most effective, achieving at least a 3-fold increase in the release of XOS with a degree of polymerization of 5-7 compared to using PsXlnA alone.

Expression and characterization of cold-adapted xylanase Xyl-L in Pichia pastoris for xylooligosaccharide (XOS) preparation

BACKGROUND

Xylan, the second most abundant polysaccharide in plant biomass, requires endoxylanases for its hydrolysis into xylooligosaccharides (XOS). Xylanases have been widely used in industries such as animal feed, bakery, juice production, and paper pulp. Recently, XOS have gained attention for their health benefits, including improved digestion, reduced cholesterol, and antioxidant effects. The cold-adapted GH10 xylanase of Antarctic origin Xyl-L was previously expressed in Escherichia coli, showing promising low-temperature activity. However, Pichia pastoris is currently a preferred host for industrial xylanase production due to its ability to express complex proteins and secrete them into the culture medium. This study explored the expression of Xyl-L in P. pastoris and evaluated its potential for XOS production using common flours as substrates, aiming for applications in the food and nutraceutical industry.

RESULTS

Comparison between AOX1 ( P A O X 1 ) and GAP ( P GAP ) promoters for recombinant Xyl-L production in P. pastoris showed that the P A O X 1 promoter resulted in higher activity per wet-cell weight. Co-transforming P A O X 1 -Xyl strains with plasmids encoding genes aiding in protein folding (HAC1 or PDI1) did not enhance Xyl-L catalytic activity compared to the parental P A O X 1 strain. Thus, P A O X 1 -Xyl was cultivated in 3 L bioreactors in fed-batch cultures; it is presumed that the enzyme is produced with glycosylations within its structure, given its migration within the SDS-PAGE gels. The produced Xyl-L was purified from the culture supernatant, resulting in peak xylanase activity after 90 h, with specific activity of 5.10 ± 0.21 U/mg, at pH 7.5 and 25 ∘ C, using beechwood xylan. It also showed a Km of 3.5 mg/mL and a kcat of 9.16 s - 1 . Xyl-L maintained over 80% of relative activity between pH 5.6 - 8.6 and 37 - 44 ∘ C, and was activated by CaCl 2 and MgCl 2 , but inhibited by MnCl 2 . Xyl-L was tested using several flours (whole wheat, rye, oatmeal and all-purpose) as substrates, where XOS with a polymerization degree (DP) of 2 were obtained from each substrate, whole wheat flour generated XOS with DP 3, and XOS with DP 2, 3 and 4 were produced when beechwood xylan was used as substrate.

CONCLUSIONS

The xylanase Xyl-L was successfully expressed in P. pastoris and proved to be able to degrade various flour substrates, producing XOS with DP ranging from 2 to 4, indicating its potential applications in the nutraceutical and food industries. Further studies must be performed to optimize its production in bioreactors.

Efficient production of xylobiose and xylotriose from xylan in moso bamboo by the combination of pH-controlled lactic acid and xylanase hydrolysis

Short-chain xylo-oligosaccharides (XOS) such as xylobiose (X2) and xylotriose (X3) have higher biological activities. Therefore, it is interesting to produce highly active XOS enriched with X2 and X3. In this work, pH-controlled lactic acid (LA) hydrolysis was used to produce XOS from xylan in moso bamboo and xylanase was used to convert high DP XOS into low DP XOS to increase the percentage of X2 + X3 in XOS. A 33.1 % XOS yield was obtained from 2 % LA hydrolysis (pH = 3.2). After xylanase hydrolysis of the LA hydrolysate, the total XOS yield reached 64.1 %, with X2 + X3 yield reaching 58.4 %. The percentage of X2 + X3 increased from 52.3 % to a high level of 91.0 %. The deep eutectic solvent pretreatment removed 87.2 % lignin from the residue and the glucose yield of the delignified residue hydrolyzed by cellulase was 96.9 %. The results suggested that the integrated process of LA and xylanase hydrolysis could effectively produce X2 + X3 from xylan in moso bamboo.