Abstract
As is well-known, endo-1,4-β-xylanase and β-xylosidase are the rate-limiting enzymes in the degradation of xylan (the major hemicellulosic component), main functions of which are cleavaging xylan to release xylooligosaccharides (XOS) and xylose that these two compounds have important application value in fuel, food, and other industries. This study focuses on enzymatic hydrolysis of poplar sawdust xylan for production of XOS and xylose by a GH11 endo-1,4-β-xylanase MxynB-8 and a GH39 β-xylosidase Xln-DT. MxynB-8 showed excellent ability to hydrolyze hemicellulose of broadleaf plants, such as poplar. Under optimized conditions (50°C, pH 6.0, dosage of 500 U/g, substrate concentration of 2 mg/mL), the final XOS yield was 85.5%, and the content of XOS2−3 reached 93.9% after 18 h. The enzymatic efficiency by MxynB-8 based on the poplar sawdust xylan in the raw material was 30.5%. Xln-DT showed excellent xylose/glucose/arabinose tolerance, which is applied as a candidate to apply in degradation of hemicellulose. In addition, the process and enzymatic mode of poplar sawdust xylan with MxynB-8 and Xln-DT were investigated. The results showed that the enzymatic hydrolysis yield of poplar sawdust xylan was improved by adding Xln-DT, and a xylose-rich hydrolysate could be obtained at high purity, with the xylose yield of 89.9%. The enzymatic hydrolysis yield was higher (32.2%) by using MxynB-8 and Xln-DT together. This study provides a deep understanding of double-enzyme synergetic enzymolysis of wood polysaccharides to valuable products.
Highlights
Hemicellulose is a structural polysaccharide that constitutes agricultural and forestry plant cell wall, which is often cross-linked with cellulose and lignin to form lignocellulose (Yang et al, 2020)
Under the optimal culture conditions, the endo-1,4-β-xylanases MxynB-8 and XynB-DT belonging to GH11 were heterologously expressed in E. coli BL21 (DE3) after incubation with 0.1 mM IPTG for 6 h, whereas the β-xylosidase Xln-DT belonging to GH39 and Dt-xyl3 belonging to GH3 were heterologously expressed in E. coli BL21 (DE3) after incubation with 0.01 mM IPTG for 14 h
The purified endo-1,4-β-xylanase MxynB-8/XynB-DT and β-xylosidase Xln-DT/Dt-xyl3 showed a single band on the SDS-PAGE gel and a molecular mass of ∼24, 50, 55, and 80 kDa, respectively, without undesired bands (Figure 1)
Summary
Hemicellulose is a structural polysaccharide that constitutes agricultural and forestry plant cell wall, which is often cross-linked with cellulose and lignin to form lignocellulose (Yang et al, 2020). The. Co-production of Xylooligosaccharides and Xylose side chain may contain a small amount of glucuronic acid (D-glucuronic acid, 4-O-methyl-D-glucuronic acid, and D-galacturonic acid) groups (Sun et al, 2013). With the processing and utilization of poplar wood resources, a large number of wood residues and sawdust have been produced. These poplar sawdust residues contain 20– 35% hemicellulose, which xylosyl group accounted for 30–40% of total sugar (Yan et al, 2015). Poplar sawdust has become one of the potential raw materials for efficient utilization of hemicellulose
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