Construction of whole-cell biocatalyst for xylan degradation through cell-surface xylanase display in Saccharomyces cerevisiae

We constructed a yeast-based whole-cell biocatalyst displaying Trichoderma reesei xylanase II (XYNII) on the cell-surface and endowed the yeast-cells with the ability to degrade xylan. The fusion gene encoding the mature region of XYNII and the C-terminal half (320 amino acid residues from the C-terminal end) of yeast α-agglutinin (XYNII-α-agglutinin) was constructed and expressed in Saccharomyces cerevisiae under the control of a glyceraldehyde-3-phosphate dehydrogenase (GAPDH) promoter. The expression system of fusion gene encoding XYNII-α-agglutinin tagged with RGSHis6 consisting of arginine, glycine, serine, and histidine hexamer (RGSHis6-XYNII-α-agglutinin) was also constructed. Immunofluorescence labeling to confirm cell-surface display of the RGSHis6-XYNII-α-agglutinin fusion protein, and confirmation of similar xylanase activity in yeast-cells expressing XYNII-α-agglutinin and RGSHis6-XYNII-α-agglutinin but not in the culture medium, indicated that XYNII was displayed on the cell-surface in the active form. The XYNII-displaying yeast-based whole-cell biocatalyst showed highest XYNII activity at pH 5.0 and 40 °C, respectively. This whole-cell biocatalyst is expected to find application not only in the first step of fermentation of xylan to ethanol but also in xylooligosaccharide production.