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Xyn10D-Fae1A：Bifunctional xylanase/ferulic acid esterase

Xyn10D-fae1A is a bifunctional enzyme, which has the activity of ferulic esterase and xylanase. Feruloyl esterase can hydrolyze ferulic acid ester groups, which are responsible for attaching in complex cellular cell wall structures. Xylanase can hydrolyze plant cell wall component xylan. It can cut the β-1,4 glycosidic bond between the xylose residues in the xylan backbone. This part is responsible for pretreatment of straw.

Sequence and Features

Characterization

Molecular weight

This gene codes for a protein of 726 amino acids with a molecular mass of 82.3 kDa.

Detection of ferulic acid

To detect the expression of Xyn10D-Fae1A gene, we converted carrying Xyn10D-Fae1A gene to co-culture with straw culture medium. Gas chromatography was used to detect ferulic acid. The ferulic acid production was monitored by periodically taking samples from the fermentation liquid of E. coli BL21(DE3) carrying Xyn10D-Fae1A gene. GC results showed that the peak of ferulic acid was appeared after fermentation for 24h with the strain carrying Xyn10D-Fae1A gene, while no ferulic acid was detected in the sample of E. coli BL21(DE3) without vector (Fig. 1).

Fig. 1 The production of ferulic acid determined using GC. The supernatants of fermented liquid of E. coli BL21(DE3) with or without Xyn10D-Fae1A gene were used for the determination of ferulic acid, respectively. Samples were taken from reaction mixtureat 0h, 24h.

The ferulic acid peak was further analyzed by using GC-MS (Fig. 2).

Fig. 2 Mass spectrums of ferulic acid derivative. Sample was the supernatants of E. coli BL21(DE3) carrying Xyn10D-Fae1A gene after fermentation for 24h.

Enzyme activity of xylanase

Fig. 2 Standard Curve of Xylose.

Fig. 3 Xylanase Activity on Xylan. Data were measured inphosphate buffer solution at pH 6.0 and 40℃.

Enzyme activity of xylanase

Ferulic acid esterase can decompose ferulic acid p-nitrophenol ester to produce p-nitrophenol and ferulic acid. The strain BL21 (DE3) transformed with Xyn10D-Fae1A gene was cultivated overnight and centrifuged to obtain the supernatant. The remaining bacteria were broken and broken products were obtained. DSMO solution of ferulic acid p-nitrophenol ester was added to phosphate buffer solution of 630 L pH=6.4 with a concentration of 400 L of 10 mmol/L. Heat preservation 5min at 40℃ and add 0.2ml sample solution. The initial OD values were measured before incubation. Gently mix and incubate 4h at 40 C, determine the final OD value and compare the difference.

Fig. 4 Enzyme Activity of Ferulic acid esterase. Data were measured in phosphate buffer solution at pH 6.4 and 40℃.

The results showed that the ferulic acid enzyme activity of our strain was much higher than that of the wild type.