Biochemical characterization of a xylose-tolerant GH43 beta-xylosidase from Geobacillus thermodenitrificans

Hemicelluloses are the second most abundant polysaccharide in plant biomass, in which xylan is the main constituent. Aiming at the total degradation of xylan and the obtention of fermentable sugars, several enzymes acting synergistically are required, especially beta-xylosidases. In this study, beta-xylosidase from Geobacillus thermodenitrificans (GtXyl) was expressed in E. coli BL21 and characterized. The enzyme GtXyl has been grouped within the family of glycoside hydrolases 43 (GH43). Results showed that GtXyl obtained the highest activity at pH 5.0 and temperature of 60 C-degrees. In the additive's tests, the enzyme remained stable in the presence of metal ions and EDTA, and showed high tolerance to xylose, with a relative activity of 55.4% at 400 mM. The enzyme also presented bifunctional activity of beta-xylosidase and alpha-L-arabinofuranosidase, with the highest activity on the substrate p-nitrophenyl-beta-D-xylopyranoside. The specific activity on p-nitrophenyl-beta-D-xylopyranoside was 18.33 U mg(- 1) and catalytic efficiency of 20.21 mM(-1) s(- 1), which is comparable to other beta-xylosidases reported in the literature. Putting together, the GtXyl enzyme presented interesting biochemical characteristics that are desirable for the application in the enzymatic hydrolysis of plant biomass, such as activity at higher temperatures, high thermostability and stability to metal ions.

Automated summary

In this study, a beta-xylosidase from Geobacillus thermodenitrificans (GtXyl) was expressed and characterized. The enzyme showed the highest activity at pH 5.0 and a temperature of 60°C. It exhibited stability in the presence of metal ions and xylose, and also presented bifunctional activity of beta-xylosidase and alpha-L-arabinofuranosidase.