Biochemical characterization of a GH43 ß-xylosidase from Bacteroides ovatus

Authors: Jordan, Douglas; Stoller, Jeanette; Lee, Charles; Chan, Victor; Wagschal, Kurt

Submitted to: Applied Biochemistry and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/3/2016
Publication Date: 11/16/2016
Citation: Jordan, D.B., Stoller, J.R., Lee, C.C., Chan, V.J., Wagschal, K.C. 2016. Biochemical characterization of a GH43 ß-xylosidase from Bacteroides ovatus. Applied Biochemistry and Biotechnology. 182:250-260. doi: 10.1007/s12010-016-2324-0.
DOI: https://doi.org/10.1007/s12010-016-2324-0

Interpretive Summary: One of our project goals is to identify highly active ß-xylosidases that could perform well in saccharification reactors to help convert hemicelluloses to constituent monomers, which can then be fermented to bioethanol and other valuable products. We identified the highly active ß-xylosidase from Bacteroides ovatus as a good candidate for fulfilling this role. It manifests high activity in the two kinetic parameters of interest: kcat and kcat/Km. The latter parameter of the enzyme is among the highest known. In addition, the value of the inhibition constant for glucose (5 molar) is by far the largest known suggesting that the enzyme should perform well in saccharification reactors that simultaneously convert cellulose and hemicellulose to their monomers, particularly towards the end of the conversions where substrate concentrations would be low and glucose concentrations would be high.

Technical Abstract: Divalent-metal-activated, glycoside hydrolase (GH43) ß-xylosidases have been found to have high kcat/Km for xylooligosaccharides and may demonstrate high efficacy in industrial reactors digesting hemicellulose. By searching an amino acid database, we found an enzyme that is 81% identical in amino acid sequence to a GH43, metal-activated ß-xylosidase with high kcat/Km and also it has 19 of 20 residues in the active site conserved. The GH43 ß-xylosidase has either a tightly-bound metal cofactor or is not activated by metals. At 25°C and pH 6.0, the kcat is 69 s-1 for xylobiose and kcat/Km is 210 s-1mM-1 for xylotriose, the latter being 0.7 that of the highest known value. The determined inhibition constant (Ki) for D-glucose is 4.9 M, the highest known for a ß-xylosidase. The enzyme has potential utility operating in bioreactors digesting plant biomass.