Reconstitution of a thermostable xylan-degrading enzyme mixture from the bacterium Caldicellulosiruptor bescii.

ABSTRACT: Xylose, the major constituent of xylans, as well as the side chain sugars, such as arabinose, can be metabolized by engineered yeasts into ethanol. Therefore, xylan-degrading enzymes that efficiently hydrolyze xylans will add value to cellulases used in hydrolysis of plant cell wall polysaccharides for conversion to biofuels. Heterogeneous xylan is a complex substrate, and it requires multiple enzymes to release its constituent sugars. However, the components of xylan-degrading enzymes are often individually characterized, leading to a dearth of research that analyzes synergistic actions of the components of xylan-degrading enzymes. In the present report, six genes predicted to encode components of the xylan-degrading enzymes of the thermophilic bacterium Caldicellulosiruptor bescii were expressed in Escherichia coli, and the recombinant proteins were investigated as individual enzymes and also as a xylan-degrading enzyme cocktail. Most of the component enzymes of the xylan-degrading enzyme mixture had similar optimal pH (5.5 to ?6.5) and temperature (75 to ?90°C), and this facilitated their investigation as an enzyme cocktail for deconstruction of xylans. The core enzymes (two endoxylanases and a ?-xylosidase) exhibited high turnover numbers during catalysis, with the two endoxylanases yielding estimated k(cat) values of ?8,000 and ?4,500 s(-1), respectively, on soluble wheat arabinoxylan. Addition of side chain-cleaving enzymes to the core enzymes increased depolymerization of a more complex model substrate, oat spelt xylan. The C. bescii xylan-degrading enzyme mixture effectively hydrolyzes xylan at 65 to 80°C and can serve as a basal mixture for deconstruction of xylans in bioenergy feedstock at high temperatures.

SUBMITTER: Su X 

PROVIDER: S-EPMC3591937 | biostudies-literature | 2013 Mar

REPOSITORIES: biostudies-literature