Purification and characterization of a new xylanase with excellent stability from Aspergillus flavus and its application in hydrolyzing pretreated corncobs.

A new extracellular xylanase was purified from a non-toxic mesophilic fungus Aspergillus flavus, and characterized as the β-1, 4-endoxylanase (designated as AfXynA) that appeared in a single protein band on SDS-PAGE with a molecular mass of 20.2 kDa, which is different from all other reported xylanases from the same strain. The AfXynA exhibited a specific activity of 838.2 U/mg. Its optimal temperature and pH were determined to be 55 °C and 7.5, respectively. It was stable up to 50 °C and within pH 3.5-10.5. AfXynA also exhibited an excellent tolerance to various proteases. This new xylanase had an endohydrolytic mode of action and could hydrolyze xylotriose to xylobiose through transglycosylation. It could efficiently degrade xylan to mainly yield xylobiose, xylotriose, xylopentose and xylohexaose. In addition, the AfXynA was effective in hydrolyzing pretreated corncobs, and shows a great potential in the production of xylooligosaccharides. These unique enzymatic properties make the AfXynA attractive for more biotechnological applications.