Purification and characterization of arabinofuranosidase from the corn endophyte Acremonium zeae

Acremonium zeae, one of the most prevalent fungal colonists of preharvest corn, possesses a suite of hemicellulolytic activities including xylanase, xylosidase, and arabinofuranosidase. Two enzymes with arabinofuranosidase activity were purified from cell-free culture supernatants of A. zeae grown on oat spelt xylan. A 47 kDa enzyme (AF47) was optimally active at 37 degrees C and pH 6.0, and had a specific activity for 4-nitrophenyl-alpha-L-arabinofuranoside (4NPA) of 6.2 U/mg. A 30 kDa enzyme (AF30) was optimally active at 50 degrees C and pH 4.5, and had a specific activity for 4NPA of 12.4 U/mg. AF47 hydrolyzed 4-nitrophenyl-beta-D-xylopyranoside, 4-nitrophenyl-beta-D-glucopyranoside, and 4-nitrophenyl-beta-D-cellobioside, as well as producing reducing sugars from corn fiber, wheat, and oat spelt arabinoxylan. AF30 had little detectable activity on the 4-nitrophenyl substrates, except for 4NPA, but activity on arabinoxylans from corn fiber, wheat, and oat spelt was at least 7-fold higher than AF47, with specific activities of 109, 358, and 153 U/mg, respectively. A combination of the two enzymes released 61 and 88% of the total arabinose from corn fiber and wheat arabinoxylans. The arabinofuranosidases produced by A. zeae may have industrial application for the enzymatic hydrolysis of recalcitrant lignocellulosic feedstocks such as corn fiber and wheat straw.