Heterologous Expression and Characterization of an Acidic GH11 Family Xylanase from Hypocrea orientalis

A gene encoding glycoside hydrolase family 11 xylanase (HoXyn11B) from Hypocrea orientalis EU7-22 was expressed in Pichia pastoris with a high activity (413 IU/ml). HoXyn11B was partly N-glycosylated and appeared two protein bands (19-29 kDa) on SDS-PAGE. The recombinant enzyme exhibited optimal activity at pH 4.5 and 55 A degrees C, and retained more than 90% of the original activity after incubation at 50 A degrees C for 60 min. The determined apparent K (m) and V (max) values using beechwood xylan were 10.43 mg/ml and 3246.75 IU/mg, respectively. The modes of action of recombinant HoXyn11B on xylo-oligosaccharides (XOSs) and beechwood xylan were investigated by thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), which indicated that the modes of action of HoXyn11B are different from HoXyn11A since it is able to release a significant amount of xylose from various substrates. This study provides an opportunity to better understand the hydrolysis mechanisms of xylan by xylanases from Trichoderma.