Isolation of a Novel Cold-Active Family 11 Xylanase from the Filamentous Fungus Bispora antennata and Deletion of its N-Terminal Amino Acids on Thermostability

In the present study, we first reported a cold-active xylanase of glycosyl hydrolase family 11, Xyn11, from the filamentous fungus Bispora antennata. The coding gene (xyn11) was cloned and successfully expressed in Pichia pastoris. Deduced Xyn11 exhibited the highest identity of 65 % with a family 11 endo-beta-1,4-xylanase from Alternaria sp. HB186. Recombinant Xyn11 exhibited maximal activity at 35 A degrees C and remained 21 % of the activity at 0 A degrees C. Sequence alignment showed that the N-terminal sequence of Xyn11 is distinct from those of thermophilic xylanases of family 11. To determine its effect on enzyme properties, the Xyn11 mutant without the N-terminal sequence, t-Xyn11, was then constructed, expressed in P. pastoris, and compared with Xyn11. Both enzymes showed optimal activities at 35 A degrees C and pH 5.5 and were stable at pH 2.0-12.0. Compared with truncated mutant t-Xyn11, Xyn11 retained more activity after 20-min incubation at 40 A degrees C (Xyn11:28 % vs. t-Xyn11:4 %) and degraded xylan substrates more completely. Thus, a new factor affecting the thermostability of cold-active xylanase of family 11 was identified.