Xylanase is an important enzyme in industrial applications, which usually require the enzyme to maintain activity in high-temperature condition. In this study, a GH10 family xylanase XynAFO from a thermophilic composting fungus, Aspergillus fumigatus Z5, was investigated to determine its thermostable mechanism. XynAFO showed excellent thermostability, which could maintain 50% relative activity after incubation for 1 h at 70 degrees C. The homologous modeling structure of XynAFO was constructed and an alpha-helix composed of poly-threonine has been found in the linker region between the catalytic domain and the carbohydrate-binding module domain. Both the molecular dynamics simulation and the biochemical experiments proved that the alpha-helix plays an important role in the thermostability of XynAFO. Introducing of this poly-threonine region to the C-terminus of another GH10 family xylanase improved its thermostability. Our results indicated that the poly-threonine alpha-helix at the C-terminus of the catalytic domain was important for improving the thermophilic of GH10 family xylanases, which provides a new strategy for the thermostability modification of xylanases. (C) 2019 Elsevier Inc. All rights reserved.