Xylanase is the key enzyme to degrade xylan that is a major component of hemicellulose. The enzyme has potential industrial applications in the food, feed, paper and flax degumming industries. The use of xylanases becomes more and more important in the paper industry for bleaching purposes. Xylanases used in the pulp bleaching process should be stable and active at high temperature and alkaline pH. Thermophilic and alkalophilic xylanases could be obtained by screening the wild type xylanases or engineering the mesophilic and neutral enzymes. In this paper, we reviewed recent progress of screening of the thermophilic and alkalophilic xylanases, molecular mechanism of thermal and alkaline adaptation and molecular engineering. Future research prospective was also discussed.
Endo-1,4-beta Xylanases ; chemistry ; Enzyme Stability ; Hot Temperature ; Hydrogen-Ion Concentration ; Paper ; Protein Engineering

Thermophilic and alkalophilic xylanases have great potential in the pulp bleaching industry. In order to improve the thermal stability of an alkaline family 11 xylanase Xyn11A-LC, aromatic residues were introduced into the N-terminus of the enzyme by rational design. The mutant increased the optimum temperature by 5 degrees C. The wild type had a half-time of 22 min at 65 degrees C and pH 8.0 (Tris-HCl buffer). Under the same condition, the mutant had the half-time of 106 min. CD spectroscopy revealed that the melting temperature (T(m)) values of the wild type and mutant were 55.3 degrees C and 67.9 degrees C, respectively. These results showed that the introduction of aromatic residues could enhance the thermal stability of Xyn11A-LC.
Endo-1,4-beta Xylanases ; chemistry ; Enzyme Stability ; Hydrogen-Ion Concentration ; Protein Engineering ; Temperature