Improvement of alkaliphily of thermostable GH family 10 xylanase from Thermotoga maritima by directed evolution

Xylanase B (XynTB) from hyperthermophilic bacterium Thermotoga maritima MSB8 is a thermostable xylanase classified into glycoside hydrolase family 10. XynTB is most active at pH 6.0, and shows lower activity at alkaline pHs. Improvement of alkaliphily of XynTB was attempted by directed evolution. One mutant enzyme that showed slightly higher activity under high temperature and alkaline pH conditions was acquired from a newly constructed random mutant library. Protein engineering study of this mutant revealed that the amino acid substitution N92D (Asn92 was substituted by Asp) could contribute to the improvement of alkaliphily.