High-level expression of a hyperthermostable Thermotoga maritima xylanase in Pichia pastoris by codon optimization

The second xylanase gene (xynB) from the hyperthermophilic Thermotoga maritima was optimized according to the codon usage of Pichia pastoris and expressed in P. pastoris. The optimized gene (xynBop) shared 77.8% of nucleotide sequence identity with that of native gene. A total of 232 nucleotides were changed and the G + C ratio was simultaneously increased from 42.7% to 43.1%. The recombinant xylanase (XynBop) was secreted into the culture medium that reached a total extracellular protein concentration of 10.1 g l−1 with an activity of 40,020 U ml−1 in 5-l fermentor culture. The recombinant enzyme was optimally active at pH 5.5 and at 100 °C, respectively. The secreted expression level makes the enzyme a good candidate for hyperthermostable xylanase production.