Expression of A Thermostable Xylanase Gene in Pichia pastoris and Its Enzymatic Characterization

A codon-optimized gene encoding a hyperthermostable xylanase belongs to the glycoside hydrolase family 11 (abbreviated as Syxyn11) has been cloned into the expression plasmid pPIC9K (named pPIC9K-Syxyn11). The pPIC9K-Syxyn11 was linearized with SalⅠ and integrated into the genome of Pichia pastoris GS115 by electroporation. The recombinant P. pastoris GS115/Syxyn11 was screened by G418 and then was induced with methanol to express SyXyn11. The SyXyn11 activity expressed by P. pastoris transformant reached 17.74 U/mL. The molecular weight of SyXyn11 was estimated to be 31 000 by SDS-PAGE. The SyXyn11 displayed the highest activity at 85 ℃and pH 6.5. It was highly stable at a temperature of 80 ℃ or below,and at a pH range of 5.0~ 7.5. Its activity was not significantly affected by most of metal ions tested and EDTA. This revealed that Syxyn11 was successfully expressed in P. pastoris and remained the high thermostability.