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KMID : 0545120150250010011
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Journal of Microbiology and Biotechnology
2015 Volume.25 No. 1 p.11 ~ p.17
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Improvement of the Optimum pH of Aspergillus niger Xylanase towards an Alkaline pH by Site-Directed Mutagenesis
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Fei Li
Jingcong Xie
Xuesong Zhang
Linguo Zhao
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Abstract
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In an attempt to shift the optimal pH of the xylanase B (XynB) from Aspergillus niger towards alkalinity, target mutation sites were selected by alignment between Aspergillus niger xylanase B and other xylanases that have alkalophilic pH optima that highlight charged residues in the eight-residues-longer loop in the alkalophilic xylanase. Multiple engineered XynB mutants were created by site-directed mutagenesis with substitutions Q164K and Q164K+D117N. The variant XynB-117 had the highest optimum pH (at 5.5), which corresponded to a basic 0.5 pH unit shift when compared with the wild-type enzyme. However, the optimal pH of the XynB- 164 mutation was not changed, similar to the wild type. These results suggest that the residues at positions 164 and 117 in the eight-residues-longer loop and the cleft’s edge are important in determining the pH optima of XynB from Aspergillus niger.
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KEYWORD
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xylanase B, Aspergillus niger, alkaline, site-directed mutagenesis
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