title: Improvement of the optimum pH of Aspergillus niger xylanase towards an alkaline pH by site-directed mutagenesis.
abstract: 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.
authors.affiliation: College of Chemical Engineering, Nanjing Forestry University, Nanjing, Jiangsu 210037, P.R. China.
authors.forename: Fei
authors.initials: F
authors.lastname: Li
authors.forename: Jingcong
authors.initials: J
authors.lastname: Xie
authors.forename: Xuesong
authors.initials: X
authors.lastname: Zhang
authors.forename: Linguo
authors.initials: L
authors.lastname: Zhao
mesh_terms: D000595:Amino Acid Sequence; D001234:Aspergillus niger / Q000201:enzymology* / Q000235:genetics*; D043364:Endo-1,4-beta Xylanases / Q000096:biosynthesis / Q000235:genetics* / Q000493:pharmacokinetics*; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
chemical_list: D043364:Endo-1,4-beta Xylanases