Expression of an alkalo-tolerant fungal xylanase enhanced by directed evolution in Pichia pastoris and Escherichia coli.
The alkaline stability of the xylanase from Thermomyces lanuginosus was further improved by directed evolution using error-prone PCR mutagenesis. Positive clones were selected by their ability to produce zones of clearing on pH 9 and 12 xylan agar plates. Variant NC38 was able to withstand harsh alkaline conditions retaining 84% activity after exposure at pH 10 for 90 min at 60 degrees C, while the parent enzyme had 22% activity after 60 min. The alkaline stable variant NC38 was cloned into pBGP1 under the control GAP promoter and pET22b(+) for expression in Pichia pastoris and Escherichia coli BL21, respectively. Best extracellular expression of the recombinant xylanase was observed in P. pastoris (261.7+/-0.61 U ml(-1)) whereas intracellular activity was observed in E. coli (47.9+/-0.28 U ml(-1)) was low. Total activity obtained in P. pastoris was 545-fold higher than E. coli. The mutated alkaline stable xylanase from P. pastoris was secreted into the culture medium with little or no contamination by host proteins, which favours the application of this enzyme in the pulp and paper industry.
McHunu
Nokuthula Peace
NP
Department of Biotechnology and Food Technology, Durban University of Technology, Durban, South Africa. nokuthula@dut.ac.za
Singh
Suren
S
Permaul
Kugen
K
D001203:Ascomycota / Q000201:enzymology*; D019020:Directed Molecular Evolution; D043364:Endo-1,4-beta Xylanases / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D006863:Hydrogen-Ion Concentration; D016296:Mutagenesis; D010843:Pichia / Q000235:genetics / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D013696:Temperature
D043364:Endo-1,4-beta Xylanases