Abstract
The xylanases with high specific activity and resistance to harsh conditions are of high practical value for biomass utilization. In the present study, two new GH11 xylanase genes, MYCTH_56237 and MYCTH_49824, have been cloned from thermophilic fungus Myceliophthora thermophila and expressed in Pichia pastoris. The specific activities of purified xylanases reach approximately 1,533.7 and 1,412.5 U/mg, respectively. Based on multiple template-based homology modeling, the structures of their catalytic domains are predicted. Enzyme activity was more effective in 7.5 L fermentor, yielding 2,010.4 and 2,004.2 U/mL, respectively. Both enzymes exhibit optimal activity at 60°C with pH of 6.0 and 7.0, respectively. Their activities are not affected by EDTA and an array of metal ions. The kinetic constants have been determined for MYCTH_56237 (Km = 8.80 mg/mL, Vmax = 2,380 U/mg) and MYCTH_49824 (Km = 5.67 mg/mL, Vmax = 1,750 U/mg). More importantly, both xylanases significantly cooperate with the commercial cellulase Celluclast 1.5 L in terms of the saccharification efficiency. All these biochemical properties of the xylanases offer practical potential for future applications.
Highlights
Plant biomass needs to be explored as a significant source of components that can be converted into products used in industrial processing
The present study describes the cloning and expression of two novel xylanase-encoding genes from M. thermophila belonging to family GH11, with their heterologous expression using the methylotrophic yeast P. pastoris expression system
Yeast extract peptone dextrose (YPD) and buffered minimal glycerol (BMGY) media were used for the cultivation of P. pastoris
Summary
Plant biomass needs to be explored as a significant source of components that can be converted into products used in industrial processing. It is the most abundant renewable source of energy and mainly consists of lignocellulose, the complicated heterogeneous complex made up of hemicellulose, lignin and cellulose (Tuck et al, 2012). The major component of hemicellulose, xylan, has a high capability for conversion to applicable products. Xylanases play a vital role in the efficient saccharification of lignocellulose materials and are of great interest for their capability to hydrolyze biomass to fermentable sugars (Zhang et al, 2011). Various strategies have been applied to reduce the cost, such as improving enzyme activity, using crude extract enzymes or enzyme cocktails and maximizing enzyme production (Del Pozo et al, 2012; Lin et al, 2017)
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