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Publication Abstract from PubMed

Background: Improving the hydrolytic performance of hemicellulases to degrade lignocellulosic biomass is of considerable importance for second-generation biorefinery. Xylanase, as the crucial hemicellulase, must be thermostable and have high activity for its potential use in the bioethanol industry. To obtain excellent xylanase candidates, it is necessary to understand the structure-function relationships to provide a meaningful reference to improve the enzyme properties. This study aimed to investigate the catalytic mechanism of a highly active hyperthermophilic xylanase variant, XYL10C-DeltaN, for hemicellulose degradation. Results: By removing the N-terminal 66 amino acids, the variant XYL10C-DeltaN showed a 1.8-fold improvement in catalytic efficiency and could hydrolyze corn stover more efficiently in hydrolysis of corn stover; however, it retained similar thermostability to the wild-type XYL10C. Based on the crystal structures of XYL10C-DeltaN and its complex with xylobiose, Glu175 located on loop 3 was found to be specific to GH10 xylanases and probably accounts for the excellent enzyme properties by interacting with Lys135 and Met137 on loop 2. Site-saturation mutagenesis confirmed that XYL10C-DeltaN with glutamate acid at position 175 had the highest catalytic efficiency, specific activity, and the broadest pH-activity profile. The functional roles of Glu175 were also verified in the mutants of another two GH10 xylanases, XylE and XynE2, which showed increased catalytic efficiencies and wider pH-activity profiles. Conclusions: XYL10C-DeltaN, with excellent thermostability, high catalytic efficiency, and great lignocellulose-degrading capability, is a valuable candidate xylanase for the biofuel industry. The mechanism underlying improved activity of XYN10C-DeltaN was thus investigated through structural analysis and functional verification, and Glu175 was identified to play the key role in the improved catalytic efficiency. This study revealed the importance of a key residue (Glu175) in XYN10C-DeltaN and provides a reference to modify GH10 xylanases for improved catalytic performance.

Insight into the functional roles of Glu175 in the hyperthermostable xylanase XYL10C-DeltaN through structural analysis and site-saturation mutagenesis.,You S, Chen CC, Tu T, Wang X, Ma R, Cai HY, Guo RT, Luo HY, Yao B Biotechnol Biofuels. 2018 Jun 8;11:159. doi: 10.1186/s13068-018-1150-8., eCollection 2018. PMID:29930705^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.