Abstract
BackgroundXylanase is an important component of hemicellulase enzyme system. Since it plays an important role in the hydrolysis of hemicellulose into xylooligosaccharides (XOs), high thermostable xylanase has been the focus of much recent attention as powerful enzyme as well as in the field of biomass utilization.ResultsA xylanase gene (xyn10A) with 3,474 bp was cloned from the extremely thermophilic bacterium Thermotoga thermarum that encodes a protein containing 1,158 amino acid residues. Based on amino acid sequence homology, hydrophobic cluster and three dimensional structure analyses, it was attested that the xylanase belongs to the glycoside hydrolase (GH) families 10 with five carbohydrate binding domains. When the xylanase gene was cloned and expressed in Escherichia coli BL21 (DE3), the specific enzyme activity of xylanase produced by the recombinant strain was up to 145.8 U mg-1. The xylanase was optimally active at 95°C, pH 7.0. In addition, it exhibited high thermostability over broad range of pH 4.0-8.5 and temperature 55-90°C upon the addition of 5 mM Ca2+. Confirmed by Ion Chromatography System (ICS) analysis, the end products of the hydrolysis of beechwood xylan were xylose, xylobiose, xylotriose, xylotetraose, xylopentaose and xylohexaose.ConclusionsThe xylanase from T. thermarum is one of the hyperthermophilic xylanases that exhibits high thermostability, and thus, is a suitable candidate for generating XOs from cellulosic materials such as agricultural and forestry residues for the uses as prebiotics and precursors for further preparation of furfural and other chemicals.
Highlights
Xylanase is an important component of hemicellulase enzyme system
Through BLAST of the catalytic domain (CD) of Xyn10A on GenBank, it shares the highest similarity of 78% with another xylanase in T. thermarum DSM 5069 (Genbank No YP_004660782)
The recombinant xylanase was purified through a heat treatment at 70C for 30 min followed by a Ni-NTA affinity chromatography
Summary
Xylanase is an important component of hemicellulase enzyme system. Since it plays an important role in the hydrolysis of hemicellulose into xylooligosaccharides (XOs), high thermostable xylanase has been the focus of much recent attention as powerful enzyme as well as in the field of biomass utilization. Compared with other renewable resources, xylans, which are the main constituents of hemicellulose, are the hydrophobic cluster, and three dimensional structural analysis, xylanases are classified mainly into two glycoside hydrolase (GH) families, 10 and 11, which enzyme activities are present in GH 5, 7, 8, 16, 26, 43, 52 and 62 [2,4,8]. The genome sequence of Thermotoga thermarum was reported last year (GenBank accession number: CP002351)
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