1. High-level expression of a novel thermostable and mannose-tolerant β-mannosidase from Thermotoga thermarum DSM 5069 in Escherichia coli
- Author
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Wenqian Li, Xun Li, Yu Zhang, Yingjuan Huang, Fei Wang, and Hao Shi
- Subjects
DNA, Bacterial ,Bioconversion ,Molecular Sequence Data ,Mannose ,Biology ,Polysaccharide ,medicine.disease_cause ,Substrate Specificity ,Thermotoga thermarum ,Mannose-tolerant ,Mannans ,chemistry.chemical_compound ,Gram-Negative Anaerobic Straight, Curved, and Helical Rods ,Bacterial Proteins ,Polysaccharides ,medicine ,Escherichia coli ,Hemicellulose ,Amino Acid Sequence ,Cloning, Molecular ,Phylogeny ,Mannan ,Thermostability ,Mannooligosaccharides ,chemistry.chemical_classification ,Thermophile ,Temperature ,beta-Mannosidase ,Computational Biology ,Hydrogen-Ion Concentration ,chemistry ,Biochemistry ,β-mannosidase ,Biotechnology ,Research Article ,Half-Life ,Plasmids - Abstract
Background Mannan is one of the primary polysaccharides in hemicellulose and is widely distributed in plants. β-Mannosidase is an important constituent of the mannan-degrading enzyme system and it plays an important role in many industrial applications, such as food, feed and pulp/paper industries as well as the production of second generation bio-fuel. Therefore, the mannose-tolerant β-mannosidase with high catalytic efficiency for bioconversion of mannan has a great potential in the fields as above. Results A β-mannosidase gene (Tth man5) of 1,827 bp was cloned from the extremely thermophilic bacterium Thermotoga thermarum DSM 5069 that encodes a protein containing 608 amino acid residues, and was over-expressed in Escherichia coli BL21 (DE3). The results of phylogenetic analysis, amino acid alignment and biochemical properties indicate that the Tth Man5 is a novel β-mannosidase of glycoside hydrolase family 5. The optimal activity of the Tth Man5 β-mannosidase was obtained at pH 5.5 and 85°C and was stable over a pH range of 5.0 to 8.5 and exhibited 2 h half-life at 90°C. The kinetic parameters K m and V max values for p-nitrophenyl-β-D-mannopyranoside and 1,4-β-D-mannan were 4.36±0.5 mM and 227.27±1.59 μmol min-1 mg-1, 58.34±1.75 mg mL-1 and 285.71±10.86 μmol min-1 mg-1, respectively. The k cat /K m values for p-nitrophenyl-β-D-mannopyranoside and 1,4-β-D-mannan were 441.35±0.04 mM-1 s-1 and 41.47±1.58 s-1 mg-1 mL, respectively. It displayed high tolerance to mannose, with a K i value of approximately 900 mM. Conclusions This work provides a novel and useful β-mannosidase with high mannose tolerance, thermostability and catalytic efficiency, and these characteristics constitute a powerful tool for improving the enzymatic conversion of mannan through synergetic action with other mannan-degrading enzymes.
- Published
- 2013