| Summary: | β-mannanase is one of the key enzymes to hydrolyze hemicellulose. At present, most β-mannanases are not widely applied because of their low enzyme activity and unsuitable enzymatic properties. In this work, a new β-mannanase from <i>Enterobacter aerogenes</i> was studied, which laid the foundation for its further application. Additionally, we will further perform directed evolution of the enzyme to increase its activity, improve its temperature and pH properties to allow it more applications in industry. A new β-mannanase (Man26E) from <i>Enterobacter aerogenes</i> was successfully expressed in <i>Escherichia coli</i>. Man26E showed about 40 kDa on SDS-PAGE gel. The SWISS-MODEL program was used to model the tertiary structure of Man26E, which presented a core (<i>α</i>/β)8-barrel catalytic module. Based on the binding pattern of CjMan26 C, Man26E docking Gal1Man4 was investigated. The catalytic region consisted of a surface containing four solvent-exposed aromatic rings, many hydrophilic and charged residues. Man26E displayed the highest activity at pH 6.0 and 55 °C, and high acid and alkali stability in a wide pH range (pH 4–10) and thermostability from 40 to 50 °C. The enzyme showed the highest activity on locust bean gum, and the <i>K<sub>m</sub></i> and V<sub>max</sub> were 7.16 mg mL<sup>−1</sup> and 508 U mg<sup>−1</sup>, respectively. This is the second β-mannanase reported from <i>Enterobacter aerogenes</i> B19. The β-mannanase displayed high enzyme activity, a relatively high catalytic temperature and a broad range of catalytic pH values. The enzyme catalyzed both polysaccharides and manno-oligosaccharides.
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