Expression, homology modeling and enzymatic characterization of a new β-mannanase belonging to glycoside hydrolase family 1 from Enterobacter aerogenes B19

作者：Liu, Siyu; Cui, Tangbing^*; Song, Yan

来源：Microbial Cell Factories, 2020, 19(1): 142.

DOI：10.1186/s12934-020-01399-w

• Enterobacter aerogenes
• beta-mannanase
• CBM
• GH1 family
• Enzymatic characterization

Background: beta-mannanase can hydrolyze beta-1,4 glycosidic bond of mannan by the manner of endoglycosidase to generate mannan-oligosaccharides. Currently, beta-mannanase has been widely applied in food, medicine, textile, paper and petroleum exploitation industries. beta-mannanase is widespread in various organisms, however, microorganisms are the main source of beta-mannanases. Microbial beta-mannanases display wider pH range, temperature range and better thermostability, acid and alkali resistance, and substrate specificity than those from animals and plants. Therefore microbial beta-mannanases are highly valued by researchers. Recombinant bacteria constructed by gene engineering and modified by protein engineering have been widely applied to produce beta-mannanase, which shows more advantages than traditional microbial fermentation in various aspects. @@@ Results: A beta-mannanase gene (Man1E), which encoded 731 amino acid residues, was cloned fromEnterobacter aerogenes. Man1E was classified as Glycoside Hydrolase family 1. The bSiteFinder prediction showed that there were eight essential residues in the catalytic center of Man1E as Trp166, Trp168, Asn229, Glu230, Tyr281, Glu309, Trp341 and Lys374. The catalytic module and carbohydrate binding module (CBM) of Man1E were homologously modeled. Superposition analysis and molecular docking revealed the residues located in the catalytic module of Man1E and the CBM of Man1E. The recombinant enzyme was successfully expressed, purified, and detected about 82.5 kDa by SDS-PAGE. The optimal reaction condition was 55 degrees C and pH 6.5. The enzyme exhibited high stability below 60 degrees C, and in the range of pH 3.5-8.5. The beta-mannanase activity was activated by low concentration of Co2+, Mn2+, Zn2+, Ba(2+)and Ca2+. Man1E showed the highest affinity for Locust bean gum (LBG). The K(m)and V(max)values for LBG were 3.09 +/- 0.16 mg/mL and 909.10 +/- 3.85 mu mol/(mL min), respectively. @@@ Conclusions: A new type of beta-mannanase with high activity fromE. aerogenesis heterologously expressed and characterized. The enzyme belongs to an unreported beta-mannanase family (CH1 family). It displays good pH and temperature features and excellent catalysis capacity for LBG and KGM. This study lays the foundation for future application and molecular modification to improve its catalytic efficiency and substrate specificity.