Biochemical and structural characterization of a novel thermophilic and acidophilic β-mannanase from Aspergillus calidoustus

beta-Mannanases hydrolyze lignocellulosic biomass with the release of mannan oligosaccharides, which are considered as renewable resource in higher plants. Here, we cloned, expressed and characterized a novel endo beta-mannanase (ManAC) from Aspergillus calidoustus. Homology alignment analysis indicated that ManAC belonged to glycosyl hydrolase (GH) 5 family members. The analysis of structural homologous model revealed that five residues, Arg(116), Asn(231), His(305), Tyr(307), and Trp(370), constituted the active site of ManAC. Glu(232) and Glu(340), proton donor and nucleophile, formed the catalytic residues of ManAC. The recombinant ManAC exhibited maximal activity at pH 2.5 and 70 degrees C, and it was acid tolerant at a pH range of 2.0-6.0 and thermostable under 60 degrees C. Meanwhile, the activity of ManAC was not significantly affected by various metal ions, except for Mg2+ and Ag2+. The recombinant ManAC exhibited the highest beta-mannanase activity towards locust bean gum (669.7 U/mg) with the K-m and V-max values of 3.4 mg/mL and 982.4 mu mol/min/mg, respectively. These thermophilic and acidophilicc characteristics is better than most extreme 8-mannanase. As the first reported mannanse from Aspergillus calidoustus (ManAC), these excellent properties of ManAC strongly promote the synthesis of mannooligosaccharides which have potential for food and feed industrial applications.

Automated summary

ManAC is a novel endo beta-mannanase from Aspergillus calidoustus with acidophilic and thermophilic characteristics, showing optimal activity at pH 2.5 and 70 degrees C. The enzyme is not significantly affected by most metal ions, except for Mg2+ and Ag2+, and exhibits highest activity towards locust bean gum.