Biochemical characterization of a novel thermostable β-glucosidase from Dictyoglomus turgidum

Dtur_0462 gene from the hypertermophilic bacterium Dictyoglomus turgidum, encoding a β-glucosidase, was synthetically produced and expressed in Escherichia coli BL21(DE3)-RIL. DturβGlu was purified to homogeneity by affinity chromatography and its homotetrameric structure was determined by gel filtration. The monomer is composed by 418 amino acidic residues and showed high sequence similarity with Glycoside Hydrolases (GHs) belonging to GH1 family. The maximum activity of DturβGlu was observed at 80 °C and at pH 5.4. DturβGlu was stable in the range of pH 5-8 and retained 70% of its activity after 2 h of incubation at 70 °C. Metal ions and chemical reagents differently influenced the β-glucosidase activity; furthermore, DturβGlu displays a good ethanol and glucose tolerance (Ki 750 mM). The enzyme is active on p-nitrophenyl-β-d-glucopyranoside (pNPGlu) (Km 0.84 mM) and p-nitrophenyl-β-d-galactopyranoside (pNPGal) (Km 1.36 mM) and shows a broad substrate specificity towards natural compounds as salicin, cellobiose and genistin. The ability to hydrolyze different substrates, the activation in the presence of surfactants, the good thermal resistance, and finally the high glucose and ethanol tolerance make this enzyme a good candidate for industrial applications.