Characterization of a Glucose-, Xylose-, Sucrose-, and d-Galactose-Stimulated β-Glucosidase from the Alkalophilic Bacterium Bacillus halodurans C-125

The gene (Bhbgl) encoding a beta-glucosidase from the alkalophilic bacterium Bacillus halodurans C-125 was synthesized chemically via the PCR-based two-step DNA synthesis (PTDS) method and expressed in Escherichia coli. Bhbgl contained an open reading frame (ORF) of 1359 bp encoding a 453-amino acid protein belonging to glycoside hydrolase family 1 (GHF1), and the deduced molecular mass of recombinant Bhbgl (52,488 Da) was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The enzyme exhibited a high specific activity with o-nitrophenyl-beta-d-glucopyranoside (oNPGlu) and an apparent K (m) value of 0.32 mM. With oNPGlu as the substrate, Bhbgl displayed pH and temperature optima of similar to 7.0 and 50A degrees C, respectively. The enzyme was relatively stable under alkaline conditions and > 50% activity was retained after incubation at pH 9.5 for 24 h at 4A degrees C. Recombinant Bhbgl activity was inhibited by 5 mM Zn2+, Fe3+, or Cd2+, but was enhanced by 1 mM Mg2+ and other metal ions. Enzyme activity was also stimulated by at least four sugars (sucrose, d-galactose, xylose, glucose) at concentrations ranging from 50 to 800 mM.