Isolation and characterization of a thermostable β-xylosidase in the thermophilic bacterium Geobacillus pallidus

Abstract The isolation, purification, biochemical and biophysical characterization of the first reported β-xylosidase from Geobacillus pallidus are described. The protein has an optimum pH close to 8 and an optimum temperature of 70 °C. These biochemical properties agree with those obtained by spectroscopic techniques, namely, circular dichroism (CD), infrared (FTIR) and fluorescence measurements. Thermal denaturation, followed by CD and FTIR, showed an apparent thermal denaturation midpoint close to 80 °C. The protein was probably a hydrated trimer in solution with, an elongated shape, as shown by gel filtration experiments. FTIR deconvolution spectra indicated that the protein contains a high percentage of α-helix (44%) and β-sheet (40%). The sequencing of the N terminus and the biochemical features indicate that this new member of β-xylosidases belongs to the GH52 family. Since there are no reported structural studies of any member of this family, our studies provide the first clue for the full conformational characterization of this protein family.