Purification and characterization of a novel thermophilic β-galactosidase from Picrophilus torridus of potential industrial application

Intracellular β-galactosidase (E.C 3.2.1.23) produced by the thermoacidophilic archeon Picrophilus torridus DSM 9790 was purified to homogeneity using a combination of DEAE Sepharose, gel filtration, hydroxyapatite and chromatofocusing chromatographies. LC–MS/MS analysis was used to confirm the identity of the purified protein. The enzyme was found to be a homotrimer, with a molecular mass of 157.0 kDa and an isoelectric point of 5.7. To our knowledge, this enzyme has the lowest pH optimum of any intracellular β-galactosidase characterized to date. Maximal activity was exhibited at acidic pH values of 5.0–5.5 and at 70 °C. The enzyme retained > 95% activity after heating to 70 °C for 1 h, or after incubation at pH 5.5 for 1 h. The enzyme may be of interest for high-temperature bioprocessing, such as in the production of lactulose. This investigation suggests that the β-galactosidase activity produced by P. torridus is potentially more useful than several enzymes already characterized for such an application.