Expression, purification, and characterization of a thermophilic neutral protease from Bacillus stearothermophilus in Bacillus subtilis

The gene coding for a thermophilic neutral protease from Bacillus stearothermophilus was expressed in Bacillus subtilis DB104, under the control of the sacB gene promoter. This was followed by either the native signal peptide sequence of this protease or the signal peptide sequence of the sacB gene. The protease was purified 3.8-fold, with a specific activity of 16530 U mg −1 . As analyzed by SDS-PAGE, the molecular mass of the expressed protease was about 35 kDa, and the optimal temperature and pH of the protease were 65°C and 7.5, respectively. Moreover, it still had about 80% activity after 1 h reaction at 65 °C.