Secretory Expression, Functional Characterization, and Molecular Genetic Analysis of Novel Halo-Solvent-Tolerant Protease from Bacillus gibsonii

A novel protease gene from Bacillus gibsonii, aprBG, was cloned, expressed in B. subtilis, and characterized. High-level expression of aprBG was achieved in the recombinant strain when a junction was present between the promoter and the target gene. The purified recombinant enzyme exhibited similar N-terminal sequences and catalytic properties to the native enzyme, including high affinity and hydrolytic efficiency toward various substrates and a superior performance when exposed to various metal ions, surfactants, oxidants, and commercial detergents. AprBG was remarkably stable in 50% organic solvents and retained 100% activity and stability in 0-4 M NaCl, which is better than the characteristics of previously reported proteases. AprBG was most closely related to the high-alkaline proteases of the subtilisin family with a 57-68% identity. The secretion and maturation mechanism of AprBG was dependent on the enzyme activity, as analyzed by site-directed mutagenesis. Thus, when taken together, the results revealed that the halo-solvent-tolerant protease AprBG displays significant activity and stability under various extreme conditions, indicating its potential for use in many biotechnology applications.