Molecular basis for the increased activity of ZMS-2 serine protease in the presence of metal ions and hydrogen peroxide

Abstract

Serine proteases are important enzymes widely used in commercial products and industry. Recently, we identified a new serine protease from the desert bacterium Bacillus subtilis ZMS-2 that showed enhanced activity in the presence of Zn²⁺, Ag⁺, or H₂O₂. However, the molecular basis underlying this interesting property is unknown. Here, we report comparative studies between the ZMS-2 protease and its homolog, subtilisin E (SubE), from B. subtilis ATCC 6051. In the absence of Zn²⁺, Ag⁺, or H₂O_2, both enzymes showed the same level of proteolytic activity, but in the presence of Zn²⁺, Ag⁺, or H₂O₂, ZMS-2 displayed increased activity by 22%, 8%, and 14%, whereas SubE showed decreased activity by 16%, 12%, and 9%, respectively. In silico studies showed that both proteins have almost identical amino acid sequences and folding structures, except for two amino acids located in the protruding loops of the proteins. ZMS-2 contains Ser236 and Ser268, whereas SubE contains Thr236 and Thr268. Replacing Ser236 or Ser268 in ZMS-2 with threonine resulted in variants whose activities were not enhanced by Zn²⁺ or Ag⁺. However, this single mutation did not affect the enhancement by H₂O₂. This finding may be used as a basis for engineering better proteases for industrial uses.

Keywords: Bacillus subtilis; In silico study; Mutagenesis; Serine protease; Subtilisin E; ZMS-2 protease.