A thermostable alkaliphilic protein-disulfide isomerase from Bacillus subtilis DR8806: cloning, expression, biochemical characterization and molecular dynamics simulation.

Disulfide bonds are among the most important factors related to correct folding of the proteins. Protein disulfide isomerase (PDI) is the enzyme responsible for the correct formation and isomerization of these bonds. It is rarely studied so far and none of them showed industrial properties. In this study, the gene encoding for a putative PDI from Bacillus subtilis DR8806 was identified, cloned and expressed in Escherichia coli. It was encoded a 23.26kDa protein. The enzyme was purified by GST affinity chromatography with a specific activity of 1227u/mg. It was active and stable over a wide range of temperature (20-85°C) and pH (4.5-10) with an optimum at 65°C and pH 5.5. Its activity was enhanced by Mn2+ and Co2+ while Ag+ and Zn2+ decreased it. Some of the known PDI inhibitors such as Tocinoic acid and Bactiracin did not affect its activity. In-silico analysis shows the five amino acids changes in the protein sequence regarding to the consensus sequence of PDIs, have a positive impact toward the protein thermal stability. This was further confirmed by molecular dynamics simulations. By considering the overall results, the enzyme might be a potential candidate for applications in the respective industries.