High-efficiency heterologous expression of nattokinase based on a combinatorial strategy

Nattokinase, traditionally produced by the fermentation of Bacillus natto, has a high-efficiency and safe thrombolytic effect. However, low activity limits its industrial application as a thrombolytic agent. In this study, the nattokinase encoding gene from Bacillus natto was heterologously expressed in B. subtilis WB800 to realize the high-efficiency expression. At first, the gene was amplified and connected to the Escherichia coli-B. subtilis shuttle plasmid pP43NMK to construct the recombinant plasmid pP43NMK-NKF. The enzyme activity increased to 75.3 FU/mL after the signal peptide starting codon was optimized as ATG from GTG. A total of 19 signal peptides were screened to construct a series of recombinants. The recombinant PSP7 showed the highest nattokinase enzyme activity, 235.2 FU/mL. Furthermore, constructing the promoter tandem expression vector proved that the dual-promoter recombinant PSP7C43 has the highest enzyme activity of 247.1 FU/mL. After the optimization of fermentation conditions, the nattokinase enzyme activity of recombinant PSP7C43 finally increased to 325.4 FU/mL. The combinatorial strategy adopted in this study realizes the substantial improvement of nattokinase expression level, which lays a foundation for the industrial development of nattokinase as a thrombolytic reagent.