Cloning, Expression, and Characterization of a Metalloprotease from Thermophilic Bacterium Streptomyces thermovulgaris

Proteases hydrolyze proteins and reduce them to smaller peptides or amino acids. Besides many biological processes, proteases play a crucial in different industrial applications. A 792 bp protease gene (nprB) from the thermophilic bacterium Streptomyces thermovulgaris was cloned and expressed in E. coli BL21 using pET 50b (+). Optimal recombinant protease expression was observed at 1 mM IPTG, 37 °C for 4 h. The resulting protease was observed in soluble form. The molecular mass estimated by SDS-PAGE and Western blot analysis of the protease (NprB) fused with His and Nus tag is ~70 KDa. The protease protein was purified by Ammonium sulfate precipitation and immobilized metal ion affinity chromatography. The optimum pH and temperature for protease activity using casein as substrate were 7.2 and 70 °C, respectively. The mature protease was active and retained 80% of its activity in a broad spectrum of pH 6-8 after 4 h of incubation. Also, the half-life of the protease at 70 °C was 4 h. EDTA (5 mM) completely inhibited the enzyme, proving the isolated protease was a metalloprotease. NprB activity was enhanced in the presence of Zn²⁺, Mn²⁺, Fe²⁺ and Ca²⁺, while Hg²⁺ and Ni²⁺ decreased its activity. Exposure to organic solvents did not affect the protease activity. The recombinant protease was stable in the presence of 10% organic solvents and surfactants. Further characterization showed that zinc-metalloprotease is promising for the detergent, laundry, leather, and pharmaceutical industries.