Cloning, expression and purification of extracellular serine protease Esp, a biofilm-degrading enzyme, from Staphylococcus epidermidis

Aims: Staphylococcus epidermidis Esp, an extracellular serine protease, inhibits Staphylococcus aureus biofilm formation and nasal colonization. To further expand the biotechnological applications of Esp, we developed a highly efficient and economic method for the purification of recombinant Esp based on a Brevibacillus choshinensis expressionsecretion system. Methods and Results: The esp gene was fused with the N-terminal Sec-dependent signal sequence of the B. choshinensis cell wall protein and a C-terminal hexa-histidine-tag gene. The recombinant Esp was expressed and secreted into the optimized medium as an immature form and subsequently activated by thermolysin. The mature Esp was easily purified by a single purification step using nickel affinity chromatography and showed proteolytic activity as well as Staph. aureus biofilm destruction activity. Conclusions: The purification yield of the developed extracellular production system was 5 mg recombinant mature Esp per 20-ml culture, which was much higher than that of an intracellular production system in Escherichia coli (3 mg recombinant Esp per 1-l culture). Significance and Impact of the Study: Our findings will be a powerful tool for the production and purification of recombinant Esp and also applicable to a large variety of recombinant proteins used for basic researches and biotechnological applications.