Development of high-performance inducible and secretory expression vector and host system for enhanced recombinant protein production

The production of lipopolysaccharide (LPS)-free recombinant proteins from culture supernatants is of great interest to biomedical research and industry. Due to the LPS-free cell wall structure and the well-defined secretion factor B (SecB)-dependent secretion pathway, Gram-positive bacteria are a superior alternative to Escherichia coli expression systems. However, the lack of inducible expression systems for high yields has been a bottleneck. To address this, we developed the pKS81 plasmid, featuring the uhpT (glucose-6-phosphate [G6P] transporter) promoter for high expression of recombinant proteins induced by extracellular G6P via a three-component hexose phosphate transport regulatory system (HptARS), the N-terminal SecB-dependent signal peptide sequence for recombinant protein secretion, and the C-terminal 8 × histidine tag for purification by nickel affinity chromatography. We also generated an expression host strain, Staphylococcus aureus LAC9, lacks the uhpT gene and harmful superantigen and leukotoxin genes, allowing for constitutive HptARS activation by extracellular G6P and increased safety, respectively. Using the pKS81 plasmid, we successfully achieved high yields of prokaryotic (staphylococcal leukotoxin E) and eukaryotic (human annexin A2 protein tagged with mouse IgG1) recombinant proteins, up to 900 mg/L. Our newly established inducible and secretory expression system provides for efficient production and easy purification of LPS-free recombinant proteins, making it valuable for biomedical research and industrial applications.