Improving protein solubility using short Solubility Enhancement Peptide (SEP) tags

High level of stability and solubility are required for the industrial application of proteins and enzymes. We developed a highly versatile technique for improving a protein’s solubility without changing the buffer condition, which in turn increases expression and purification yields. Our protein solubilization technique is simple and consists of attaching a short solubility enhancement peptide sequence (SEP-tag; 7-10 residues) to the N or C terminus of the protein. We used the SEP tag to increase the solubility of our model protein, Bovine Pancreatic Trypsin Inhibitor, by 400% (Fig.1), which enabled to prepare highly concentrated Nuclear Magnetic Resonance samples, reducing the measurement time to 1/8. Furthermore, SEP-tags significantly reduce the formation of inclusion body formation in E coli (Fig.2). The advantages of SEP tags compared to previously developed techniques are: 1) The tag’s molecular mass is small, so the influence on the target protein’s function is minimal; 2) Because the SEP tags function in a unfolded state, it can be used under a wide range of temperatures, pH values and salt concentrations. The potential scope for application of this technique is wide, and we are seeking to apply it to fields such as proteomics or the production of therapeutic proteins.