Improved periplasmic production of biologically active murine interleukin-2 in Escherichia coli through a single amino acid change at the cleavage site

We fused the mature murine Interleukin-2 (mIL-2) gene to the signal peptide of the Outer membrane protein A (OmpA). We generated mutants mimicking different cleavage sites. A hybrid protein consisting of the OmpA signal peptide fused precisely to mature mIL-2, thereby mimicking the cleavage site of the OmpA native protein, was very poorly secreted into the periplasm of Escherichia coli (200 U/ml). Insertion of a serine residue between the OmpA signal peptide and the mIL-2 mature sequence, thus mimicking the mIL-2 natural cleavage site, increased the secretion by a factor of 40,000 (8 × l06 U/ml). The specific biological activity of secreted mIL-2 equaled that of natural mIL-2 and was about five times higher than that of mIL-2 refolded from inclusion bodies. We also show that the temperature at which the culture is grown has a major impact on the secretion level.