Periplasmic expression and recovery of human interferon gamma in Escherichia coli

A synthetic human interferon gamma (hIFN-γ) gene was fused to SP1 and SP3, two Sec-dependent artificial signal peptides to transport the hIFN-γ to the periplasm of Escherichia coli BL21-SI. The processing efficiency of both SP1-hIFN-γ and SP3-hIFN-γ was dependent on the culture medium as well as the post-induction temperature. Both precursors were processed completely when cells were cultured using minimal medium and a post-induction temperature of 32.5 °C, and only the processed hIFN-γ was detected. The SP3 signal peptide was more efficient than SP1 for the secretion of hIFN-γ. Sixty percent of the total hIFN-γ was secreted to the periplasm using the SP3 signal peptide and a post-induction temperature of 20 °C. Using Tris-sucrose-dithiothreitol (TSD) hypertonic buffer, the periplasmic soluble hINF-γ was recovered with a purity of 85%.