Single step intein-mediated purification of hGMCSF expressed in salt-inducible <Emphasis Type="Italic">E. coli</Emphasis>

Human granulocyte-macrophage colony stimulating factor (hGMCSF) is an important therapeutic cytokine. As a novel attempt to purify hGMCSF protein, without the enzymatic cleavage of the affinity tag, an intein-based system was used. The gene was fused by overlap extension PCR to the intein sequence at its N-terminal in pTYB11 vector. The hGMCSF was expressed as a fusion protein in E. coli BL21(DE3), and E. coli GJ1158. In the former, the protein was expressed as inclusion bodies and upon purification the yield was 7 mg/l with a specific activity of 0.5 × 10⁷ IU/mg. In salt-inducible E. coli GJ1158, hGMCSF was expressed in a soluble form at 20 mg/l and a specific activity of 0.9 × 10⁷ IU/mg. The intein-hGMCSF was purified on a chitin affinity column by cleaving intein with 50 mM DTT resulting in a highly pure 14.7 kDa hGMCSF.