Overproduction of human granulocyte-colony stimulating factor fused to the PelB signal peptide in Escherichia coli

In an attempt to induce the secretion of human granulocyte-colony stimulating factor (hG-CSF) in Escherichia coli, the gene encoding mature hG-CSF was fused to the gene for the pectate lyase B (pelB) signal peptide of Erwinia caratovora, and fed-batch fermentation of the recombinant E. coli was performed. No secretion of hG-CSF and no processing of the signal peptide from the fusion protein was observed. Instead, the fusion protein, peIB-hG-CSF, at a concentration of ca. 1.7 g/l was produced in an inclusion body form. Interestingly, the biological activity of the purified fusion protein was found to be identical to that of mature hG-CSF, indicating that the pelB signal peptide attached to the N-terminal of hG-CSF had no effect on its biological activity.