Optimization of human granulocyte macrophage-colony stimulating factor (hGM-CSF) expression using asparaginase and...

The toxicity of the recombinant protein towards the expression host remains a significant deterrent for bioprocess development. In this study, the expression of human granulocyte macrophage-colony stimulating factor (hGM-CSF), which is known to be toxic to its host, was enhanced many folds using a combination of genetic and bioprocess strategies in Escherichia coli. The N terminus attachment of endoxylanase and asparaginase signal sequences from Bacillus subtilis and E. coli, respectively, in combination with and without His-tag, considerably improved expression levels. Induction and media optimization studies in shake flask cultures resulted in a maximal hGM-CSF concentration of 365 mg/L in the form of inclusion bodies (IBs) with a specific product yield (Y (P/X)) of 120 mg/g dry cell weight in case of the asparaginase signal. Culturing the cells in nutrient rich Terrific broth maintained the specific product yields (Y (P/X)) while a 6.6-fold higher volumetric concentration of both product and biomass was obtained. The purification and refolding steps were optimized resulting in a 95% pure protein with a fairly high refolding yield of 45%. The biological activity of the refolded protein was confirmed by a cell proliferation assay on hGM-CSF dependent human erythroleukemia TF-1 cells. This study demonstrated that this indeed is a viable route for the efficient production of hGM-CSF.