Abstract
BACKGROUND: The protein hormone granulocyte colony-stimulating factor (GCSF) stimulates the production of white blood cells and plays an important role in medical treatment of cancer patients. METHODS: An efficient process was developed for heterologous expression of the human GCSF in E. coli BL21 (DE3). The feeding rate was adjusted to achieve the maximum attainable specific growth rate under critical value. In this method, specific growth rate was maintained at the maximum value of 0.55 h⁻¹ at the beginning of feeding to 0.4 h-1 at the induction time. Recombinant human GCSF (rh-GCSF) was produced as inclusion body. At first, inclusion bodies were released by cell disruption and then washed, solubilized and refolded. Finally, the rh-GCSF was purified by cation exchange chromatography. RESULTS: Obviouly, higher specific growth rate decreases process time and consequently increases productivity. The final concentration of biomass and GCSF was achieved 126 g DCW.l⁻¹ and 32.1 g.l⁻¹. Also, the final specific yield (YP/X) and total productivity of rh-GCSF were obtained 254 mg.g⁻¹ DCW and 1.83 g.l⁻¹.h⁻¹, respectively. According to the available data, this is one of the highest YP/X and productivity that has been reported for any human protein which is expressed in E. coli. Recovery yield of purification process was %40 and purity of recombinant protein was over than 99%. The circular dichroism spectra of purified rh-GCSF, Neupogen and PD-Grastim showed that all proteins have a similar secondary structure. CONCLUSION: Modified exponential feeding strategy for fed-batch cultivation of recombinant E. coli, results in minimum fed-batch duration and maximum productivity.