Soluble Expression of Human Granulocyte Colony Stimulating Factor (hG-CSF) in Escherichia coli Expression System

Human granulocyte colony stimulating factor (hG-CSF) is a hematological growth factor that plays a crucial role in neutrophil production and differentiation. Some foreign biomolecules, especially of human origin, such as hG-CSF, sometimes aggregate because of different factors during expression and create inclusion bodies in Escherichia coli (E. coli). Refolding process is commonly used to recover these very valuable molecules, but still significant amounts of protein remain unusable. Refolding procedures are frequently costly, time-consuming, and not fully efficient. Therefore, the use of molecular chaperones to improve soluble expression of proteins was evaluated in the study. In this context, hG-CSF was co-expressed with five chaperone plasmid systems (pGro7, pG-KJE8, pG-Tf2, pKJE7, pTf16) to ensure the expression of hG-CSF in soluble form. Among these, the pKJE7 plasmid was found to be the most effective in obtaining hG-CSF in soluble form, yielding 92% purity after Ni-NTA affinity chromatography purification. The total yield of hG-CSF obtained was 1.6 mg per 1 L bacterial culture. The biological activity of the soluble hG-CSF was evaluated in human umbilical vein endothelial cells (HUVECs). A 24-hour interaction of hG-CSF with HUVECs resulted in a significant increase in cell viability at all applied doses, demonstrating its bioactivity. As a result, hG-CSF, which previously aggregated as an inclusion body in the E. coli expression system, was correctly folded by co-expression with chaperone proteins were obtained as more efficient and purer.