Improving the mda-7/IL-24 refolding and purification process using optimized culture conditions based on the structure characteristics of inclusion bodies

Abstract

Background: The melanoma differentiation-associated gene-7 (mda-7)/interleukin-24 (IL-24) can induce apoptosis in a wide variety of tumor cell types, whereas it has no toxicity in normal cells. However, recombinant human mda-7/IL-24 is difficult to obtain from Escherichia coli because of its insolubility. Results: In this study, we improved the structure of inclusion bodies (IBs) by optimizing the induction temperature, pH, concentrations of inducer, and metal ion additives. Statistically designed experimental analyses of three metal ion factors were performed using the Box-Behnken design. Induction temperature of 30°C, pH 7.0, and 0.1 mM isopropyl-β-D-thiogalactopyranoside (IPTG) were selected, and the optimized levels for the factors predicted by the model comprised the following: Mg2+ (15.7 mM), Ca2+ (16.6 mM), and Mn2+ (3.0 mM). The optimized culture conditions improved the structure of the IBs, which was validated by scanning electron microscopy (SEM) and the increase of IBs solubility. Conclusions: After optimization, IB solubility and renatured mda-7/IL-24 increased by 51% and 84%, respectively. This study also provided a simple purification method of specific IB washing steps. Manipulating the fermentation parameters to optimize the refolding and purification process is likely to be widely applicable to other proteins.