Facile production of tag-free recombinant human interleukin-11 by transforming into soluble expression in Escherichia coli

Human interleukin-11 (IL-11) is considered as a difficult-to-express protein in prokaryotic expression systems because of its low expression level and high tendency to form inclusion bodies. The current source of recombinant human IL-11 (rhIL-11) for therapeutic use is mainly obtained from a fusion protein synthesized by Escherichia coli, which requires an additional operation to cleave the fusion tag. Herein, we reported a strategy for the direct expression of tag-free rhIL-11 in E. coli. To explore the soluble expression of rhIL-11 without fusion tags in E. coli, we inserted the rhIL-11 gene into a pBV220 plasmid which is characterized by employing a temperature-sensitive pR/pL promoter to manipulate the transcription and translation of the gene of interest. As a result, the tag free rhIL-11 was efficiently expressed in the soluble form in E. coli. A two-step chromatography method, Capto Butyl-S combined with Capto Q, was developed to efficiently purify the tag-free rhIL-11 from the supernatant of the cell lysate. The resultant rhIL-11 showed a compact and highly ordered structure, as validated by circular dichroism and intrinsic fluorescence emission spectra. Additionally, the biological activity of the purified rhIL-11 was evaluated by TF-1 cell proliferation experiments and the results demonstrated that the E. coli expressed rhIL-11 is biologically active.