Enhanced soluble expression and effective purification of recombinant human interleukin-11 by SUMO fusion in <em>Escherichia coli</em>

Abstract

Human interleukin-11 is a multifunctional cytokine applied for the clinical treatment of thrombocytopenia. However, IL-11 has been considered a difficult protein in to express in an <em>Escherichia coli</em> expression system. Here, we demonstrate a suitable construction for high production of recombinant human interleukin-11 (rhIL-11) in <em>E. coli</em>. An optimized codon gene encoding human IL-11 was inserted in-frame with the small ubiquitin like modifier (SUMO) protein in the pE-SUMO3 vector. The SUMO IL-11 fusion protein was entirely expressed in soluble form and reached 31.6% of total soluble protein in <em>E. coli</em>. The rhIL-11 protein with a purity of over 99% was obtained at high protein yields of 320 mg rhIL-11 per liter of bacterial culture. Bioactivity of rhIL-11, as determined by proliferation of a TF-1 cytokine-dependent cell line, was 4.17 x 10⁵ unit/mg, similar to the activity of the natural protein. Interestingly, the rhIL-11 was purified easily and effectively due to its selective precipitation from the reaction mixture. To the best of our knowledge, this is the first report demonstrating self-aggregating recombinant protein after cleavage from SUMO. Thus, expression of rhIL-11 fused with SUMO yielded greatly increased soluble production and convenient purification, and could offer a potential drug candidate for deployment in clinical trials.