Facile expression and purification of active human growth hormone in E. coli by a cleavable self-aggregating tag scheme

Human growth hormone (hGH) plays an important role in growth control, growth promotion, cell development, and regulation of numerous metabolic pathways in the human body and has been approved by the U.S. FDA for the treatment of several human dysfunctions. Over-expression of recombinant hGH (rhGH) affords a misfolded form in cytoplasm of Escherichia coli, and the refolding step required to obtain active rhGH greatly affects its production costs. Herein, the cleavable self-aggregating tag (cSAT) scheme was used for the expression and purification of rhGH in E. coli. Four aggregating tags (L6KD/α3-peptide/EFK8/ELK16) successfully drove rhGH into active protein aggregates. After the Mxe GyrA intein-mediated cleavage, 2.8–21.4 μg rhGH/mg wet cell weight was obtained at laboratory scale, of which the L6KD fusion achieved the highest rhGH yield. The further refined rhGH maintained 92% of the bioactivity compared to commercial rhGH. The self-assembling of the aggregating tag might physically separate the hGH polypeptide chains, which in turn was beneficial to its folding into the active form. This study provided a simple and cost-effective approach for active rhGH production, and suggested an opportunity for improve folding of recombinant proteins in E. coli.