High efficient prokaryotic expression and purification of bioactive human growth hormone using a cleavable self-aggregating tag

Human growth hormone (hGH) is synthesized by the anterior pituitary gland and promotes cell proliferation and growth. This protein has been authorized to use for the treatment of various human growth disorders and until recently, substantial efforts have been made to upgrade the previous introduced strategies. Due to the small size of hGH and absence of posttranslational modifications, Escherichia coli is the ideal host for hGH production. In the present work, we employed a previously established cleavable self-aggregating tag (cSAT) for the expression and purification of hGH in BL21 (DE3) strain of E. coli to evaluate its effectiveness. The tag is composed of a self-cleavable intein and a self-assembling peptide ELK16 (Mxe GyrA intein-ELK16). At the first step, an active insoluble aggregate of the recombinant hGH-Mxe GyrA intein-ELK16 fusion protein was expressed through an efficient T7 based expression system and then purified with a simple centrifugation. The thiol reagent dithiothreitol (DTT) was then added to induce the intein-mediated cleavage and as a result the peptide released into the soluble fraction. Afterward, the hGH production was determined by SDS-PAGE and then the final concentration of released hGH was measured by the Bradford assay (4.96 mg/ml). Furthermore, the bioactivity of purified hGHs was confirmed by calculating its growth-stimulating effect using Nb2 cell line proliferation assay. All in all, the current study offers a straightforward and fast procedure for the production of pure and bioactive hGH in E. coli.