Effect of TAT-signaling fusion system along with co-expression of GroEL/ES chaperones on secretory expression of somatropin

Human growth hormone (somatropin) is one of the most widely used recombinant proteins that stimulates growth, cell reproduction, and cell regulation in humans. Synthetic production of this protein normally results in low yields and inclusion body formation. To overcome these difficulties, the production of somatropin along with two common signal peptides, namely TorA and SufI, in co-expression with a cytosolic chaperone, GroEL/ES, was evaluated in the present study. The target protein and the two signal sequences (TorA and SufI) were synthesized and cloned into an expression plasmid (pET-22) by using Nde l and Xho l endonucleases. The expression vector (pGro7) containing chaperone proteins (GroES/EL) and one of the expression vectors containing the signal sequence (and the target protein) were co-expressed in the BL21 DE3 expression host. The results showed that although some of the expressed proteins exit the cytoplasm and enter the periplasmic space, there is also an accumulation of proteins (probably as inclusion body) inside the cytoplasmic area. Western blot analysis showed that the inclusion of a signal sequence in the cassette containing the target protein could help to secrete the protein in the periplasmic space and culture media when compared with control groups. The result of these experiments show that the TAT secretion system promotes transportation of the target protein out of the cytoplasm. This secretory system completes folding of the protein structure and transfers the mature protein to the periplasmic space.