Enhancement of stability of recombinant streptokinase by intracellular expression and single step purification by hydrophobic interaction chromatography

Maintenance of stability, high biological activity and purity are essential requirements for recombinant therapeutic products and processes must be designed to meet these needs. This work addresses issues related to obtaining a high amount of stable recombinant streptokinase in its soluble form and a method to purify it in a single step with high levels of recovery and purity. The streptokinase gene without its native signal peptide was cloned and expressed in Escherichia coli, using the pRSETB expression vector. A significant amount of the expressed streptokinase was found in the soluble form in the cytoplasm. With an inducer concentration of 0.1 mM IPTG, recombinant streptokinase accumulated to about 20% of the total soluble protein in the cell. The biomass-specific activity of recombinant streptokinase obtained in the intracellular expression system (∼20,000 IU/mg DCW) was two-fold higher than the maximum reported in the literature. Furthermore, the expressed soluble protein was found to be highly stable. A higher concentration of the recombinant protein obtained from the intracellular system enabled single-step purification by hydrophobic interaction chromatography, with nearly 100% purity and 68% recovery. The whole process of expression and purification involved a minimal set of operations and would be very useful for economic production on a large scale of proteins like streptokinase which have therapeutic significance.