Potential E. coli Expression Strategies for Production of Soluble Recombinant Streptokinases

The expression of recombinant protein for industrial and therapeutic applications, requires high yielding expression system like E. coli , which is easier to handle and satisfactory for various purposes. On other hand, one of the limitations of this system is Inclusion bodies formation. In this study, we optimized the conditions for the expression of the soluble form for three recombinant streptokinases (FSK, KSK, and FKSK). The change in culture conditions, like optical density, post-induction temperature, inducer concentration, media, and expression host had different effects on the expression levels of hybrid streptokinase proteins. The high amount of soluble fraction for FSK protein was in LB medium at 20°C in BL21 (DE3) and GJ1158. The amount of soluble protein was approximately 50%, but the amount of total protein at 20°C was lower than other induction temperatures. The high amount of soluble protein, expressed hybrid streptokinase (KSK) in LB medium at 30°C in BL21 (DE3) hosts, 0.5 O.D. cell densities were induced in 0.5mM IPTG. Approximately 70% of protein is soluble in these conditions. FKSK was never produced as a soluble form irrespective of any change in condition. All expressed FKSK protein appeared as inclusion bodies.