Structural characterization of recombinant streptokinase following recovery from inclusion bodies using different chemical solubilization treatments

•Protein solubilization from E. coli inclusion bodies was done using various concentrations of chemicals.•After protein solubilization from inclusion bodies by various concentrations of chemicals, intensities of rSK CD signals were varied.•The obtained rSK contained different amounts of secondary structures and biological potency. Circular dichroism (CD) in far-UV region was employed to study the extent of changes occurred in the secondary structures of recombinant streptokinase (rSK), solubilized from inclusion bodies (IBs) by different chemicals and refolded/purified by chromatographic techniques. The secondary structure distribution of rSK, obtained following different chemical solubilization systems, was varied and values in the range of 12.4–14.5% α-helices, 40–51% β-sheets and 35.5–48.3% turns plus residual structures were found. With reducing the concentration of chemicals during IB solubilization, the content of turns plus random coils was diminished and simultaneously the amounts of α- and β-sheets were increased. These changes in the secondary structures would lower the hydrophobicity along with the chance of protein aggregation and expose the hydrophilic regions of the protein. Therefore, these alterations in the secondary structures, occurred following efficient IBs solubilization by low concentration of chemicals, could be related to enhancement in rSK biological potency previously observed.