FTIR Investigation of Secondary Structure of Reteplase Inclusion Bodies Produced in Escherichia coli in Terms of Urea Concentration

Recent studies suggest that reducing the induction temperature would improve the quality of some recombinant inclusion bodies (IB) by providing a native-like secondary structure and leading to an improvement in protein recovery. This study focused on optimizing the solubilization condition of Reteplase, a recombinant protein with 9 disulfide bonds. The influence of lowering induction temperature and urea concentration was investigated on the secondary structure of the recombinant protein through FTIR analysis. Induction temperature reduction decreased the percentage of helixes and loops from 49 to 8. In addition, FTIR spectroscopy corroborates the drastic impact of this parameter on Reteplase secondary structure. Even though lowering urea concentration tripled the solubility of IBs expressed at lower induction temperature, the final yield is still quite low to be considered as optimum. On the other hand, the percentage of beta strands and turns in secondary structure of dissolved proteins were proportional to urea concentration. Therefore, in case of Reteplase, protein expression at low temperature (25°C) was not efficient to improve the protein recovery yield. Future studies need to focus on using other methods of solubilizing IBs to improve protein recovery.