Getting ready for PAT: Scale up and inline monitoring of protein refolding of Npro fusion proteins

Screening for optimal refolding conditions for recombinant protein overexpressed in Escherichia coli as inclusion bodies is often carried out on micro-scale in non-agitated reactors. Currently, scale up of refolding of Npro fusion proteins is based on geometric similarity and constant Re number. Refolding/cleavage kinetics is recorded offline by HPLC and via fluorescence intensity. We show that the results for refolding obtained on the micro-scale can be transferred to the laboratory scale stirred tank reactor, with increases in scale up to a factor of 5000, with high agreement of kinetic constants and yield. Progress of refolding kinetics on the laboratory scale is monitored inline by attenuated total reflectance - Fourier transform infrared spectroscopy (ATR-FTIR). Addressing the demands for better process understanding, we demonstrate that ATR-FTIR enables the inline monitoring of refolding processes on the laboratory scale, replacing offline analysis which delivers the results with a time delay. Implementing inline monitoring will allow the integration of process control, thereby resulting in a more efficient and knowledge based production process.