Membrane combined with hydrophilic macromolecules enhances protein refolding at high concentration

Membrane technology is important to the development of modern biotechnology. It has the potential to efficiently refold protein at high concentration that is still a challenge for pharmaceutical protein produced from inclusion bodies. This paper dealt with the application of a polysulfone hollow fiber membrane to protein refolding using recombinant human granulocyte colony-stimulating factor (rhG-CSF) as a model protein. Compared with dilution refolding at protein concentration of 1.0 mg/mL, the crossflow membrane system led to a 16% increase in soluble protein recovery, and a 3.3-fold increase in specific bioactivity. Addition of PEG 6 K at 2 g/L could further improve the soluble protein recovery up to 57%, the specific bioactivity up to 2.2 × 108 IU/mL. Addition of dextran at 5 g/L could increase the soluble protein recovery up to 63.6%, the specific bioactivity up to 2.30 × 108 IU/mL. By gently and gradually removing denaturant, ultrafiltration membrane system was demonstrated to be very helpful for protein refolding at high concentration. Combining with hydrophilic macromolecular of PEG or dextran could further increase its efficiency. PEG was able to promote the refolding intermediate of rhG-CSF to transfer into the native structure; whereas dextran could enhance protein refolding mainly by weakening shear stress-induced protein aggregation.