Effects of ionic strength on inclusion body refolding at high concentration.

For commercial applications refolding process must be fast, inexpensive and highly efficient. In the past many strategies for protein refolding were introduced. Still, simple refolding methods with high product concentrations are still rare. Refolding experiments were performed with fructosyltransferase (FTF, EC 2.4.1.162) from Bacillus subtilis NCIMB 11871 produced as inclusion bodies. Solubilizates were refolded with batch dialysis or by continuous exchange of dialysis buffers with variable ionic strength. By employing dialysis with gentle removal of denaturant the dependence of protein concentration and decreasing refolding yields could be overcome compared to batch dialysis and yields were enhanced by 52% at protein concentrations of approx. 10 mg/mL. The average specific activity of refolded FTF was 123 U/mg, 83% relative to standard FTF. Rising ionic strength of refolding buffers to 600 mM leads to complete renaturation of solubilized protein at equal protein concentration. Buffer composition plays a less significant role on renaturation output. The effect might be correlated with ion charge density of co-solvents.