Purification and refolding of Escherichia coli-expressed recombinant human interleukin-2

The expression of rhIL-2 (recombinant human interleukin-2) in bacteria results in the formation of insoluble inclusion-body aggregates. These aggregates were first solubilized under denaturing conditions (sodium phosphate buffer solution containing 8 M urea and 10 mM 2-mercaptoethanol) and then purified using IMAC (immobilized metal-ion-affinity chromatography). IMAC was used to capture rhIL-2. The protein was gradually refolded on the column by a gradient elution (8 M to 0 M urea) in the presence of 10% (v/v) glycerol. Glycerol was used to prevent protein aggregation during the refolding step. Using this method, rhIL-2 was collected at 97% purity and its activity was measured by the lymphocyte transformation test. The measured activity was identical with commercial human interleukin-2.