On-column refolding and characterization of soluble human interleukin-15 receptor α-chain produced in Escherichia coli

Interleukin-15 receptor α-chain (IL-15Rα) is a member of the new cytokine receptor family, which possesses the sushi domain. To investigate the biochemical and biophysical characteristics of soluble human IL-15Rα (shIL-15Rα), shIL-15Rα was recombinantly expressed in Escherichia coli. The shIL-15Rα containing a six histidine-tag was expressed as inclusion bodies, which were solubilized with urea, immobilized on a Ni–nitrilotriacetic acid column, and refolded by a decreasing gradient of urea concentration. The refolded shIL-15Rα exhibited a highly flexible structure, neutralized human interleukin-15-induced cell proliferation effectively, and bound to its ligand with the same affinity as human IL-15Rα on the cell surface, as demonstrated by circular dichroism, a cell proliferation assay, and surface plasmon resonance, respectively. Thus, we succeeded in refolding shIL-15Rα to an active form on an affinity column.