Expression of soluble human interleukin-2 receptor alpha-chain in Escherichia coli

A soluble, biologically active form of IL-2R alpha known as delta MST and consisting of the 178 N-terminal amino acid residues of the mature protein was directly expressed in the cytoplasm and the periplasm of Escherichia coli. Because it was not glycosylated, the E. coli protein was substantially less heterogeneous than delta MST expressed in insect cells. Nevertheless, it manifested equivalent biological activity in an IL-2 binding assay. The level of active delta MST production was higher when the protein was expressed in secretable form with a bacterial signal peptide than when it was produced in the cytoplasm, probably because the oxidizing environment and the presence of disulfide isomerases in the periplasm facilitated the correct folding of delta MST.