High-level expression of human insulin-like growth factor II in Escherichia coli

A gene encoding mature human insulin-like growth factor II (IGF-II) was constructed from the modified IGF-II cDNA sequence and two double-stranded synthetic oligodeoxynucleotide linkers. It was fused to a truncated lacZ gene such that IGF-II was expressed as part of C-terminus of beta-galactosidase. This fused lacZ'-IGF-II gene was under the control of tac promoter and we overproduced the beta-galactosidase-IGF-II fusion protein in the Escherichia coli. The fusion protein formed inclusion bodies inside the cells. The fusion protein was purified from the isolated inclusion bodies and IGF-II protein was obtained from their fusion protein by CNBr cleavage. The released IGF-II was confirmed by its molecular weight as determined by SDS-PAGE and by its ability to bind anti-IGF antibody.