Expression of curcin–transferrin receptor binding peptide fusion protein and its anti-tumor activity

• A curcin–TfR binding peptide fusion protein was expressed in E. coli and purified.
• TfR binding peptide (TfRBP9) enhanced the ability of the curcin binding to HepG2.
• Compared with curcin, the curcin–TfRBP9 has higher cytotoxicity on HepG2.

Curcin can inhibit the proliferation of tumor cells and promote tumor cell apoptosis, but the cytotoxicity of curcin is not selective for tumors or normal cells. In order to enhance the targeting of the anti-tumor ability of curcin, a transferrin receptor (TfR) binding peptide, TfRBP9, was fused with curcin. The curcin–TfRBP9 gene was cloned into pQE-30 and the recombinant vector pQE-30–curcin–TfRBP9 was established. Then the recombinant vector pQE-30–curcin–TfRBP9 was transferred into Escherichia coli M15. After being induced by 0.5 mM IPTG for 6 h at 37 °C, the expressed quantity of the recombinant protein was about 30% of the total protein. Recombinant curcin–TfRBP9 was expressed in the form of an inclusion body. After dissolution, purification and renaturation, the purity of the recombinant curcin–TfRBP9 reached 95%. Immunofluorescence analysis showed that the TfRBP9 significantly enhanced the ability of the curcin binding to HepG2, and was enriched in the cytoplasm. The curcin–TfRBP9 fusion protein had significant proliferation inhibition effects on the HepG2 cells that over-expressed transferrin receptors, had lower inhibitory effects on the SKBR-3 cells that expressed low transferrin receptors, and had the lowest inhibitory effects on the LO-2 cells that were normal human liver cells. Compared with curcin, the curcin–TfRBP9 induced higher apoptosis rates in the HepG2 cells.