The Small Metal-Binding Protein SmbP Improves the Expression and Purification of the Recombinant Antitumor-Analgesic Peptide from the Chinese Scorpion Buthus martensii Karsch in Escherichia coli

We have recently shown that SmbP, the small metal-binding protein of Nitrosomonas europaea, can be employed as a fusion protein to express and purify recombinant proteins and peptides in Escherichia coli. SmbP increases solubility, allows simple, one-step purification through affinity chromatography, and provides superior final yields due to its low molecular weight. In this work, we report for the first time the use of SmbP to produce a recombinant peptide with anticancer activity: the antitumor-analgesic peptide (BmK-AGAP), a neurotoxin isolated from the venom of the Chinese scorpion Buthus martensii Karsch. This peptide was expressed in Escherichia coli SHuffle for correct, cytoplasmic, disulfide bond formation and tagged with SmbP at the N-terminus to improve its solubility and allow purification using immobilized metal affinity chromatography. SmbP_BmK-AGAP was found in the soluble fraction of the cell lysate. After purification and removal of SmbP by digestion with enterokinase, 1.8 mg of pure and highly active rBmK-AGAP was obtained per liter of cell culture. rBmK-AGAP exhibited antiproliferative activity on the MCF-7 cancer cell line, with a half-maximal inhibitory concentration value of 7.24 mu M. Based on these results, we considered SmbP to be a suitable carrier protein for the production of recombinant, biologically active BmK-AGAP. We propose that SmbP should be an attractive fusion protein for the expression and purification of additional recombinant proteins or peptides that display anticancer activities.