[Recombination of human HER2 gene encoding the extracellular domain and purification of fusion protein]

To purify the extracellular domain of HER2 in vitro and improve its prokaryotic expression abundance, the cDNA fragment encoding extracellular domain of HER2 was obtained by PCR and cloned into the expression vector pGEX-6P-1. After transforming it into Escherichia coli BL21, we instituted an investigation of different inducing conditions to try out the optimal condition for expressing soluble fusion protein. As for insoluble inclusion bodies, they were dissolved in 8 M Urea and refolded in refolding buffer. The soluble protein and the refolded protein were purified with Glutathione Sepharose 4B, respectively. The results showed that both the soluble and insoluble protein existed in Escherichia coli, but the majority was insoluble. It is beneficial to the expression of soluble fusion protein by induction at lower temperature (30 degrees C) and higher optical density (A600= 1.8) with the use of certain additive in medium. By purification of the supernatant of the lysate and refolded protein, the yield of the fusion protein was about 1.23 mg per liter culture. As a result, we have obtained the maximum soluble extracellular domain of HER2 protein, and thus have laid a foundation for further work on functional study and antibody preparation for HER2.