Two-step chromatographic purification of recombinant Plasmodium falciparum circumsporozoite protein from Escherichia coli.

The Plasmodium falciparum circumsporozoite (PfCS) protein (aa 19-405) has been cloned and expressed in E. coli. The protein was purified in a two-step process that was rapid and reproducible. E. coli cells were grown to a high density before induction for 1 h. Cells were disrupted by high pressure microfluidization and the total bacterial protein solubilized in 6 M Gu-HCl. The protein was refolded while bound to Ni-NTA agarose by exchange of 6 M Gu-HCl for 8 M urea and then slow removal of the urea. The eluted protein was further purified on Q Sepharose Fast Flow using conditions developed to remove E. coli proteins and reduce endotoxin (to 10 EU/50 microg). Yield was 20 mg of PfCS protein from 10 g of wet cell paste. The final protein product bound to HepG2 liver cells in culture and inhibited the invasion of those cells by sporozoites in an ISI assay greater than 80% over control cultures when used at 10 microg/ml.