Soluble expression of a functionally active Plasmodium falciparum falcipain-2 fused to maltose-binding protein in Escherichia coli.

Falcipain-2 (fp2) is a hemoglobinase required for supplying peptides and amino acids for the proliferation of Plasmodium falciparum in blood. The prospect of circumventing its activity thereby serves as a potential strategy for mining drugs for anti-malarial therapy. However, to date, efforts to express soluble and active fp2 in Escherichia coli have been futile. To overcome this problem, fp2 was expressed under an array of conditions including the exploitation of multiple gene constructs in eukaryotic and prokaryotic hosts. A series of experiments led to the finding that the placement of maltose-binding protein (MBP) before the fp2 mature domain was best in availing the soluble expression of the protease. The results also indicate that the prodomain impaired the bacterial expression of the protease and the amino acid residues at the N-terminal segment of mature fp2 can have a significant effect on the folding and solubility of the enzyme. The overexpressed MBP-fp2 fusion protein was purified and shown to be functionally active, providing a very useful alternative to the use of resolubilized enzyme for future study of structure and function of fp2.