Expression and purification of Plasmodium falciparum MSP-1(42): A malaria vaccine candidate.

The C-terminal 42.10(3) Da portion of the merozoite surface protein (MSP-1) of the human malaria parasite Plasmodium falciparum is of interest, not only because it may constitute an essential part of a future anti-malaria vaccine, but also due to its role during the infection of erythrocytes by the parasite. We have cloned and expressed two synthetic DNA sequences encoding the two prototypic MSP-1(42) variants in E. coli. When over-produced, both proteins form insoluble aggregates which were isolated in high purity and yield. After solubilisation and refolding in vitro, both proteins were purified to homogeneity by a three-step procedure applying Ni-chelate, size exclusion and immuno-affinity chromatography. After purification, both proteins meet key criteria of preparations for clinical use. First, conformational studies suggest proper folding of the proteins, particularly in the region containing two EGF-like domains. Polyclonal serum raised against E. coli produced MSP-1(42) recognizes native MSP-1 in Plasmodium infected erythrocytes as shown by immunofluorescence.