Characterization of plasmepsin IV, an aspartic protease of malaria parasite Plasmodium vivax

초록

A family of aspartic proteases called plasmepsins of Plasmodium species is known to participate in a wide variety of cellular processes essential for parasite survival. Therefore, plasmepsins of malaria parasites have recognized as attractive antimalarial drug targets. Although plasmepsins of P. falciparum have been extensively characterized, only a little information is currently available for plasmepsins of P. vivax. To expand our understanding of plasmepsins of P. vivax, we expressed P. vivax plasmepsin IV (PvPM4) in Escherichia coli and characterized the biochemical properties of the recombinant protein. The autocatalytic processing of PvPM4 was induced at acidic pH, but not neutral and alkali conditions. The optimal pH for PvPM4 was pH 4.5 and the enzyme was relatively stable in acidic and neutral conditions. To better characterize the determinants of folding for PvPM4, multiple constructs with or without different length of prodomain of the enzyme were expressed in E. coli and assessed their abilities to refold. The minimum length of prodomain required for folding of PvPM4 was determined to be C-terminal 41 amino acid residues of the prodomain. PvPM4 readily hydrolyzed native human hemoglobin at acidic conditions and partially hydrolyzed erythrocyte membrane proteins such as spectrin and band 3 at neutral pH. These results suggested that PvPM4 is an active hemoglobinase of P. vivax and is also potentially involved in disruption of the erythrocyte cytoskeleton to allow egress of parasite from erythrocyte.