Biochemical properties and cellular localization of Plasmodium falciparum protein disulfide isomerase.

We have previously reported the isolation of a 52,000 M(r) protein (Pf52) displaying consensus sequences for thiol:disulfide oxidoreductases. Pf52 therefore represents the plasmodial protein disulfide isomerase (PDI). It has been renamed PfPDI and correlates to MAL8P1.17 in the annotated genome of P. falciparum (3D7 strain). Antibodies were raised against recombinant (His)(6)-tagged forms of PfPDI devoid of its signal peptide sequence, demonstrating a major co-localization of PfPDI with endoplasmic reticulum-resident proteins, PfBIP and PfERC, but not with the Golgi marker PfERD2. Recombinant PfPDI displayed typical biochemical functions of PDIs: oxidase/isomerase and reductase activities, as well as a chaperone-like behavior on the denaturated protein rhodanese. These activities were comparable to those measured for the purified native bovine PDI and the human recombinant PDI. The antiplasmodial compound DS61 does inhibit the recombinant PfPDI oxidase/isomerase activity but not that of the human recombinant PDI, suggesting structural differences between both enzymes. However, a discrepancy between the inhibitory activity of DS61 on the recombinant PfPDI (IC(50) of 430 microM) and its in vitro antiplasmodial activity (IC(50) of 0.1 microM) was observed, suggesting that PfPDI is not the only target of DS61. Taking into account its biochemical properties and its intracellular localization, the involvement of PfPDI in the parasite protein folding is discussed, as well as its potential for the development of alternative antimalarial chemotherapy strategies.