Biosynthesis of heme O in intraerythrocytic stages of Plasmodium falciparum and potential inhibitors of this pathway.

A number of antimalarial drugs interfere with the electron transport chain and heme-related reactions; however, the biosynthesis of heme derivatives in Plasmodium parasites has not been fully elucidated. Here, we characterized the steps that lead to the farnesylation of heme. After the identification of a gene encoding heme O synthase, we identified heme O synthesis in blood stage parasites through the incorporation of radioactive precursors. The presence of heme O synthesis in intraerythrocytic stages of Plasmodium falciparum was confirmed by mass spectrometry. Inabenfide and uniconazole-P appeared to interfere in heme synthesis, accordingly, parasite growth was also affected by the addition of these drugs. We conclude that heme O synthesis occurs in blood stage-P. falciparum and this pathway could be a potential target for antimalarial drugs.

Heme A synthesis and CcO activity are essential for Trypanosoma cruzi infectivity and replication.

Trypanosoma cruzi, the causative agent of Chagas disease, presents a complex life cycle and adapts its metabolism to nutrients' availability. Although T. cruzi is an aerobic organism, it does not produce heme. This cofactor is acquired from the host and is distributed and inserted into different heme-proteins such as respiratory complexes in the parasite's mitochondrion. It has been proposed that T. cruzi's energy metabolism relies on a branched respiratory chain with a cytochrome c oxidase-type aa3 (CcO) as the main terminal oxidase. Heme A, the cofactor for all eukaryotic CcO, is synthesized via two sequential enzymatic reactions catalyzed by heme O synthase (HOS) and heme A synthase (HAS). Previously, TcCox10 and TcCox15 (Trypanosoma cruzi Cox10 and Cox15 proteins) were identified in T. cruzi They presented HOS and HAS activity, respectively, when they were expressed in yeast. Here, we present the first characterization of TcCox15 in T. cruzi, confirming its role as HAS. It was differentially detected in the different T. cruzi stages, being more abundant in the replicative forms. This regulation could reflect the necessity of more heme A synthesis, and therefore more CcO activity at the replicative stages. Overexpression of a non-functional mutant caused a reduction in heme A content. Moreover, our results clearly showed that this hindrance in the heme A synthesis provoked a reduction on CcO activity and, in consequence, an impairment on T. cruzi survival, proliferation and infectivity. This evidence supports that T. cruzi depends on the respiratory chain activity along its life cycle, being CcO an essential terminal oxidase.