The ferredoxin‐NADP⁺ reductase/ferredoxin electron transfer system of Plasmodium falciparum

Abstract

In the apicoplast of apicomplexan parasites, plastidic-type ferredoxin and ferredoxin-NADP + reductase (FNR) form a short electron transport chain that provides reducing power for the synthesis of isoprenoid precursors. These proteins are attractive targets for the development of novel drugs against diseases such as malaria, toxoplasmosis, and coccidiosis. We have obtained ferredoxin and FNR of both Toxoplasma gondii and Plasmodium falciparum in recombinant form, and recently we solved the crystal structure of the P. falciparum reductase. Here we report on the functional properties of the latter enzyme, which differ markedly from those of homologous FNRs. In the physiological reaction, P. falciparum FNR displays a k cat five-fold lower than those usually determined for plastidic-type FNRs. By rapid kinetics, we found that hydride transfer between NADPH and proteinbound FAD is slower in the P. falciparum enzyme. The redox properties of the enzyme were determined, and showed that the FAD semiquinone species is highly destabilized. We propose that these two features, i.e. slow hydride transfer and unstable FAD semiquinone, are responsible for the poor catalytic efficiency of the P. falciparum enzyme. Another unprecedented feature of the malarial parasite FNR is its ability to yield, under oxidizing conditions, an inactive dimeric form stabilized by an intermolecular disulfide bond. Here we show that the monomer-dimer interconversion can be controlled by oxidizing and reducing agents that are possibly present within the apicoplast, such as H 2 O 2 , glutathione, and lipoate. This finding suggests that modulation of the quaternary structure of P. falciparum FNR might represent a regulatory mechanism, although this needs to be verified in vivo.

Compartmentation of Redox Metabolism in Malaria Parasites

“…This indicates that the phenomenon is a direct consequence of the translational process, supporting the leaky scanning model for ATI [37], [38]. In conclusion, the discovery of an antioxidative and redox-regulatory system within the apicoplast fills an important gap in our knowledge about this apicomplexan-specific organelle and has an impact on the interpretation of other studies [24], [42]. For example, the plastidic-type ferredoxin and ferredoxin-NADP + reductase (FNR) of P. falciparum provide electrons for the synthesis of isoprenoid precursors in the apicoplast [42].…”

“…In conclusion, the discovery of an antioxidative and redox-regulatory system within the apicoplast fills an important gap in our knowledge about this apicomplexan-specific organelle and has an impact on the interpretation of other studies [24], [42]. For example, the plastidic-type ferredoxin and ferredoxin-NADP + reductase (FNR) of P. falciparum provide electrons for the synthesis of isoprenoid precursors in the apicoplast [42]. FNR activity is controlled through monomer-dimer interconversion by oxidizing and reducing agents, such as H 2 O 2 and glutathione [42].…”

Reactions of Antimalarial Peroxides with Each of Leucomethylene Blue and Dihydroflavins: Flavin Reductase and the Cofactor Model Exemplified

“…[5] Given its functional relationship with Fre described here, it is also apparent that the flavoenzyme ferredoxin-NADP + reductase, which is present in the parasite apicoplast, [28] must also be susceptible. Such susceptibility may underpin the enhanced in vitro biological activities of artemisinins usually observed toward apicomplexan parasites, such as Plasmodium, Toxoplasma, and Babesia species as compared with activities toward non-apicomplexan parasites.…”

“…[23,25] In a malaria-infected erythrocyte, it is not known if the parasite uses flavin reductase for maintenance of redox homeostasis. A functionally related ferredoxin-NADP + reductase occurs in the parasite apicoplast, [28] and a chorismate synthase possessing flavin reductase activity has been detected in the parasite cytosol. [29] MB is a subversive substrate for each of parasite GR, TrxR, and lipoamide dehydrogenase in which the bound MB is reduced by the FADH 2 generated by reduction of Figure 1.…”

Thermococcus kodakarensis : the key to affordable biohydrogen production

“…In non-photosynthetic tissues and organisms, FNRs participate in the electron transfer chains of various other metabolic processes such as nitrogen fixation, sulfate assimilation, isoprenoid biosynthesis, osmotic and oxidative stress responses, and iron-sulfur cluster biogenesis [395][396][397][398][399][400][401][402]. However, in contrast to the FNRs involved in photosynthesis, the physiological direction of FNRs involved in these processes is toward the production of Fd red .…”