Plasmodium falciparummitochondrial complex III, the target of atovaquone, is essential for progression to the transmissible sexual stages

Abstract

ThePlasmodiummitochondrial electron transport chain (mETC) is responsible for essential metabolic pathways such asde novopyrimidine synthesis and ATP synthesis. The mETC complex III (cytochromebc1complex) is responsible for transferring electrons from ubiquinol to cytochromecand generating a proton gradient across the inner mitochondrial membrane, which is necessary for the function of ATP synthase. Recent studies revealed that the composition ofPlasmodiumcomplex III is divergent from humans, highlighting its suitability as a target for specific inhibition. Indeed, complex III is the target of the clinically used anti-malarial atovaquone and of several inhibitors undergoing pre-clinical trials, yet its role in parasite biology have not been thoroughly studied. We provide evidence that the universally conserved subunit, PfRieske, and the new parasite subunit, PfC3AP2, are part ofPlasmodium falciparumcomplex III (PfCIII), with the latter providing support for the prediction of its divergent composition. Using inducible depletion, we show that PfRieske, and therefore PfCIII as a whole, is essential for asexual blood stage parasite survival, in line with previous observations. We further found that PfCIII is essential for gametocyte maturation. These phenotypes are linked to defects in mitochondrial functions upon PfRieske depletion, including increased sensitivity to mETC inhibitors in asexual stages and decreased cristae abundance alongside abnormal mitochondrial morphology in gametocytes. This is the first study which explores the direct role of the PfCIII in gametogenesis via genetic disruption, paving the way for a better understanding of the role of mETC in the complex life cycle of these important parasites and providing further support for the focus of antimalarial drug development on this pathway.

Biogenesis of cytochromescandc1in the electron transport chain of malaria parasites

“…4E and Fig. S7 ), which is the expected size for Complex III dimer and consistent with recent BN-PAGE detections of Complex III in P. falciparum and Toxoplasma gondii (39–42). HCC 1 S knockdown in -aTc conditions, however, reduced the intensity of the 700 kDa band by ≥60%, suggesting a substantial defect in cyt c 1 assembly into Complex III.…”

“…1 ). Complex III is the molecular target of atovaquone (8) and has received considerable attention in the discovery and development of new antimalarial drugs (10, 12), especially as parasites that harbor atovaquone-resistant mutations are unable to complete mosquito-stage development and transmit to new hosts (44, 45). Prior work has also highlighted effective strategies to target parasites via Complex III during mosquito infection (11).…”

Identification of a divalent metal transporter required for cellular iron metabolism in malaria parasites

“…However, loss of ETC function and proton pumping sensitizes parasites to mitochondrial depolarization when the second mechanism is blocked by proguanil, such that positively charged dyes like MitoTracker fail to accumulate in mitochondria 56 . Prior knockdown studies of cytochrome c1 and Rieske in Complex III support this conclusion 12,48,60 .…”

“…However, when the mechanism is blocked by proguanil, dysfunction of the ETC sensitizes parasites to mitochondrial depolarization such that positively charged mitochondrial dyes like MitoTracker fail to accumulate in the organelle (58). Prior knockdown studies of cytochrome c 1 and Rieske in Complex III support this conclusion (13,49,62).…”