Loveridge, K. M. | bioRxiv Science

bioRxiv2025

A Divergent Cytochrome c in Malaria Parasites with an Anomalously Low Redox Potential

Eukaryotic cytochrome (cyt) c is a highly conserved mitochondrial protein central to cellular respiration, featuring a covalently attached hexacoordinate heme whose redox potential is tuned by axial His/Met ligands and surrounding residues to support electron transport chain (ETC) function. We have identified an unrecognized lineage of eukaryotic cyt c homologs in Apicomplexa, a phylum of intracellular pathogens that includes Plasmodium falciparum malaria parasites. P. falciparum cyt c-2 (Pfcyt c-2) exemplifies this divergent lineage and has an unusual pentacoordinate heme despite conservation of His/Met ligands. We determined that Pfcyt c-2 has a redox potential of -278 mV that is over 500 mV lower than canonical cyt c homologs (+250 mV) and contradicts a conserved ETC role. This anomalous redox potential is lower than any natural monoheme c-type cyt. Nevertheless, Pfcyt c-2 displays canonical thermostability and low-level peroxidase activity, while showing signs of elevated structural heterogeneity. These results reveal a new clade of eukaryotic cyt c variants with divergent biochemical properties and biological roles, opening new scaffolds for mechanistic discovery and redox engineering.

biochemistry↗

bioRxiv2024

Unraveling mechanisms of iron acquisition in malaria parasites

Plasmodium falciparum malaria parasites invade and multiply inside red blood cells (RBCs), the most iron-rich compartment in humans. Like all cells, P. falciparum requires nutritional iron to support essential metabolic pathways, but the critical mechanisms of iron acquisition and trafficking during RBC infection have remained obscure. Parasites internalize and liberate massive amounts of heme during large-scale digestion of RBC hemoglobin within an acidic food vacuole (FV) but lack a heme oxygenase to release porphyrin-bound iron. Although most FV heme is sequestered into inert hemozoin crystals, prior studies indicate that trace heme escapes biomineralization and is susceptible to non-enzymatic degradation within the oxidizing FV environment to release labile iron. Parasites retain a homolog of divalent metal transporter 1 (DMT1), a known mammalian iron transporter, but its role in P. falciparum iron acquisition has not been tested. Our phylogenetic studies indicate that P. falciparum DMT1 (PfDMT1) retains conserved molecular features critical for metal transport. We localized this protein to the FV membrane and defined its orientation in an export-competent topology. Conditional knockdown of PfDMT1 expression is lethal to parasites, which display broad cellular defects in iron-dependent functions, including impaired apicoplast biogenesis and mitochondrial polarization. Parasites are selectively rescued from partial PfDMT1 knockdown by supplementation with exogenous iron, but not other metals. These results support a cellular paradigm whereby PfDMT1 is the molecular gatekeeper to essential iron acquisition by blood-stage malaria parasites and suggest that therapeutic targeting of PfDMT1 may be a potent antimalarial strategy.

cell biology↗