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

Eukaryotic cytochrome (cyt) <i>c</i> 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 <i>c</i> homologs in Apicomplexa, a phylum of intracellular pathogens that includes <i>Plasmodium falciparum</i> malaria parasites. <i>P. falciparum</i> cyt <i>c</i>-2 (Pfcyt <i>c</i>-2) exemplifies this divergent lineage and has an unusual pentacoordinate heme despite conservation of His/Met ligands. We determined that Pfcyt <i>c</i>-2 has a redox potential of -278 mV that is over 500 mV lower than canonical cyt <i>c</i> homologs (+250 mV) and contradicts a conserved ETC role. This anomalous redox potential is lower than any natural monoheme <i>c</i>-type cyt. Nevertheless, Pfcyt <i>c</i>-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 <i>c</i> variants with divergent biochemical properties and biological roles, opening new scaffolds for mechanistic discovery and redox engineering.