A divergent mitochondrial 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 heme with hexacoordinate iron whose redox potential is tuned by axial His/Met ligands and surrounding residues to support electron transport chain (ETC) function. We have identified a previously 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 displays heterogeneous heme coordination despite conservation of His/Met ligands. We determined that Pfcyt c-2 has a redox potential of -278 ± 6 mV that is over 500 mV lower than canonical mitochondrial cyt c homologs (+250 mV) and contradicts a conserved ETC role. This anomalous redox potential is lower than any natural monoheme c-type cyt and reveals exceptional evolutionary tuning for a eukaryotic cyt c. Although Pfcyt c-2 displays signs of structural heterogeneity, it retains low-level peroxidase activity and global protein thermostability comparable to canonical cyt c proteins. These results reveal a new clade of eukaryotic cyt c proteins with divergent biochemical properties and biological roles, opening new scaffolds for mechanistic discovery and redox engineering of natural and abiological functions.