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bioRxiv · 10.64898/2025.12.23.696199

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

Loveridge, K. M.·Olsen, O. D.·Scherer, S. R.·Espino-Sanchez, T. J.·Wienkers, H.·Hill, C. P.·Kay, M. S.·Sigala, P. A.
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Abstract

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.

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Loveridge, K. M., Olsen, O. D., Scherer, S. R., Espino-Sanchez, T. J., Wienkers, H., Hill, C. P., Kay, M. S., Sigala, P. A.. 2025-12-25. A Divergent Cytochrome c in Malaria Parasites with an Anomalously Low Redox Potential. https://doi.org/10.64898/2025.12.23.696199

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