In eukaryotes, heme attachment through two thioether bonds to mitochondrial cytochromes c and c1 is catalysed by either multi-subunit cytochrome c maturation system I or holocytochrome c synthetase (HCCS). The former was inherited from the α-proteobacterial progenitor of mitochondria; the latter is a eukaryotic innovation for which prokaryotic ancestry is not evident. HCCS provides one of few exemplars of de novo protein innovation in eukaryotes, but structure-function insight of HCCS is limited. Uniquely, euglenozoan protists, which include medically relevant kinetoplastids Trypanosoma and Leishmania parasites, attach heme to mitochondrial c-type cytochromes by a single thioether linkage. Yet the mechanism is unknown as genes encoding proteins with detectable similarity to any involved in cytochrome c maturation in other taxa are absent. Here, a bioinformatics search for proteins conserved in all hemoprotein-containing kinetoplastids identified kinetoplastid cytochrome c synthetase (KCCS), which we reveal as essential, mitochondrial, and catalyses heme attachment to trypanosome cytochrome c. KCCS has no sequence identity to other proteins, apart from slight resemblance within four short motifs suggesting relatedness to HCCS. Thus, KCCS provides a novel resource for studying eukaryotic cytochrome c maturation, possibly with wider relevance since mutations in human HCCS leads to disease. Moreover, many examples of mitochondrial biochemistry are different in euglenozoans as compared to many other eukaryotes; identification of KCCS thus, provides another exemplar of extreme, unusual mitochondrial biochemistry in an evolutionarily divergent group of protists.
|Publication status||Accepted/In press - 30 Mar 2021|