Elucidating the mitochondrial proteome of Toxoplasma gondii reveals the presence of a divergent cytochrome c oxidase

Abstract

The mitochondrion of apicomplexan parasites is critical for parasite survival, although the full complement of proteins that localize to this organelle has not been defined. Here we undertake two independent approaches to elucidate the mitochondrial proteome of the apicomplexan Toxoplasma gondii. We identify approximately 400 mitochondrial proteins, many of which lack homologs in the animals that these parasites infect, and most of which are important for parasite growth. We demonstrate that one such protein, termed TgApiCox25, is an important component of the parasite cytochrome c oxidase (COX) complex. We identify numerous other apicomplexan-specific components of COX, and conclude that apicomplexan COX, and apicomplexan mitochondria more generally, differ substantially in their protein composition from the hosts they infect. Our study highlights the diversity that exists in mitochondrial proteomes across the eukaryotic domain of life, and provides a foundation for defining unique aspects of mitochondrial biology in an important phylum of parasites.

Identification of the Toxoplasma gondii mitochondrial ribosome, and characterisation of a protein essential for mitochondrial translation

“…B). The signal obtained by complex IV activity assay corresponds to the size reported for T. gondii complex IV recently (Seidi et al , ) supporting the assay's specificity. To further confirm its identity as complex IV, we performed mass spectrometry analysis of this band which confirmed the complex identity, through confirming the presence of all complex IV components (Table ).…”

“…Mitochondrial targeting predictions were done using MitoProt II (https://ihg.gsf.de/ihg/mitoprot.html) and Predotar (https://urgi.versailles.inra.fr/predotar/). The presence (Yes) or absence (No) of the gene product in the proximity tagging‐based mitochondrial proteome is shown (Seidi et al , ) (No – no mass spectrometry data; No* – mass spectrometry data found but the gene is not included in the final list of 421 genes). The fitness score is based on the whole genome CRISPR/CAS9 screen (Sidik et al , ).…”

“…While methods that may resolve this complication are being explored (Hata et al , ), other strategies that bypass the reliance on organelle isolation are being utilised. Recent biotin‐proximity tagging approaches have made a big step forward by identifying a large proportion of the mitochondrial matrix proteins (Seidi et al , ). The number of 421 proposed mitochondrial proteins identified is predicted to be markedly smaller than the total number of mitochondrial proteins estimated through comparison to other species (Panigrahi et al , ; Salvato et al , ; Smith and Robinson, ).…”

“…), 4 were predicted to be ribosomal subunits (Table ), we localised 2 other predicted mitoribosomal proteins (Fig. and Table ) and validation of mitochondrial localisation was provided for 4 more components in the proximity tagging study (Seidi et al , ). Table summarises the localisation information available for predicted mitoribosomal proteins in T. gondii as well as provide new notations in agreement with the fields' standard (Greber and Ban, ).…”

“…These data expand the group of validated mitochondrial proteins by 11%. Only 4 of these 10 are predicted in the Seidi et al (2018) dataset of 421 genes (Table S3), and either 2 or 3 of them are not predicted to target the mitochondrion in two different algorithms (Table S3). In doing so, our search strategy makes a contribution to the ongoing efforts in the field.…”