TheToxoplasma gondiimitochondrial transporter ABCB7 is essential for cytosolic iron-sulfur cluster biogenesis and protein translation

Abstract

Iron-sulfur (Fe-S) clusters are ubiquitous inorganic cofactors required for numerous essential cellular pathways. Since they cannot be scavenged from the environment, Fe-S clusters are synthesised de novo in cellular compartments such as the apicoplast, mitochondrion and cytosol. The cytosolic Fe-S cluster biosynthesis pathway relies on transport of an intermediate from the mitochondrial pathway. An ATP binding cassette (ABC) transporter called ABCB7 is responsible for this role in numerous commonly studied organisms, but its role in the medically important apicomplexan parasites has not yet been studied. Here we identify and characterise theToxoplasma gondiiABCB7 homolog. Genetic depletion shows that it is essential for parasite growth, and that disruption triggers partial stage conversion. Characterisation of the knock-down line highlights a defect in cytosolic Fe-S cluster biogenesis leading to defects in protein translation and other pathways including DNA and RNA replication and metabolism. Our work provides support for a broad conservation of the connection between mitochondrial and cytosolic in Fe-S cluster biosynthesis and reveal its importance for parasite survival.

HCF101 is a novel component of the CIA cytosolic iron-sulfur synthesis pathway in the human pathogenToxoplasma gondii

“…7). CTC proteins have so far not been functionally investigated in the parasite, but both TgABCB7 and TgNBP35 are essential for parasite growth and were both shown to be important for TgABCE1 stability [20,53]. Combining genome-wide data for potential essentiality and localization [46,54] to metal-binding site prediction algorithms [45], our previous assessment of the putative T. gondii cytosolic and nuclear Fe-S proteome highlighted proteins involved in key functions like genome reparation and maintenance, mRNA synthesis and protein expression [19].…”

“…Previous functional investigations of the CIA pathway in T. gondii focused on TgABCB7, a mitochondrial transporter presumably involved in providing a sulfur-containing precursor for further processing by the cytosolic Fe-S assembly machinery [53] and on TgNBP35, a Fe-S scaffolding protein of the CIA that displays an unusual association with the outer mitochondrial membrane in the parasites [20]. These two proteins are quite upstream in the CIA machinery, and imply that the assembly of cytosolic Fe-S clusters likely happens at the cytosolic face of the mitochondrion in T. gondii , and then probably shuttle through the T. gondii NAR1 homologue to the CTC for subsequent transfer to client proteins (Fig.…”