A key cytosolic iron–sulfur cluster synthesis protein localizes to the mitochondrion of Toxoplasma gondii

• Published in: Molecular microbiology Vol. 115; no. 5; pp. 968 - 985
• Main Authors: Aw, Yi Tong Vincent, Seidi, Azadeh, Hayward, Jenni A., Lee, Jiwon, Makota, F. Victor, Rug, Melanie, Dooren, Giel G.
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.05.2021
• Subjects: Apicomplexa; Biosynthesis; Chemical synthesis; Clusters; Electron transfer; Eukaryotes; Homology; Iron; iron–sulfur cluster; Localization; Malaria; Membranes; Mitochondria; Parasites; Prostheses; Prosthetic groups; Protein biosynthesis; Proteins; Sulfur; Toxoplasma; Toxoplasma gondii; Toxoplasmosis; Vector-borne diseases; Toxoplasma; Apicomplexa; iron-sulfur cluster; mitochondria
• DOI: 10.1111/mmi.14651
• ISSN: 0950-382X

Iron–sulfur (Fe‐S) clusters are prosthetic groups on proteins that function in a range of enzymatic and electron transfer reactions. Fe‐S cluster synthesis is essential for the survival of all eukaryotes. Independent Fe‐S cluster biosynthesis pathways occur in the mitochondrion, plastid, and cytosolic compartments of eukaryotic cells. Little is known about the cytosolic Fe‐S cluster biosynthesis in apicomplexan parasites, the causative agents of diseases such as malaria and toxoplasmosis. NBP35 serves as a key scaffold protein on which cytosolic Fe‐S clusters assemble, and has a cytosolic localization in most eukaryotes studied thus far. Unexpectedly, we found that the NBP35 homolog of the apicomplexan Toxoplasma gondii (TgNBP35) localizes to the outer mitochondrial membrane, with mitochondrial targeting mediated by an N‐terminal transmembrane domain. We demonstrate that TgNBP35 is critical for parasite proliferation, but that, despite its mitochondrial localization, it is not required for Fe‐S cluster synthesis in the mitochondrion. Instead, we establish that TgNBP35 is important for the biogenesis of cytosolic Fe‐S proteins. Our data are consistent with TgNBP35 playing a central and specific role in cytosolic Fe‐S cluster biosynthesis, and imply that the assembly of cytosolic Fe‐S clusters occurs on the cytosolic face of the outer mitochondrial membrane in these parasites. Iron‐sulfur clusters have functioned as important prosthetic groups on proteins since life first evolved. Iron‐sulfur clusters that are synthesized in the cytosol of eukaryotes are assembled on a molecular scaffold that includes the protein NBP35. Here, we show that the NBP35 homolog from the apicomplexan parasite Toxoplasma is critical for parasite proliferation, but, surprisingly, that it localizes to the mitochondrion. Despite this mitochondrial localisation, we demonstrate that Toxoplasma NBP35 contributes to cytosolic iron‐sulfur cluster synthesis.