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Published on: November 26, 2014
Evolutionary conservation and in vitro reconstitution of microsporidian iron-sulfur cluster biosynthesis
Sven-A Freibert1, Alina V Goldberg2, Christian Hacker3,4
1Institut für Zytobiologie und Zytopathologie, Philipps-Universität, Robert-Koch-Strasse 6, Marburg 35032, Germany.
Abstract:
Microsporidians are obligate intracellular parasites that have minimized their genome content and sub-cellular structures by reductive evolution. Here, we demonstrate that cristae-deficient mitochondria (mitosomes) of Trachipleistophora hominis are the functional site of iron-sulfur cluster (ISC) assembly, which we suggest is the essential task of these organelles. Cell fractionation, fluorescence imaging and immunoelectron microscopy demonstrate that mitosomes contain a complete pathway for [2Fe-2S] cluster biosynthesis that we biochemically reconstituted using purified mitosomal ISC proteins. The T. hominis cytosolic iron-sulfur protein assembly (CIA) pathway includes the essential Cfd1-Nbp35 scaffold complex that assembles a [4Fe-4S] cluster as shown by spectroscopic methods in vitro. Phylogenetic analyses reveal that the ISC and CIA pathways are predominantly bacterial, but their cytosolic and nuclear target Fe/S proteins are mainly archaeal. This mixed evolutionary history of Fe/S-related proteins and pathways, and their strong conservation among highly reduced parasites, provides compelling evidence for the ancient chimeric ancestry of eukaryotes.
Insights
Mitosomes in Trachipleistophora hominis are essential for iron-sulfur cluster assembly, a vital function despite their reduced structure. This finding reveals insights into parasite biology and eukaryotic evolution.
Area of Science:
- Cell Biology
- Parasitology
- Evolutionary Biology
Background:
- Microsporidians are obligate intracellular parasites with highly reduced genomes and organelles.
- Mitosomes, a type of mitochondrion found in microsporidians, are known for their simplified structure.
Purpose of the Study:
- To investigate the function of mitosomes in Trachipleistophora hominis.
- To determine the role of mitosomes in iron-sulfur cluster (ISC) assembly within these parasites.
Main Methods:
- Cell fractionation and fluorescence imaging.
- Immunoelectron microscopy.
- Biochemical reconstitution of the ISC pathway using purified proteins and in vitro spectroscopic analysis of the Cfd1-Nbp35 complex.
Main Results:
- Mitosomes of T. hominis host a complete pathway for [2Fe-2S] cluster biosynthesis.
- The cytosolic iron-sulfur protein assembly (CIA) pathway in T. hominis includes the Cfd1-Nbp35 scaffold complex, which assembles a [4Fe-4S] cluster.
- Phylogenetic analysis indicates bacterial origins for ISC and CIA pathways, but archaeal origins for target Fe/S proteins.
Conclusions:
- Mitosomes are essential for ISC assembly in T. hominis.
- The mixed evolutionary origin of ISC and CIA pathways supports the chimeric ancestry of eukaryotes.
- Conserved ISC and CIA pathways in reduced parasites highlight their ancient importance.
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