Abstract
Iron-sulfur proteins play an essential role in many biologic processes. Hence, understanding their assembly is an important goal. In Escherichia coli, the protein IscA is a product of the isc (iron-sulfur cluster) operon and functions in the iron-sulfur cluster assembly pathway in this organism. IscA is conserved in evolution, but its function in mammalian cells is not known. Here, we provide evidence for a role for a human homologue of IscA, named IscA1, in iron-sulfur protein biogenesis. We observe that small interfering RNA knockdown of IscA1 in HeLa cells leads to decreased activity of two mitochondrial iron-sulfur enzymes, succinate dehydrogenase and mitochondrial aconitase, as well as a cytosolic iron-sulfur enzyme, cytosolic aconitase. IscA1 is observed both in cytosolic and mitochondrial fractions. We find that IscA1 interacts with IOP1 (iron-only hydrogenase-like protein 1)/NARFL (nuclear prelamin A recognition factor-like), a cytosolic protein that plays a role in the cytosolic iron-sulfur protein assembly pathway. We therefore propose that human IscA1 plays an important role in both mitochondrial and cytosolic iron-sulfur cluster biogenesis, and a notable component of the latter is the interaction between IscA1 and IOP1.
Highlights
IscA1 is a homologue of the E. coli protein IscA [3], and at the mRNA level it is expressed in multiple tissues, including heart, kidney, cerebellum, and liver [21]
The importance of IscA in the bacterial iron-sulfur cluster assembly pathway and our previous work identifying a role for IOP1 in cytosolic iron-sulfur cluster assembly in mammalian cells lead us to investigate human IscA1 in more detail
The present results provide evidence that IscA1, the human homologue of the ancient protein IscA, plays a role in both mitochondrial and cytosolic iron-sulfur cluster assembly
Summary
FLAG-IOP1 (Fig. 2B), one possible explanation is that the contact site in IscA1 for IOP1 might not directly involve these cysteine residues, the cysteines, and potentially any associated iron-sulfur clusters, could be essential for the correct conformation of the fulllength protein, at least in mammalian cells. We prepared cytosolic fractions, immunoprecipitated endogenous IOP1, and examined the immunoprecipitates by Western blotting using anti-IscA1 antibodies.
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