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J Struct Biol. 2020 Mar 6:107491. doi: 10.1016/j.jsb.2020.107491. [Epub ahead of print]

ISCU interacts with NFU1, and ISCU[4Fe-4S] transfers its Fe-S cluster to NFU1 leading to the production of holo-NFU1.

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Biochemistry Department, University of Wisconsin-Madison, Madison, WI 53706, USA.


NFU1 is a late-acting factor in the biogenesis of human mitochondrial iron-sulfur proteins. Mutations in NFU1 are associated with genetic diseases such as multiple mitochondrial dysfunctions syndrome 1 (MMDS1) that involve defects in mitochondrial [4Fe-4S] proteins. We present results from NMR spectroscopy, small angle X-ray scattering, size exclusion chromatography, and isothermal titration calorimetry showing that the structured conformer of human ISCU binds human NFU1. The dissociation constant determined by ITC is Kd = 1.1 ± 0.2 μM. NMR and SAXS studies led to a structural model for the complex in which the cluster binding region of ISCU interacts with two α-helices in the C-terminal domain of NFU1. In vitro experiments demonstrate that ISCU[4Fe-4S] transfers its Fe-S cluster to apo-NFU1, in the absence of a chaperone, leading to the assembly of holo-NFU1. By contrast, the cluster of ISCU[2Fe-2S] remains bound to ISCU in the presence of apo-NFU1.


ISCU; Iron-sulfur cluster biogenesis; NFU1; NMR; Protein-protein interactions; Small angle X-ray scattering

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Conflict of interest statement

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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