In vivo iron–sulfur cluster formation
- Estella C. Raulfs*,
- Ina P. O'Carroll*,
- Patricia C. Dos Santos,
- Mihaela-Carmen Unciuleac†, and
- Dennis R. Dean‡
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Edited by Brian M. Hoffman, Northwestern University, Evanston, IL, and approved May 6, 2008
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↵*E.C.R. and I.P.O. contributed equally to this work. (received for review April 1, 2008)
Abstract
It has been proposed that iron–sulfur [Fe-S] clusters destined for the maturation of [Fe-S] proteins can be preassembled on a molecular scaffold designated IscU. In the present article, it is shown that production of the intact Azotobacter vinelandii [Fe-S] cluster biosynthetic machinery at levels exceeding the amount required for cellular maturation of [Fe-S] proteins results in the accumulation of: (i) apo-IscU, (ii) an oxygen-labile [2Fe-2S] cluster-loaded form of IscU, and (iii) IscU complexed with the S-delivery protein, IscS. It is suggested that these species represent different stages of the [Fe-S] cluster assembly process. Substitution of the IscU Asp39 residue by Ala results in the in vivo trapping of a stoichiometric, noncovalent, nondissociating IscU–IscS complex that contains an oxygen-resistant [Fe-S] species. In aggregate, these results validate the scaffold hypothesis for [Fe-S] cluster assembly and indicate that in vivo [Fe-S] cluster formation is a dynamic process that involves the reversible interaction of IscU and IscS.
Footnotes
- ‡To whom correspondence should be sent. E-mail: deandr{at}vt.edu
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Author contributions: E.C.R., I.P.O., P.C.D.S., and D.R.D. designed research; E.C.R., I.P.O., and M.-C.U. performed research; E.C.R., I.P.O., P.C.D.S., and D.R.D. analyzed data; and E.C.R., I.P.O., P.C.D.S., and D.R.D. wrote the paper.
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↵ †Present address: Molecular Biology Program, Sloan–Kettering Institute, New York, NY 10021.
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The authors declare no conflict of interest.
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This article is a PNAS Direct Submission.
- © 2008 by The National Academy of Sciences of the USA
