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Conserved system for assembly of Fe/S clusters and their insertion into proteins

Mitochondria contain a complex system for assembly of Fe/S metal centers and their insertion into proteins. A specialized J-protein/ Hsp70 molecular chaperone pair is a critical part of this system, interacting specifically with the scaffold protein on which clusters are first built and facilitating cluster transfer. We aim to unravel the mechanism of action of this dedicated chaperone system and the regulation of expression of its components.

In cells Fe/S clusters are not spontaneously formed. Rather a complex assembly system exists to facilitate Fe/S cluster insertion into proteins in all cells. We are using yeast mitochondria as a model system to better understand Fe/S center biogenesis and mitochondrial iron homeostasis. An Fe/S cluster is transiently assembled on a scaffold protein, called Isu, prior to transfer to the recipient protein. Additional proteins act as sulfur and iron donors. In addition, an Hsp70 chaperone system, consisting of the Hsp70 Ssq1, the J-protein Jac1 and the nucleotide release factor Mge1, is required for efficient Fe/S cluster biogenesis. Both in vivo and in vitro evidence supports a role for the chaperones in transfer of the cluster to recipient proteins.

Questions we are addressing include:

  • The role of the J-protein/Hsp70 system in Fe/S protein biogenesis.  An interplay between yeast genetics and the biochemical analysis of purified components is being used to understand chaperone function in Fe-S center biogenesis.  How does the J-protein Jac1 bind Isu to initiate chaperone activity? How is the expression of the scaffold Isu linked to chaperone function?
  • The frataxin connection. The human frataxin gene is associated with the disease Freidrich’s ataxia, the most common inherited form of ataxia. Deletion of the yeast frataxin homolog, YFH1, has cellular effects similar to those found in cells of patients with Freidrich’s ataxia, a decrease in the amount of Fe/S clusters and increase iron levels in mitochondria. We are analyzing the function of Yfh1, particularly in Fe/S cluster biogenesis.
  • The evolution of specialized Hsp70s for Fe/S cluster biogenesis. The specialized J-protein that functions in Fe/S cluster biogenesis is highly conserved across eukaryotes, as well as some prokaryotes. A specialized Hsp70 is found in only a small set of fungi, indicating that the general Hsp70 of the mitochondrial matrix functions in Fe/S cluster biogenesis in most species. This history allows us a unique opportunity to study the evolution of specialization of a molecular chaperone machine.

Selected Craig lab publications:

Andrew, A.J., Song,J-Y., Schilke, B., and Craig, E.A. (2008) Postranslational Regulation of the Scaffold for FE-S cluster Biogenesis, Isu. Mol. Biol. Cell. 19:5259-5266. [PDF]

Wang T, Craig, EA. (2008) Binding of Yeast Frataxin to the Scaffold for Fe-S Cluster Biogenesis, Isu. J Biol Chem. 283:12674-9. [PDF]

Schilke B, Williams B, Knieszner H, Pukszta S, D'Silva P, Craig EA, (2006) Marszalek J. Evolution of mitochondrial chaperones utilized in Fe-S cluster biogenesis. Curr Biol. 16:1660-5. [PDF]

Andrew AJ, Dutkiewicz R, Knieszner H, Craig EA, Marszalek J. (2006) Characterization of the interaction between the J-protein Jac1p and the scaffold for Fe-S cluster biogenesis, Isu1p.  J Biol Chem. 2006 May 26;281(21):14580-7. [PDF]

Aloria K, Schilke B, Andrew A, Craig EA. (2004) Iron-induced oligomerization of yeast frataxin homologue Yfh1 is dispensable in vivo. EMBO Rep. Nov;5(11):1096-101. [PDF]

Dutkiewicz R, Schilke B, Cheng S, Knieszner H, Craig EA, Marszalek J. (2004) Sequence specific interactions between mitochondrial Fe/S scaffold protein Isu1 and Hsp70 Ssq1 is essential for their in vivo function. J Biol Chem. 279:29167-74. [PDF]

Voisine, C, Cheng, Y, Ohlson, M, Schilke, B, Hoff, K, Beinert, H, Marszalek, J and Craig, EA (2001) Jac1, a mitochondrial J-type chaperone involved in biogenesis of Fe/S clusters in S. cerevisiae. Proc. Natl. Acad. Sci (USA). 98:1483-1488. [PDF]