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Journal of Bacteriology, March 2009, p. 1490-1497, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01469-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Archaeal ApbC/Nbp35 Homologs Function as Iron-Sulfur Cluster Carrier Proteins{triangledown} ,{dagger}

Jeffrey M. Boyd,1 Randy M. Drevland,2 Diana M. Downs,1 and David E. Graham2,3*

Department of Bacteriology, University of Wisconsin, Madison, Madison, Wisconsin 53706,1 Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712,2 Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 787123

Received 17 October 2008/ Accepted 19 December 2008

Iron-sulfur clusters may have been the earliest catalytic cofactors on earth, and most modern organisms use them extensively. Although members of the Archaea produce numerous iron-sulfur proteins, the major cluster assembly proteins found in the Bacteria and Eukarya are not universally conserved in archaea. Free-living archaea do have homologs of the bacterial apbC and eukaryotic NBP35 genes that encode iron-sulfur cluster carrier proteins. This study exploits the genetic system of Salmonella enterica to examine the in vivo functionality of apbC/NBP35 homologs from three archaea: Methanococcus maripaludis, Methanocaldococcus jannaschii, and Sulfolobus solfataricus. All three archaeal homologs could correct the tricarballylate growth defect of an S. enterica apbC mutant. Additional genetic studies showed that the conserved Walker box serine and the Cys-X-X-Cys motif of the M. maripaludis MMP0704 protein were both required for function in vivo but that the amino-terminal ferredoxin domain was not. MMP0704 protein and an MMP0704 variant protein missing the N-terminal ferredoxin domain were purified, and the Fe-S clusters were chemically reconstituted. Both proteins bound equimolar concentrations of Fe and S and had UV-visible spectra similar to those of known [4Fe-4S] cluster-containing proteins. This family of dimeric iron-sulfur carrier proteins evolved before the archaeal and eukaryal lineages diverged, representing an ancient mode of cluster assembly.

* Corresponding author. Mailing address: Department of Chemistry and Biochemistry, University of Texas at Austin, 1 University Station A5300, Austin, TX 78712. Phone: (512) 471-4491. Fax: (512) 471-8696. E-mail: degraham{at}mail.utexas.edu

{triangledown} Published ahead of print on 29 December 2008.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, March 2009, p. 1490-1497, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01469-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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