Journal of Biochemistry Advance Access originally published online on June 1, 2007
Journal of Biochemistry 2007 142(1):113-121; doi:10.1093/jb/mvm120
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© 2007 The Japanese Biochemical Society.
The Cooperative Role of OsCnfU-1A Domain I and Domain II in the Iron–Sulphur Cluster Transfer Process as Revealed by NMR
1Laboratory of Structural Biology, Graduate School of Pharmaceutical Science, Hokkaido University, Sapporo, Hokkaido, Japan; 2Laboratory of Molecular Genetics, College of Agriculture, Ibaraki University, Ami 3-21-1, Ibaraki 300-0393, Japan; 3Biochemistry Department, National Institute of Agrobiological Science, Tsukuba, Ibaraki 305-8602, Japan; and 4Faculty of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima 739-8521, Japan
*To whom correspondence should be addressed: Tel.: +81-11-706-9011, Fax: +81-11-706-9012, E-mail: finagaki{at}pharm.hokudai.ac.jp
Received March 7, 2007; Accepted May 6, 2007
| Abstract |
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OsCnfU-1A is a chloroplast-type Nfu-like protein that consists of tandem repeats sharing high sequence homology. Domain I of this protein, but not domain II, has a C-X-X-C motif that is thought to assemble an iron–sulphur cluster. Herein we report the solution structure of OsCnfU-1A domain I (73–153). Although OsCnfU-1A domain I is structurally similar to OsCnfU-1A domain II (154–226), the electrostatic surface potential of the 2 domains differs. Domain I has an acidic surface, whereas that of domain II is predominantly basic. Chemical shift perturbation studies on OsCnfU-1A domain I and domain II with ferredoxin revealed negligible chemical shift changes in domain I, whereas much larger chemical shift changes were observed in domain II. The residues with larger chemical shift changes were located on the basic surface of domain II. Considering that ferredoxin is predominantly negatively charged, we propose the following hypothesis: First, an iron–sulphur cluster is assembled on domain I. Next, domain II interacts with the ferredoxin, thus tethering domain I close to the ferredoxin. Finally, domain I transfers the iron–sulphur cluster to the ferredoxin. Thus, domain II facilitates the efficient transfer of the iron–sulphur cluster from domain I to the ferredoxin.
Key Words: cell-free protein synthesis, Fe–S cluster, Nfu-like protein, NMR structure, Oryza sativa
Abbreviations: CnfU, C-termainal domain of NifU; [Fe-S], iron-sulphur; FNR, ferredoxin-NADP+ reductase; HIRA, histone cell-cycle regulation defective homology A; HIRIP5, HIRA-interacting protein 5; HSQC, heteronuclear single quantum correlation; IscU, iron-sulphur cluster assembly protein U; NOESY, nuclear overhauser effect spectroscopy; RMSD, root mean square deviation; SiR, sulphite reductase
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