Saio Tomohide, Kumeta Hiroyuki, Ogura Kenji, Yokochi Masashi, Asayama Munehiko, Katoh Shizue, Katoh Etsuko, Teshima Keizo, Inagaki Fuyuhiko
Laboratory of Structural Biology, Graduate School of Pharmaceutical Science, Hokkaido University, Sapporo, Hokkaido, Japan.
J Biochem. 2007 Jul;142(1):113-21. doi: 10.1093/jb/mvm120. Epub 2007 Jun 1.
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.
OsCnfU-1A是一种叶绿体类型的类Nfu蛋白，由具有高度序列同源性的串联重复序列组成。该蛋白的结构域I而非结构域II具有一个C-X-X-C基序，被认为可组装铁硫簇。在此我们报道了OsCnfU-1A结构域I（73-153）的溶液结构。尽管OsCnfU-1A结构域I在结构上与OsCnfU-1A结构域II（154-226）相似，但这两个结构域的静电表面电势不同。结构域I具有酸性表面，而结构域II的表面主要呈碱性。对OsCnfU-1A结构域I和结构域II与铁氧还蛋白进行的化学位移扰动研究表明，结构域I中的化学位移变化可忽略不计，而在结构域II中观察到了更大的化学位移变化。化学位移变化较大的残基位于结构域II的碱性表面。鉴于铁氧还蛋白主要带负电荷，我们提出以下假设：首先，铁硫簇在结构域I上组装。其次，结构域II与铁氧还蛋白相互作用，从而将结构域I拴在靠近铁氧还蛋白的位置。最后，结构域I将铁硫簇转移至铁氧还蛋白。因此，结构域II促进了铁硫簇从结构域I到铁氧还蛋白的高效转移。
