title: Characterization of iron-sulfur cluster assembly protein IscA from Acidithiobacillus ferrooxidans.
abstract: IscA is a key member of the iron-sulfur cluster assembly machinery found in bacteria and eukaryotes, but the mechanism of its function in the biogenesis of iron-sulfur cluster remains elusive. In this paper, we demonstrate that Acidithiobacillus ferrooxidans IscA is a [4Fe-4S] cluster binding protein, and it can bind iron in the presence of DTT with an apparent iron association constant of 4·10(20) M(-1). The iron binding in IscA can be promoted by oxygen through oxidizing ferrous iron to ferric iron. Furthermore, we show that the iron bound form of IscA can be converted to iron-sulfur cluster bound form in the presence of IscS and L-cysteine in vitro. Substitution of the invariant cysteine residues Cys35, Cys99, or Cys101 in IscA abolishes the iron binding activity of the protein; the IscA mutants that fail to bind iron are unable to assemble the iron-sulfur clusters. Further studies indicate that the iron-loaded IscA could act as an iron donor for the assembly of iron-sulfur clusters in the scaffold protein IscU in vitro. Taken together, these findings suggest that A. ferrooxidans IscA is not only an iron-sulfur protein, but also an iron binding protein that can act as an iron donor for biogenesis of iron-sulfur clusters.
authors.affiliation: College of Environmental Science and Engineering, Donghua University, Shanghai, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Qian
authors.forename: Chunli
authors.initials: C
authors.lastname: Zheng
authors.forename: Jianshe
authors.initials: J
authors.lastname: Liu
mesh_terms: D042763:Acidithiobacillus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D007501:Iron / Q000378:metabolism; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D013455:Sulfur / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D007506:Iron-Sulfur Proteins; D013455:Sulfur; D007501:Iron