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author:("Tan, guoyang")
1.  Competition of zinc ion for the [2Fe–2S] cluster binding site in the diabetes drug target protein mitoNEET 
Human mitochondrial protein mitoNEET is a novel target of type II diabetes drug pioglitazone, and contains a redox active [2Fe–2S] cluster that is hosted by a unique ligand arrangement of three cysteine and one histidine residues. Here we report that zinc ion can compete for the [2Fe–2S] cluster binding site in human mitoNEET and potentially modulate the physiological function of mitoNEET. When recombinant mitoNEET is expressed in Escherichia coli cells grown in M9 minimal media, purified mitoNEET contains very little or no iron–sulfur clusters. Addition of exogenous iron or zinc ion in the media produces mitoNEET bound with a [2Fe–2S] cluster or zinc, respectively. Mutations of the amino acid residues that hosting the [2Fe–2S] cluster in mitoNEET diminish the zinc binding activity, indicating that zinc ion and the [2Fe–2S] cluster may share the same binding site in mitoNEET. Finally, excess zinc ion effectively inhibits the [2Fe–2S] cluster assembly in mitoNEET in E. coli cells, suggesting that zinc ion may impede the function of mitoNEET by blocking the [2Fe–2S] cluster assembly in the protein.
doi:10.1007/s10534-012-9580-4
PMCID: PMC3822609  PMID: 22945239
Human mitoNEET; Type II diabetes drug pioglitazone; Iron–sulfur cluster; Zinc binding
2.  Escherichia coli topoisomerase I is an iron and zinc binding protein 
Escherichia coli topoisomerase I (TopA) cleaves and rejoins one strand of double-stranded DNA to relax the negatively supercoiled DNA. Structurally, TopA contains an N-terminal catalytic fragment and a C-terminal zinc-binding region that is required for relaxation of the negatively supercoiled DNA. Here we report that E. coli TopA is an iron and zinc binding protein. The UV–Vis absorption measurements and metal content analyses reveal that TopA purified from E. coli cells grown in the rich LB medium contains both iron and zinc. However, TopA purified from E. coli cells grown in the M9 minimal medium has negligible amounts of zinc or iron and no topoisomerase activity. Nevertheless, supplement of exogenous zinc or iron in E. coli cells grown in the M9 minimal medium produces the zinc- or iron-bound TopA, respectively. Whereas the zinc-bound TopA is fully active to relax the negatively super-coiled DNA, the iron-bound TopA has little or no enzyme activity. Furthermore, excess iron in the M9 minimal medium is able to compete with the zinc binding in TopA in E. coli cells and attenuate the topoisomerase activity, suggesting that E. coli TopA may be modulated by iron and zinc binding in vivo.
doi:10.1007/s10534-011-9425-6
PMCID: PMC3123405  PMID: 21347852
Topoisomerase I; Zinc; Iron; Metalloprotein
3.  Reduction of Mitoferrin Results in Abnormal Development and Extended Lifespan in Caenorhabditis elegans 
PLoS ONE  2012;7(1):e29666.
Iron is essential for organisms. It is mainly utilized in mitochondria for biosynthesis of iron-sulfur clusters, hemes and other cofactors. Mitoferrin 1 and mitoferrin 2, two homologues proteins belonging to the mitochondrial solute carrier family, are required for iron delivery into mitochondria. Mitoferrin 1 is highly expressed in developing erythrocytes which consume a large amount of iron during hemoglobinization. Mitoferrin 2 is ubiquitously expressed, whose functions are less known. Zebrafish with mitoferrin 1 mutation show profound hypochromic anaemia and erythroid maturation arrests, and yeast with defects in MRS3/4, the counterparts of mitoferrin 1/2, has low mitochondrial iron levels and grows poorly by iron depletion. Mitoferrin 1 expression is up-regulated in yeast and mouse models of Fiedreich's ataxia disease and in human cell culture models of Parkinson disease, suggesting its involvement in the pathogenesis of diseases with mitochondrial iron accumulation. In this study we found that reduced mitoferrin levels in C. elegans by RNAi treatment causes pleiotropic phenotypes such as small body size, reduced fecundity, slow movement and increased sensitivity to paraquat. Despite these abnormities, lifespan was increased by 50% to 80% in N2 wild type strain, and in further studies using the RNAi sensitive strain eri-1, more than doubled lifespan was observed. The pathways or mechanisms responsible for the lifespan extension and other phenotypes of mitoferrin RNAi worms are worth further study, which may contribute to our understanding of aging mechanisms and the pathogenesis of iron disorder related diseases.
doi:10.1371/journal.pone.0029666
PMCID: PMC3256167  PMID: 22253756
4.  In vivo Evidence for the Iron Binding Activity of an Iron-Sulfur Cluster Assembly Protein IscA in Escherichia coli 
The Biochemical journal  2010;432(3):429-436.
SYNOPSIS
IscA is a key member of the iron-sulfur cluster assembly machinery in prokaryotic and eukaryotic organisms; however, the physiological function of IscA still remains elusive. Here we report the in vivo evidence demonstrating the iron binding activity of IscA in Escherichia coli cells. Supplement of exogenous iron (1μM) in the M9 minimal medium is sufficient to maximize the iron binding in IscA expressed in E. coli cells under aerobic growth conditions. In contrast, IscU, an iron-sulfur cluster assembly scaffold protein, or CyaY, a bacterial frataxin homologue, fails to bind any iron in E. coli cells under the same experimental conditions. Interestingly, the strong iron binding activity of IscA is greatly diminished in E. coli cells under anaerobic growth conditions. Additional studies reveal that oxygen in medium promotes the iron binding in IscA and that the iron binding in IscA in turn prevents formation of biologically inaccessible ferric hydroxide under aerobic conditions. Consistent with the differential iron binding activity of IscA under aerobic and anaerobic conditions, we find that IscA and its paralog SufA are essential for the iron-sulfur cluster assembly in E. coli cells under aerobic growth conditions but not under anaerobic growth conditions. The results provide the in vivo evidence that IscA may act as an iron chaperone for the biogenesis of iron-sulfur clusters in E. coli cells under aerobic conditions.
doi:10.1042/BJ20101507
PMCID: PMC2992610  PMID: 20942799
Iron-sulfur cluster biogenesis; human IscA homologue; intracellular iron content
5.  Iron Binding Activity of Human Iron-Sulfur Cluster Assembly Protein hIscA-1 
The Biochemical journal  2010;428(1):125-131.
SYNOPSIS
A human homologue of the iron-sulfur cluster assembly protein IscA (hIscA1) has been cloned and expressed in Escherichia coli cells. The UV-visible absorption and EPR (electron paramagnetic resonance) measurements reveal that hIscA1 purified from E. coli cells contains a mononuclear iron center and that the iron binding in hIscA1 expressed in E. coli cells can be further modulated by the iron content in the cell growth medium. Additional studies show that purified hIscA1 binds iron with an iron association constant of approx. 2.0 × 1019 M−1, and that the iron-bound hIscA1 is able to provide the iron for the iron-sulfur cluster assembly in a proposed scaffold protein IscU of E. coli in vitro. The complementation experiments indicate that hIscA1 can partially substitute for IscA in restoring the cell growth of E. coli in the M9 minimal medium under aerobic conditions. The results suggest that human IscA1, like E. coli IscA, is an iron binding protein that may act as an iron chaperone for biogenesis of iron-sulfur clusters.
doi:10.1042/BJ20100122
PMCID: PMC2878720  PMID: 20302570
Iron-sulfur cluster biogenesis; human IscA homologue; intracellular iron content
6.  IscA/SufA Paralogs Are Required for the [4Fe-4S] Cluster Assembly in Enzymes of Multiple Physiological Pathways in Escherichia coli under Aerobic Growth Conditions 
The Biochemical journal  2009;420(3):463-472.
Synopsis
IscA/SufA paralogs are the members of the iron-sulfur cluster assembly machinery in Escherichia coli. While deletion of either IscA or SufA has only a mild effect on cell growth, deletion of both IscA and SufA results in a null-growth phenotype in minimal medium under aerobic growth conditions. Here we report that cell growth of the iscA/sufA double mutant (E. coli strain in which both iscA and sufA had been in-frame-deleted) can be partially restored by supplementing with BCAAs (branched-chain amino acids) and thiamin. We further demonstrate that deletion of IscA/SufA paralogs blocks the [4Fe-4S] cluster assembly in IlvD (dihydroxyacid dehydratase) of the BCAA biosynthesis pathway in E. coli cells under aerobic conditions and that addition of the iron-bound IscA/SufA efficiently promotes the [4Fe-4S] cluster assembly in IlvD and restores the enzyme activity in vitro, suggesting that IscA/SufA may act as an iron donor for the [4Fe-4S] cluster assembly under aerobic conditions. Additional studies reveal that IscA/SufA are also required for the [4Fe-4S] cluster assembly in protein ThiC of the thiamin biosynthesis pathway, aconitase B of the citrate acid cycle, and endonuclease III of the DNA base excision repair pathway in E. coli under aerobic conditions. Nevertheless, deletion of IscA/SufA does not significantly affect the [2Fe-2S] cluster assembly in the redox transcription factor SoxR, ferredoxin, and the siderophore-iron reductase FhuF. The results suggest that the biogenesis of the [4Fe-4S] clusters and the [2Fe-2S] clusters may have distinct pathways and that IscA/SufA paralogs are essential for the [4Fe-4S] cluster assembly, but are dispensable for the [2Fe-2S] cluster assembly in E. coli under aerobic conditions.
doi:10.1042/BJ20090206
PMCID: PMC2776711  PMID: 19309314
aconitase; branched-chain amino acids; dihydroxyacid dehydratase; iron-sulfur clusters; IscA/SufA paralogs; thiamin
7.  Reactivity of Nitric Oxide with the [4Fe-4S] Cluster of Dihydroxyacid Dehydratase from Escherichia coli 
The Biochemical journal  2009;417(3):783-789.
Synopsis
Although the NO (nitric oxide)-mediated modification of iron-sulfur proteins has been well documented in bacteria and mammalian cells, specific reactivity of NO with iron-sulfur proteins still remains elusive. Here, we report the first kinetic characterization of the reaction between NO and iron-sulfur clusters in protein using the Escherichia coli dihydroxyacid dehydratase (IlvD) [4Fe-4S] cluster as an example. Combining a sensitive NO electrode with EPR (electron paramagnetic resonance) spectroscopy and an enzyme activity assay, we demonstrate that NO is rapidly consumed by the IlvD [4Fe-4S] cluster with the concomitant formation of the IlvD-bound DNIC (dinitrosyl iron complex) and inactivation of the enzyme activity under anaerobic conditions. The rate constant for the initial reaction between NO and the IlvD [4Fe-4S] cluster is estimated to be (7.0±2.0) × 106M-2s-1 at 25°C, which is approx. 2-3 times faster than that of the NO autooxidation by O2 in aqueous solution. Addition of reduced glutathione (GSH) fails to prevent the NO-mediated modification of the IlvD [4Fe-4S] cluster regardless of the O2 presence in the medium, further suggesting that NO is more reactive with the IlvD [4Fe-4S] cluster than with GSH or O2. Purified aconitase B [4Fe-4S] cluster from E. coli has an almost identical NO reactivity as the IlvD [4Fe-4S] cluster. However, the reaction between NO and the endonuclease III [4Fe-4S] cluster is relatively slow, apparently because the [4Fe-4S] cluster in endonuclease III is less accessible to solvent than those in IlvD and aconitase B. When E. coli cells containing recombinant IlvD, aconitase B or endonuclease III are exposed to NO using the Silastic tubing NO delivery system under aerobic and anaerobic conditions, the [4Fe-4S] clusters in IlvD and aconitase B, but not in endonuclease III, are efficiently modified forming the protein-bound DNICs, confirming that NO has a higher reactivity with the [4Fe-4S] clusters in IlvD and aconitase B than with O2 or GSH. The results suggest that the iron-sulfur clusters in proteins such as IlvD and aconitase B may constitute the primary targets of the NO cytotoxicity under both aerobic and anaerobic conditions.
doi:10.1042/BJ20081423
PMCID: PMC2706667  PMID: 18945212
dihydroxyacid dehydratase; dinitrosyl-iron complex; iron-sulfur proteins; nitric oxide

Results 1-7 (7)