Fe-S Cluster (Fe- + cluster)

Distribution by Scientific Domains

Selected Abstracts

Insights into the function of the WhiB-like protein of mycobacteriophage TM4 , a transcriptional inhibitor of WhiB2

Jan Rybniker
Summary WhiB-like proteins of actinomycetes are known to co-ordinate iron-sulfur (Fe-S) clusters and are believed to have regulatory functions in many essential bacterial processes. The systematic determination of the genome sequences of mycobacteriophages has revealed the presence of several whiB -like genes in these viruses. Here we focussed on the WhiB-like protein of mycobacteriophage TM4, WhiBTM4. We provide evidence that this viral protein is capable of co-ordinating a Fe-S cluster. The UV-visible absorption spectra obtained from freshly purified and reconstituted WhiBTM4 were consistent with the presence of an oxygen sensitive [2Fe-2S] cluster. Expression of WhiBTM4 in the mycobacterial host led to hindered septation resembling a WhiB2 knockout phenotype whereas basal expression of WhiBTM4 led to superinfection exclusion. The quantification of mRNA-levels during phage infection showed that whiBTM4 is a highly transcribed early phage gene and a dominant negative regulator of WhiB2. Strikingly, both apo-WhiB2 of Mycobacterium tuberculosis and apo-WhiBTM4 were capable of binding to the conserved promoter region upstream of the whiB2 gene indicating that WhiB2 regulates its own synthesis which is inhibited in the presence of WhiBTM4. Thus, we provide substantial evidence supporting the hypothesis of viral and bacterial WhiB proteins being important Fe-S containing transcriptional regulators with DNA-binding capability. [source]

Studies of Iron-Sulfur Covalency in the Model System and Proteins

Xiu-Juan Qin
Abstract It was found that the highly covalent nature of the metal-ligand interactions in the Fe-S cluster clearly played an important role in determining the reactivity of the sites. A semi-empirical model, based on the Phillips theory of bonding was developed for quantitative explanation of covalency in Fe-S cluster, showing that Mossbauer spectroscopy and electronic absorption spectroscopy provided the direct experimental probe of covalency of Fe-S4 clusters. [source]

IscR acts as an activator in response to oxidative stress for the suf operon encoding Fe-S assembly proteins

Won-Sik Yeo
Summary In Escherichia coli, Fe-S clusters are assembled by gene products encoded from the isc and suf operons. Both the iscRSUA and sufABCDSE operons are induced highly by oxidants, reflecting an increased need for providing and maintaining Fe-S clusters under oxidative stress conditions. Three cis -acting oxidant-responsive elements (ORE-I, II, III) in the upstream of the sufA promoter serve as the binding sites for OxyR, IHF and an uncharacterized factor respectively. Using DNA affinity fractionation, we isolated an ORE-III-binding factor that positively regulates the suf operon in response to various oxidants. MALDI-TOF mass analysis identified it with IscR, known to serve as a repressor of the iscRSUA gene expression under anaerobic condition as a [2Fe-2S]-bound form. The iscR null mutation abolished ORE-III-binding activity in cell extracts, and caused a significant decrease in the oxidant induction of sufA in vivo. OxyR and IscR contributed almost equally to activate the sufA operon in response to oxidants. Purified IscR that lacked Fe-S cluster bound to the ORE-III site and activated transcription from the sufA promoter in vitro. Mutations in Fe-S-binding sites of IscR enabled sufA activation in vivo and in vitro. These results support a model that IscR in its demetallated form directly activates sufA transcription, while it de-represses isc operon, under oxidative stress condition. [source]

Biochemical and genetic bases of dehalorespiration

Taiki Futagami
Abstract Some anaerobic bacteria can efficiently eliminate one or more halide atoms from halogenated compounds such as chlorophenols and chloroethenes through reductive dehalogenation. During this process, the bacteria utilize halogenated compounds as the terminal electron acceptors in their anaerobic respiration, called dehalorespiration, to yield energy for growth. Currently the genera of Desulfitobacterium and Dehalococcoides occupy the major part of the dehalorespiring isolates. The former can acquire energy not only by dehalorespiration but also by other respirations utilizing organic compounds and metals. In sharp contrast, the latter is specialized in dehalorespiration and plays a crucial role in the detoxification of chlorinated compounds in nature. From these bacteria, various reductive dehalogenases, which catalyze the dehalogenation reaction, were purified and their corresponding genes were identified. Most reductive dehalogenases exhibit similar features such as the presences of a Tat (twin arginine translocation) signal sequence, two Fe-S clusters, and a corrinoid cofactor. Some of dehalogenase-encoding genes are found to be flanked by insertion sequences. Thus, dehalogenase genes act as a catabolic transposon, and genetic rearrangements mediated by transposable elements occur well in dehalorespirers. Moreover, the genome sequences of some dehalorespiring bacteria provide many insights into the mechanism of dehalorespiration and the evolution of a dehalogenase gene. 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 1,12; 2008: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20134 [source]