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IscR of Rhodobacter sphaeroides functions as repressor of genes for iron-sulphur metabolism and represents a new type of iron-sulphur binding protein

ABSTRACT: Iron-sulphur (Fe-S) clusters are ensembles of iron and sulphide centres. They are found in all life forms and are important components of many enzymes involved in diverse cellular processes, including respiration, DNA synthesis or gene regulation. However, the increase in oxygen after the emergence of oxygenic photosynthesis created a threat to Fe–S proteins and, consequently, to the organisms relying on them. Therefore, bacteria have evolved mechanisms to maintain a precise intracellular iron concentration. A major role of IscR in R. sphaeroides iron dependent regulation was suggested in a bioinformatic study , which predicted a binding site in the upstream regions of several iron uptake genes. Most known IscR proteins have Fe-S clusters featuring (Cys)3(His)1 ligation. However, IscR proteins from Rhodobacteraceae harbour only one Cys residue and it was considered unlikely that they can ligate an Fe-S cluster. In this study, the role of R. sphaeroides IscR as transcriptional regulator and sensor of the Fe-S cluster status of the cell was analysed. The results provide evidence that R. sphaeroides IscR functions as transcriptional repressor of genes involved in iron metabolism by binding to the predicted DNA binding motif. Furthermore, IscR possesses a unique Fe-S cluster ligation scheme with only a single cysteine involved.

ORGANISM(S): Cereibacter sphaeroides 2.4.1

PROVIDER: GSE65537 | GEO | 2015/02/03

SECONDARY ACCESSION(S): PRJNA274297

REPOSITORIES: GEO

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Project description:High-affinity iron (Fe) scavenging compounds, or siderophores, are widely employed by soil bacteria to survive scarcity in bioavailable Fe. Siderophore biosynthesis relies on cellular carbon metabolism, despite reported decrease in both carbon uptake and Fe-containing metabolic proteins in Fe-deficient cells. Given this paradox, the metabolic network required to sustain the Fe-scavenging strategy is poorly understood. Here, through multiple 13C-metabolomics experiments with Fe-replete and Fe-limited cells, we uncover how soil Pseudomonas species reprogram their metabolic pathways to prioritize siderophore biosynthesis. Across the three species investigated (Pseudomonas putida KT2440, Pseudomonas protegens Pf-5, and Pseudomonas putida S12), siderophore secretion is higher during growth on gluconeogenic substrates than during growth on glycolytic substrates. In response to Fe limitation, we capture decreased flux toward the tricarboxylic acid (TCA) cycle during the metabolism of glycolytic substrates but, due to carbon recycling to the TCA cycle via enhanced anaplerosis, the metabolism of gluconeogenic substrates results in an increase in both siderophore secretion (up to threefold) and Fe extraction (up to sixfold) from soil minerals. During simultaneous feeding on the different substrate types, Fe deficiency triggers a hierarchy in substrate utilization, which is facilitated by changes in protein abundances for substrate uptake and initial catabolism. Rerouted metabolism further promotes favorable fluxes in the TCA cycle and the gluconeogenesis-anaplerosis nodes, despite decrease in several proteins in these pathways, to meet carbon and energy demands for siderophore precursors in accordance with increased proteins for siderophore biosynthesis. Hierarchical carbon metabolism thus serves as a critical survival strategy during the metal nutrient deficiency. Data availability:The proteomics data have been deposited into the ProteomeXchange Consortium via the PRIDE partner repository with the data set identifier <a href='https://www.ebi.ac.uk/pride/archive/projects/PXD013605' rel='noopener noreferrer' target='_blank'>PXD013605</a>.

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IscR of Rhodobacter sphaeroides functions as repressor of genes for iron-sulphur metabolism and represents a new type of iron-sulphur binding protein

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