| Autor: |
Pellicer Martinez MT; Centre for Molecular and Structural Biochemistry , School of Chemistry , University of East Anglia , Norwich Research Park , Norwich , NR4 7TJ , UK . Email: n.le-brun@uea.ac.uk ; ; Tel: +44 1603 592699., Martinez AB; School of Biological Sciences , University of East Anglia , Norwich Research Park , Norwich , NR4 7TJ , UK., Crack JC; Centre for Molecular and Structural Biochemistry , School of Chemistry , University of East Anglia , Norwich Research Park , Norwich , NR4 7TJ , UK . Email: n.le-brun@uea.ac.uk ; ; Tel: +44 1603 592699., Holmes JD; Centre for Molecular and Structural Biochemistry , School of Chemistry , University of East Anglia , Norwich Research Park , Norwich , NR4 7TJ , UK . Email: n.le-brun@uea.ac.uk ; ; Tel: +44 1603 592699., Svistunenko DA; School of Biological Sciences , University of Essex , Wivenhoe Park , Colchester CO4 3SQ , UK., Johnston AWB; School of Biological Sciences , University of East Anglia , Norwich Research Park , Norwich , NR4 7TJ , UK., Cheesman MR; Centre for Molecular and Structural Biochemistry , School of Chemistry , University of East Anglia , Norwich Research Park , Norwich , NR4 7TJ , UK . Email: n.le-brun@uea.ac.uk ; ; Tel: +44 1603 592699., Todd JD; School of Biological Sciences , University of East Anglia , Norwich Research Park , Norwich , NR4 7TJ , UK., Le Brun NE; Centre for Molecular and Structural Biochemistry , School of Chemistry , University of East Anglia , Norwich Research Park , Norwich , NR4 7TJ , UK . Email: n.le-brun@uea.ac.uk ; ; Tel: +44 1603 592699. |
| Abstrakt: |
Rhizobial iron regulator A (RirA) is a global regulator of iron homeostasis in many nitrogen-fixing Rhizobia and related species of α-proteobacteria. It belongs to the widespread Rrf2 super-family of transcriptional regulators and features three conserved Cys residues that characterise the binding of an iron-sulfur cluster in other Rrf2 family regulators. Here we report biophysical studies demonstrating that RirA contains a [4Fe-4S] cluster, and that this form of the protein binds RirA-regulated DNA, consistent with its function as a repressor of expression of many genes involved in iron uptake. Under low iron conditions, [4Fe-4S] RirA undergoes a cluster conversion reaction resulting in a [2Fe-2S] form, which exhibits much lower affinity for DNA. Under prolonged low iron conditions, the [2Fe-2S] cluster degrades to apo-RirA, which does not bind DNA and can no longer function as a repressor of the cell's iron-uptake machinery. [4Fe-4S] RirA was also found to be sensitive to O 2 , suggesting that both iron and O 2 are important signals for iron metabolism. Consistent with this, in vivo data showed that expression of RirA-regulated genes is also affected by O 2 . These data lead us to propose a novel regulatory model for iron homeostasis, in which RirA senses iron via the incorporation of a fragile iron-sulfur cluster that is sensitive to iron and O 2 concentrations. |
