User:Adam Meade/Sandbox 1

Iron Response Regulator (Irr)

---

Background Information

Iron is potentially toxic to cells, as in the presence of oxygen, Fenton reactions can produce reactive oxygen species that can destroy essential biomolecules. Balancing the amount of iron in the cell is important and this importance is apparent from the elaborate mechanisms cells devote to iron homeostasis. Part of this iron balancing is achieved by regulation of iron import. The genes required for ferric citrate transport in Rhodobacter sphaeroides form a cluster in the order fecI-fecR-fecABCDE, encoding a specialized sigma factor and a putative anti-sigma factor that together are responsible for regulated transcription of the ferric citrate transport operon, encoding an ABC-type ferric citrate transporter. In Escherichia coli, fecI transcription is regulated by Fur in response to iron availability; in R. sphaeroides, which lacks Fur, fecI transcription is thought to be regulated by another iron-responsive DNA binding protein, Irr, or the iron response regulator protein.

Irr and Other Iron-Regulating Proteins

Since there are bacteria that have to have iron level-mediating proteins present but do not have the Fur (ferric uptake regulator) protein, there must be another protein that takes its place. In the case of B. japonicum, which does not have the Fur protein, the Irr protein was found to be the regulator of iron levels within the cell.

ReferencesReferences

1) Hamza I, S. Chauhan, R. Hassett, MR O'Brian, 1998. The bacterial irr protein is required for coordination of heme biosynthesis with iron availability.. Journal of Biological Chemistry 34:21669-74.

2) Small, S. K., S. Puri, and M. R. O’Brian. 2009. Heme-dependent metalloregulation by the iron response regulator (Irr) protein in Rhizobium and other alpha-proteobacteria. Biometals 22:89-97.