Iron is a fundamental requirement for virtually all cells, but it also potentially toxic if it is present in incorrect concentrations or locations. Thus, it is essential that cellular concentrations are carefully regulated. Iron-sulfur clusters are cofactors in many proteins and carry out a wide range of functions, including electron transfer and catalysis. They are also common found as cofactors in transcriptional regulators that coordinate the cellular response to changing conditions, including in response to iron levels.

In mammals, iron regulatory protein 1 (IRP1) interacts with mRNA to promote or inhibit the translation of proteins involved in iron metabolism (eg transferrin receptor and ferritin).  Low cellular iron leads to the loss of the cluster of IRP1, facilitating interaction of the cluster-free (apo-) protein with mRNA which results in increased iron import.  The mechanism of cluster disassembly in IRP1 is unclear.  In many bacteria, Fur plays a central role in iron regulation. However, in alpha-proteobacteria, which includes some of the most widespread and abundant of all bacteria, iron metabolism is regulated very differently. A key part of this regulatory network is the global iron regulator RirA, which binds an iron-sulfur cluster.  However, the precise nature of the cluster and the mechanism by which it senses iron is not known.

In general, progress in understanding the biochemical and molecular details of the functions of iron-sulfur cluser proteins, and particularly those involved in regulation, has been hampered by the difficulties of working with these O2-sensitive proteins. This project aims to address, using a range of biophysical chemistry approaches, fundamental aspects of iron-sensing mechanisms in mammals and bacteria and thus to uncover the mechanistic detail that underpin their modes of regulation.  The project will be carried out within the UEA Centre for Molecular and Structural Biochemistry (CMSB) and will have access to the world-renowned spectroscopic and analytical facilities available at UEA.  The project will also benefit from the recently installed ESI-TOF mass spectrometry facility in the School which is aimed towards the development of metal-protein interactions by mass spectrometry.

Zhang, B., Crack, J. C., Subramanian, S., Green, J., Thomson, A. J., Le Brun, N. E. and Johnson, M. K. (2012) Reversible cycling between partially cysteine persulfide-ligated [2Fe-2S] clusters and cysteine ligated [4Fe-4S] clusters in FNR. Proc. Nat. Acad. Sci. USA. 109, 15734-15739

Crack, J. C., Green, J., Thomson, A. J. and Le Brun, N. E. (2012) Iron-sulfur sensor-regulators.  Curr. Opin. Chem. Biol. 16, 35-44

Crack, J. C., Smith, L. J., Stapleton, M. R., Peck, J., Watmough, N. J., Buttner, M. J., Buxton, R. S., Green, J., Oganesyan, V. S., Thomson, A. J., and Le Brun, N. E. (2011) Mechanistic insight into the nitrosylation of the [4Fe-4S] cluster of WhiB-like proteins. J. Am. Chem. Soc. 133, 1112-1121

Singleton, C., White, G. F., Todd, J. D., Marritt, S. J., Cheesman, M. R., Johnston, A. W. B. and Le Brun, N. E. (2010) Heme-responsive DNA binding by the global iron regulator Irr from Rhizobium leguminosarum J. Biol. Chem., 285, 16023-16031

Todd, J. D., Wexler, M., Sawers, G., Yeoman, K. H., Poole, P. S. and Johnston, A. W. (2002). RirA, an iron-responsive regulator in the symbiotic bacterium Rhizobium leguminosarum. Microbiology  148:4059-71