Biogenesis of iron-sulfur clusters and intracellular iron metabolism

Iron-sulfur ([Fe-S]) clusters represent one of natures most diverse and ubiquitous protein prosthetic groups. [Fe-S] proteins are integral for diverse biological processes. Reconstitution of apo-proteins can occur by exogenously adding excess iron and sulfide. However, due to the toxicity of iron and sulfide, it is most likely that proteins coordinate [Fe-S] cluster assembly in cells. The first part of this dissertation addressed the iron donor for [Fe-S] cluster assembly. Recently, it has been shown that IscA is capable of binding iron with an association constant of 3.0 x 10¹⁹M^-1. In addition, iron-loaded IscA is capable of donating iron to the proposed scaffold IscU for nascent [Fe-S] cluster assembly. We show that hIscA, the human homolog of <i>E. coli</i> IscA, functions as an iron chaperone for the assembly of [Fe-S] clusters in <i>E. coli</i> IscU. hIscA’s iron binding ability is similar to <i>E. coli</i> IscA. Moreover, hIscA is able to donate iron to IscU in the presence of 100-fold excess citrate, a metabolite capable of binding iron. This comparison signifies that [Fe-S] cluster assembly is conserved from bacteria to humans. The second part of this dissertation determined the participation of Ferritin A (FtnA) in [Fe-S] cluster assembly. FtnA, the major iron storage protein in <i>E. coli</i>, could serve as an iron reservoir when intracellular iron is depleted. We have shown that FtnA is capable of buffering iron when oxidative stress disrupts nascent [Fe-S] clusters and alleviates the production of hydroxyl radicals. Moreover, when physiological conditions return, IscA is able to retrieve iron from FtnA for [Fe-S] cluster assembly. The final part of this dissertation corroborated the interrelatedness of the oxidative and nitrosative stress response pathways. NsrR, a nitric oxide (NO) sensitive transcriptional repressor, is shown to coordinate a redox active [2Fe-2S] cluster with a midpoint redox potential of -346 ± 7 mV. The NsrR [2Fe-2S] cluster reacts with NO more quickly than other [Fe-S] proteins, signifying its role as a NO sensor. Finally, modification of the NsrR [2Fe-2S] cluster by NO results in the formation of a protein-bound dinitrosyl iron complex, relieving its DNA binding ability as a repressor.

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Grantor

Biological Sciences

Year dc:date.available

2009

Author dc:creator

• Bitoun, Jacob Philip

• operon
• Bacterioferritin
• DNIC
• EPR
• transcription
• reduction
• oxidation

Statement dc:rights

• unrestricted
• Release the entire work immediately for access worldwide.

Identifier

etd-07092009-144958
https://repository.lsu.edu/gradschool_dissertations/670

OAI identifier oai:identifier

oai:repository.lsu.edu:gradschool_dissertations-1669