Understanding the function of frataxin in eukaryotes

The neurodegenerative disease Friedreich ataxia is caused by reduced expression levels of Frataxin, an essential protein highly conserved from bacteria to humans. More than 15 years of studies have not been sufficient to unambiguously identify the cellular function of frataxin, although increasing evidence links this protein to iron-sulfur cluster biogenesis. Both in prokaryotes and in eukaryotes frataxin has been shown to interact with the desulfurase IscS/Nfs1 and the scaffold protein IscU/Isu. These are the components central to the cluster assembly machinery, the first being the enzyme that produces highly reactive persulfide groups, the second being the scaffold on which the clusters are formed. However, while in prokaryotes frataxin has been shown to act as an inhibitor of enzymatic cluster formation, in eukaryotes it seems to activate the same process although a number of considerations make the latter results unreliable. Further studies are needed to resolve the discrepancy.

This PhD project will aim at characterizing the interaction between frataxin, Nfs1 and Isu and establish its role using in parallel the S. cerevisiae and human proteins. The student will have to produce the three proteins in isolation and/or co-expression, ascertain that they are correctly folded and quantify their interactions. The effect of frataxin binding on the kinetics of enzymatic cluster formation will then be tested using an assay already developed in our group. The project will require the use of different techniques such as isothermal calorimetry, Plasmon resonance techniques, NMR and fluorescence methods. Attempts in crystallizing the complexes will also be made. Because of the necessity to use very different biochemical and biophysical techniques the project provides ample opportunities of training.

The work should lead both to a better understanding of the mechanisms of iron-sulfur cluster formation and to the establishment of the frataxin function.