Frataxin, a molecule of mystery: trading stability for function in its iron-binding site.

What are the structural implications for iron binding by frataxin, the mitochondrial protein whose decreased expression results in Friedreich's ataxia? Though frataxin has been shown to be essential for proper handling of iron within mitochondria (e.g. for iron-sulfur cluster and haem biosynthesis), its exact molecular function remains unclear. In this issue of the Biochemical Journal, Correia and colleagues. investigate the relationship between structure and function at the putative iron-binding site of Yfh1 (yeast frataxin). Using a host of Yfh1 combination point mutants, the authors observe that the presence of a semi-conserved pocket of negative charge within the 'acidic ridge' region (thought to be responsible for iron binding) only mildly enhances Yfh1's ability to bind iron, though it does significantly increase the protein's structural flexibility. The general emerging view is that frataxin's keystone role in mitochondrial iron metabolism depends on iron binding. This appears to have downstream effects on protein-protein interactions that are crucial for frataxin function. The current results reveal a somewhat delicate relationship between iron binding and structural plasticity that may help unravel the enigma of frataxin's metabolic roles.