Functional and structural elucidation of the mitochondrial Fe/S protein network

The proteins that bind Fe/S clusters are fundamental in numerous cellular processes, in all types of organisms, not only for their involvement in electron transport, but also in gene expression regulation, like sensors of environmental or intracellular conditions. Biogenesis of the Fe/S proteins is a complex process requiring a large number of accessory proteins. In this pathway, the [4Fe-4S] cluster formation and delivery remain not defined, but mutations in genes encoding proteins involved in ISC maturation, such as NFU1, BOLA3, ISCA2 and IBA57, have been related to a new group of diseases, the multiple mitochondrial dysfunction syndromes (MMDS). In particular, BOLA3 and NFU1 deficiency causes MMDS types 2 and 3, results in the reduced functionality of the respiratory complexes I and II as well as of lipoic acid-dependent enzymes. Similar clinical and biochemical phenotypes in patients with mutations in the late acting factor protein (NFU1), suggested a functional correlation between the two proteins in the late step of the mitochondrial Fe/S protein maturation, even if detailed biochemical investigations of their molecular role in mitochondria have not been reported yet. It’s known that the protein NFU1 binds a [4Fe-4S] cluster, although is still unknown how it is assembled on it. MMDS5 has recently been described in a clinical case report of patients carrying a mutation in ISCA1, but with no further analysis. In the first year of my PhD studies, I characterized the [4Fe-4S] NFU1 and how the [2Fe-2S] GLRX5/BOLA3 complex cooperates in the cluster transfer process. During this year I have worked on two new projects. The second project is focus on in vitro interaction and cluster transfer between NFU1 and ISCA1/ISCA2 complex. The current prevailing model, largely based on studies in S. cerevisiae, proposes that NFU1 receives a [4Fe-4S] cluster assembled on the ISCAs proteins system and then transfers it to selected apo target proteins with the assistance of BOLA3. Based on this model, the project addresses the possible molecular interactions between the [4Fe-4S] ISCA2 protein or/and the ISCA1/ISCA2 complex with NFU1, all involved in [4Fe-4S] cluster transfer to targets enzymes.