Metabolites, cofactors and nucleotides cross the compartmentalized mitochondria organelle by specific transporters located in the highly impermeable mitochondrial inner membrane. The flux of those molecules is catalyzed mainly by a superfamily of nuclear-coded proteins known as Mitochondrial Carrier Family [MCF](1). Mitochondrial carriers [MCs] are highly conserved and widely distributed in all eukaryotes. MCs share a common structure consisting of three tandemly related sequences of about 100 amino acids, each containing two hydrophobic motifs and two membrane spanning domains. Alterations of MCs cause metabolic diseases which are directly related to oxidative phosphorylation defects or due to alterations in functions other than oxidative phosphorylation and, in particular, in intermediary metabolism.
Drosophila genome harbors 46 MCs, which share high identity (25%-86%) with their human counterparts. We have previously found that the function of one of these, Scheggia (Sea), the SLC25A1 citrate carrier ortholog, is also required for global histone acetylation and chromosome integrity thus providing compelling evidence of an unanticipated link between metabolite transport and epigenetic control of genome maintenance (10). We plan to use Drosophila melanogaster as model to analyze the role of DmPiC, the Drosophila ortholog of the human phosphate mitochondrial carrier SLC25A3/PiC, which is involved in the mitochondrial phosphate-carrier deficiency disorder. Our preliminary data indicate that DmPiC regulates ATP synthesis and cell proliferation during Drosophila development.
In this proposal I will exploit the power of Drosophila genetics to functionally characterize DmPiC by examining: (1) its function in intracellular metabolism and cell cycle progression (2) its role in mitochondria homeostasis (3) its interaction with Nbs1 which highlights an unanticipated role of Nbs1 in the regulation of mitochondria.
References are in the last section.
In the last two decades deep knowledges have been acquired on the structure of the Mitochondrial Carrier Family, highlighting the importance of their function in several metabolic processes such as biosynthesis of fatty acids, nucleotides, acetyl-CoA and energy production. Mutations in these genes lead to pathological conditions characterized by defects in key metabolic processes. An example is represented by SCL25A1, the citrate carrier, whose mutations results in altered flux of citrate, a key product of TCA cycle. Human patients carrying these kinds of mutations report D-2- and L-2-hydroxyglutaric aciduria, a condition for which there is a lower expulsion of citrate and isocitrate compared to control patients. SLC25A1 deficiency is generally characterized by a severe neurodevelopmental phenotype, including neonatal encephalopathy, respiratory insufficiency, developmental delay, hypotonia, seizures, and early death. Mutations of SCL25A3 have been observed in human patients as well. In this case the resulting phenotype is a reduced ATP production, even if the underlying mechanism has been not well clarified yet (20)
Previous studies from our lab have demonstrated that the mitochondrial citrate carrier is required for protein acetylation and chromosome integrity in both Drosophila and human cells (8). Collectively, these results indicate that mitochondria-dependent intracellular metabolism is crucial for cell and organism survival and indicate that studies on the SCL25 protein family should be enhanced as they could reveal new insights on the molecular and genetic bases underlying several human metabolic diseases. In line with this view my research proposal that aims to understand an unanticipated role for the mitochondrial phosphate carrier in Drosophila cell division, in the regulation of the nuclear protein Nbs1 could provide additional information on this issue.
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