Inhibition of Fe-S cluster biosynthesis decreases mitochondrial iron export: Evidence that Yfh1p affects Fe-S cluster synthesis

Abstract

Decreased expression of Yfh1p in the budding yeast, Saccharomyces cerevisiae, and the orthologous human gene frataxin results in respiratory deficiency and mitochondrial iron accumulation. The absence of Yfh1p decreases mitochondrial iron export. We demonstrate that decreased expression of Nfs1p, the yeast cysteine desulfurase that plays a central role in Fe-S cluster synthesis, also results in mitochondrial iron accumulation due to decreased export of mitochondrial iron. In the absence of Yfh1p, activity of Fe-Scontaining enzymes (aconitase, succinate dehydrogenase) is decreased, whereas the activity of a non-Fe-S-containing enzyme (malate dehydrogenase) is unaffected. Aconitase protein was abundant even though the activity of aconitase was decreased in both aerobic and anaerobic conditions. These results demonstrate a direct role of Yfh1p in the formation of Fe-S clusters and indicate that mitochondrial iron export requires Fe-S cluster biosynthesis.F rataxin is a highly conserved protein found in all eukaryotes.The protein is encoded by a nuclear gene and is localized in the mitochondrial matrix. Deficits in frataxin protein result in Friedreich ataxia, a neurologic and cardiac disorder (1). Deletion of Yfh1p, the frataxin orthologue in yeast, leads to a respiratory defect resulting from excessive mitochondrial iron accumulation, which increases oxidant damage (2). The increase in mitochondrial iron is caused by malregulation of the mitochondrial iron cycle (3). Mitochondrial iron accumulation is only seen when cytosolic iron levels are high. Reduction in cytosolic iron due to either low-iron media (3, 4), deletion of genes required for high-affinity iron transport (3), or increased vacuolar iron transport (5), prevents excessive mitochondrial iron accumulation and will preserve respiratory activity in ⌬yfh1 cells.In yeast, the proteins involved in Fe-S cluster synthesis are compartmentalized in the mitochondria where Fe-S clusters are synthesized for use both in mitochondria and for export to cytosolic proteins (6). Excessive mitochondrial iron is also seen as a result of deletion of genes required for synthesis of Fe-S clusters (for review, see ref. 6). For example, decreased expression of Nfs1p, the cysteine desulfurase (7, 8), Isu1p, a putative scaffolding protein (9), Yah1p, a putative ferredoxin (10), and Arh1p, a putative ferredoxin reductase (11), results in mitochondrial iron accumulation. In addition, reduced expression of Atm1p, a putative mitochondrial Fe-S exporter, also leads to accumulation of toxic levels of mitochondrial iron (7). The mechanism by which iron accumulates has not been elucidated. Herein, we describe that reduced expression of a critical enzyme involved in Fe-S synthesis, Nfs1p, results in mitochondrial iron accumulation through decreased mitochondrial iron export, similar to that seen in ⌬yfh1 cells (3). This result indicates that mitochondrial iron export depends on Fe-S cluster synthesis, suggesting that Yfh1p may play a role in Fe-S cluster synthesis. To test this hypothesis...

The MCK mouse heart model of Friedreich's ataxia: Alterations in iron-regulated proteins and cardiac hypertrophy are limited by iron chelation

“…Previous data in combination with the current study indicate that a major control of Fe uptake is MIT Fe utilization for functions such as ISC synthesis, which is depressed in the absence of Fxn (22). The mechanism of communication between the mitochondrion and cytosol that alters Fe trafficking to ''satisfy'' the MIT demand remains unknown.…”

Yeast Contain a Non-proteinaceous Pool of Copper in the Mitochondrial Matrix

“…The increase in the mitochondrial labile iron pool has deleterious consequences. The elevation in labile iron in mitochondria of cells depleted for Yfh1 or Isa1 results in an increase in petite formation (59,60). Whereas increases in the labile iron pool in mitochondria are deleterious, a 5-10-fold increase in the matrix copper pool is not associated with mitochondrial DNA damage.…”

Metal Ion availability in mitochondria

“…Although the identity of the ligand remains unresolved, the matrix CuL pool is accessible to a heterologous cuproenzyme (Cobine et al 2004). The mechanism by which Aft1 (and Aft2) sense cellular iron levels involves the mitochondrion (Chen et al 2004;Chen et al 2002). Cells defective for Fe-S cluster biogenesis within the mitochondrial matrix exhibit constitutive expression of the iron regulon genes (Chen et al 2002).…”

“…The mechanism by which Aft1 (and Aft2) sense cellular iron levels involves the mitochondrion (Chen et al 2004;Chen et al 2002). Cells defective for Fe-S cluster biogenesis within the mitochondrial matrix exhibit constitutive expression of the iron regulon genes (Chen et al 2002). The constitutive activity of Aft1 is due to an impairment of a signal arising from the mitochondrial Fe-S biosynthetic machinery and not due to Fe-deficiency within the cytoplasm (Chen et al 2004).…”