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Biochem J. 2014 Apr 1;459(1):71-81. doi: 10.1042/BJ20131273.

Frataxin-bypassing Isu1: characterization of the bypass activity in cells and mitochondria.

Author information

1
*Division of Hematology-Oncology, Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, U.S.A.
2
†Department of Pharmacology and Physiology, New Jersey Medical School, Rutgers University, Newark, NJ 07101, U.S.A.

Abstract

Frataxin is a conserved mitochondrial protein, and deficiency underlies the neurodegenerative disease Friedreich's ataxia. Frataxin interacts with the core machinery for Fe-S cluster assembly in mitochondria. Recently we reported that in frataxin-deleted yeast strains, a spontaneously occurring mutation in one of two genes encoding redundant Isu scaffold proteins, bypassed the mutant phenotypes. In the present study we created strains expressing a single scaffold protein, either Isu1 or the bypass mutant M107I Isu1. Our results show that in the frataxin-deletion strain expressing the bypass mutant Isu1, cell growth, Fe-S cluster protein activities, haem proteins and iron homoeostasis were restored to normal or close to normal. The bypass effects were not mediated by changes in Isu1 expression level. The persulfide-forming activity of the cysteine desulfurase was diminished in the frataxin deletion (∆yfh1 ISU1) and was improved by expression of the bypass Isu1 (∆yfh1 M107I ISU1). The addition of purified bypass M107I Isu1 protein to a ∆yfh1 lysate conferred similar enhancement of cysteine desulfurase as did frataxin, suggesting that this effect contributed to the bypass mechanism. Fe-S cluster-forming activity in isolated mitochondria was stimulated by the bypass Isu1, albeit at a lower rate. The rescuing effects of the bypass Isu1 point to ways that the core defects in Friedreich's ataxia mitochondria can be restored.

PMID:
24433162
PMCID:
PMC4021491
DOI:
10.1042/BJ20131273
[Indexed for MEDLINE]
Free PMC Article

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