The Presence of Multiple Cellular Defects Associated with a Novel G50E Iron-Sulfur Cluster Scaffold Protein (ISCU) Mutation Leads to Development of Mitochondrial Myopathy

• Published in: The Journal of biological chemistry Vol. 289; no. 15; pp. 10359 - 10377
• Main Authors: Saha, Prasenjit Prasad, Kumar, S.K.Praveen, Srivastava, Shubhi, Sinha, Devanjan, Pareek, Gautam, D'Silva, Patrick
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 11.04.2014; American Society for Biochemistry and Molecular Biology
• Subjects: Amino Acid Sequence; Cell Respiration; Electron Transport System (ETS); Escherichia coli - metabolism; HeLa Cells; Heterozygote; Hsp70; HSP70 Heat-Shock Proteins - metabolism; Humans; Iron - chemistry; Iron-Sulfur Cluster; Iron-Sulfur Protein; Iron-Sulfur Proteins - genetics; Iron-Sulfur Proteins - metabolism; J-protein; Membrane Potentials; Mitochondrial Diseases; Mitochondrial Myopathies - genetics; Mitochondrial Myopathies - metabolism; Molecular Bases of Disease; Molecular Chaperone; Molecular Sequence Data; Mutagenesis; Mutation, Missense; Myopathy; Oxidation-Reduction; Oxidative Stress; Reactive Oxygen Species (ROS); Reactive Oxygen Species - metabolism; Saccharomyces cerevisiae - metabolism; Sequence Homology, Amino Acid; Sulfur - chemistry; J-protein; Hsp70; Reactive Oxygen Species (ROS); Electron Transport System (ETS); Molecular Chaperone; Iron-Sulfur Cluster; Iron-Sulfur Protein; Mitochondrial Diseases; Myopathy
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M113.526665

Iron-sulfur (Fe-S) clusters are versatile cofactors involved in regulating multiple physiological activities, including energy generation through cellular respiration. Initially, the Fe-S clusters are assembled on a conserved scaffold protein, iron-sulfur cluster scaffold protein (ISCU), in coordination with iron and sulfur donor proteins in human mitochondria. Loss of ISCU function leads to myopathy, characterized by muscle wasting and cardiac hypertrophy. In addition to the homozygous ISCU mutation (g.7044G→C), compound heterozygous patients with severe myopathy have been identified to carry the c.149G→A missense mutation converting the glycine 50 residue to glutamate. However, the physiological defects and molecular mechanism associated with G50E mutation have not been elucidated. In this report, we uncover mechanistic insights concerning how the G50E ISCU mutation in humans leads to the development of severe ISCU myopathy, using a human cell line and yeast as the model systems. The biochemical results highlight that the G50E mutation results in compromised interaction with the sulfur donor NFS1 and the J-protein HSCB, thus impairing the rate of Fe-S cluster synthesis. As a result, electron transport chain complexes show significant reduction in their redox properties, leading to loss of cellular respiration. Furthermore, the G50E mutant mitochondria display enhancement in iron level and reactive oxygen species, thereby causing oxidative stress leading to impairment in the mitochondrial functions. Thus, our findings provide compelling evidence that the respiration defect due to impaired biogenesis of Fe-S clusters in myopathy patients leads to manifestation of complex clinical symptoms. Background: Muscle-specific deficiency of iron-sulfur (Fe-S) cluster scaffold protein (ISCU) leads to myopathy. Results: Cells carrying the myopathy-associated G50E ISCU mutation demonstrate impaired Fe-S cluster biogenesis and mitochondrial dysfunction. Conclusion: Reduced mitochondrial respiration as a result of diminished Fe-S cluster synthesis results in muscle weakness in myopathy patients. Significance: The molecular mechanism behind disease progression should provide invaluable information to combat ISCU myopathy.