Human Molecular Genetics Advance Access published online on April 21, 2006
Human Molecular Genetics, doi:10.1093/hmg/ddl106
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1 Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada H3A 2B4
* To whom correspondence should be addressed. Defects in mitochondrial translation are associated with a remarkable, but unexplained, diversity of clinical phenotypes. Here we have investigated the molecular basis for tissue specificity in patients with a fatal hepatopathy due to mutations in the mitochondrial translation elongation factor EFG1. Blue-native gel electrophoresis revealed unique, tissue-specific patterns in the nature and severity of the defect. Liver was the most severely affected tissue, with less than 10% residual assembly of complexes I and IV, and a 50% decrease in complex V. Skeletal muscle showed a 50% reduction in complex I, and complexes IV and V were 20% of control. In fibroblasts, complexes I and IV were 20% of control, and there was a 40-60 % reduction in complexes III and V. In contrast, except for a 50% decrease in complex IV, all complexes were near normal in heart. The severity of the defect paralleled the steady-state level of the mutant EFG1 protein, which varied from 60% of control in heart to undetectable in liver. The ratio of translation elongation factors EFTu:EFTs increased from 1:6 to 1:2 in patient heart, whereas in liver it decreased from 1:1 to 1:4. Over-expression of either EFTu or EFTs in control and patient fibroblasts produced dominant negative effects, indicating that the relative abundance of these factors is an important determinant of translation efficiency. Our results demonstrate marked differences among tissues in the organization of the mitochondrial translation system and its response to dysfunction, and explain the severe hepatopathy, but normal cardiac function in EFG1 patients.
Received March 20, 2006
Revised April 13, 2006
Accepted April 13, 2006
Article
The molecular basis for tissue specificity of the oxidative phosphorylation deficiencies in patients with mutations in the mitochondrial translation factor EFG1
Hana Antonicka 1,
Florin Sasarman 1,
Nancy G. Kennaway 2,
and
Eric A. Shoubridge 3 *
2 Department of Molecular and Medical Genetics, Oregon Health & Science University, Portland, Oregon 97239, USA
3 Montreal Neurological Institute, McGill University, 3801 University Street, Montreal, Quebec H3A 2B4, Canada.; Department of Human Genetics, Oregon Health & Science University, Portland, Oregon 97239, USA
Eric A. Shoubridge, E-mail: eric{at}ericpc.mni.mcgill.ca
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