An amino acid substitution in the pyruvate dehydrogenase E1α gene, affecting mitochondrial import of the precursor protein

F. Takakubo, P. Cartwright, N. Hoogenraad, D. R. Thorburn, F. Collins, T. Lithgow, H. H.M. Dahl

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Abstract

A mutation in the mitochondrial targeting sequence was characterized in a male patient with X chromosome-linked pyruvate dehydrogenase E1α deficiency. The mutation was a base substitution of G by C at nucleotide 134 in the mitochondrial targeting sequence of the PDHA1 gene, resulting in an arginine- to-proline substitution at codon 10 (R10P). Pyruvate dehydrogenase activity in cultured skin fibroblasts was 28% of the control value, and immunoblot analysis revealed a decreased level of pyruvate dehydrogenase E1α immunoreactivity. Chimeric constructs in which the normal and mutant pyruvate dehydrogenase E1α targeting sequences were attached to the mitochondrial matrix protein ornithine transcarbamylase were synthesized in a cell free translation system, and mitochondrial import of normal and mutant proteins was compared in vitro. The results show that ornithine transcarbamylase targeted by the mutant pyruvate dehydrogenase E1α sequence was translocated into the mitochondrial matrix at a reduced rate, suggesting that defective import is responsible for the reduced pyruvate dehydrogenase level in mitochondria. The mutation was also present in an affected brother and the mildly affected mother. The clinical presentations of this X chromosome- linked disorder in affected family members are discussed. To our knowledge, this is the first report of an amino acid substitution in a mitochondrial targeting sequence resulting in a human genetic disease.

Original languageEnglish
Pages (from-to)772-780
Number of pages9
JournalAmerican Journal of Human Genetics
Volume57
Issue number4
Publication statusPublished - 1 Jan 1995
Externally publishedYes

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