More than 70 different point mutations in human mitochondrial
tRNA genes are correlated with severe disorders, including fatal cardiopathies,
encephalopathies,
myopathies, and others. So far, investigation of the molecular impact(s) of mutations has focused on the affected
tRNA itself by seeking structural and/or functional perturbations capable of interfering with synthesis of the 13 mitochondrion-encoded subunits of respiratory chain complexes. Here, a proteomic approach was used to investigate whether such mutations would affect the pattern of
mitochondrial proteins at a broader level. Analysis of several hundred
mitochondrial proteins from sibling cybrid cell lines by two-dimensional electrophoresis, an approach that takes into account all regulatory steps of mitochondrial and nuclear gene expression, indeed reveals a number of up- and downregulated
proteins when healthy and single-point-mutation-carrying mitochondria representative of either
MELAS or
MERRF syndrome were compared. Assignment by mass spectrometry of the two
proteins which exhibit obvious large quantitative decreases in the levels of both pathologic mitochondria identified nuclear-encoded subunits of
cytochrome c oxidase, a respiratory chain complex. This clearly shows a linkage between the effects of mutations in mitochondrial
tRNA genes and the steady-state level of nuclear-encoded
proteins in mitochondria. It opens new routes toward a large-scale exploration of potential proteic partners involved in the genotype-phenotype correlation of
mitochondrial disorders.