The yeast model suggests the use of short peptides derived from mt LeuRS for the therapy of diseases due to mutations in several mt tRNAs

We have previously established a yeastmodel of mitochondrial (mt) diseases. We showed that defective respiratory phenotypes due to point-mutations inmt tRNALeu(UUR), tRNAIle and tRNAVal could be relieved by overexpression of both cognate and non-cognate nuclearly encodedmt aminoacyl-tRNA synthetases (aaRS) LeuRS, IleRS and ValRS. More recently, we showed that the isolated carboxy-terminal domain (Cterm) of yeast mt LeuRS, and even short peptides derived from the human Cterm, have the same suppressing abilities as the whole enzymes. In this work, we extend these results by investigating the activity of a number of mt aaRS from either class I or II towards a panel ofmt tRNAs. The Ctermof both human and yeast mt LeuRS has the same spectrumof activity as mt aaRS belonging to class I and subclass a,which is the most extensive among the whole enzymes. Yeast Cterm is demonstrated to be endowed with mt targeting activity. Importantly, peptide fragments β30_31 and β32_33, derived fromthe human Cterm, have even higher efficiency as well as wider spectrum of activity, thus opening new avenues for therapeutic intervention. Bind-shifting experiments show that the β30_31 peptide directly interacts with human mt tRNALeu(UUR) and tRNAIle, suggesting that the rescuing activity of isolated peptide fragments is mediated by a chaperone-like mechanism. Wide-range suppression appears to be idiosyncratic of LeuRS and its fragments, since it is not shared by Cterminal regions derived from humanmt IleRS or ValRS,which are expected to have very different structures and interactions with tRNAs

Analyzing the suppression of respiratory defects in the yeast model of human mitochondrial tRNA diseases

The respiratory defects associated with mutations in human mitochondrial tRNA genes can be mimicked in yeast, which is the only organism easily amenable to mitochondrial transformation. This approach has shown that overexpression of several nuclear genes coding for factors involved in mitochondrial protein synthesis can alleviate the respiratory defects both in yeast and in human cells. The present paper analyzes in detail the effects of overexpressed yeast and human mitochondrial translation elongation factors EF-Tu. We studied the suppressing activity versus the function in mt translation of mutated versions of this factor and we obtained indications on the mechanism of suppression. Moreover from a more extended search for suppressor genes we isolated factors which might be active in mitochondrial biogenesis. Results indicate that the multiplicity of mitochondrial factors as well as their high variability of expression levels can account for the variable severity of mitochondrial diseases and might suggest possible therapeutic approaches. (C) 2013 Elsevier B.V. All rights reserved