Evolution of peroxiredoxin 5 mitochondrial targeting in mammals : molecular mechanism and functional consequences

To scavenge reactive oxygen species and reactive nitrogen species, the mitochondrial matrix is equipped with antioxidant enzymes, amongst which peroxiredoxin 5 (PRDX5). Mitochondrial localization of this thiol-specific peroxidase results from the presence of an N-terminal mitochondrial targeting sequence (MTS). Human PRDX5 subcellular distribution is not restricted to mitochondria, as it is also found in the cytosol, the peroxisomes, and in a lesser extent, the nucleus. In human, PRDX5 subcellular targeting is dependent on the use of multiple alternative transcription start sites and two alternative in-frame translation initiation sites, which determine whether or not the region encoding the MTS is translated. This work focuses on the interspecific variability of PRDX5 MTS in mammals. We found that, although mitochondrial PRDX5 is conserved in various vertebrate and invertebrate species, PRDX5 mitochondrial targeting has been lost in domestic pig and extant canids. Genomic sequence analyses revealed that the molecular mechanism underlying the abolition of PRDX5 MTS during canid evolution involves a mutation in the first PRDX5 translation initiation codon as well as the appearance of a STOP codon. Moreover, using domestic pig liver mitochondrial extracts, we show that the loss of mitochondrial PRDX5 correlates with high expressions of PRDX3 and glutathione peroxidase 4, suggesting the existence of compensatory mechanisms. However, our results indicate that higher expression of these other mitochondrial peroxidases is not sufficient to maintain high alkyl hydroperoxide reduction rates in pig liver mitochondrial extracts. Therefore, although PRDX5 appears to be dispensable in some mammalian species, we cannot exclude that the abolition of mitochondrial PRDX5 results in a certain weakness at the cellular level under specific oxidative stress conditions. Finally, the functional consequences of the restoration of mitochondrial PRDX5 in Madin-Darby canine kidney (MDCK) cells were investigated. Unexpectedly, we show ...