BACKGROUND: The Tim17 family of proteins plays a fundamental role in the biogenesis of mitochondria. Three Tim17 family proteins, Tim17, Tim22, and Tim23, are the central components of the widely conserved multi-subunit protein translocases, TIM23 and TIM22, which mediate protein transport across and into the inner mitochondrial membrane, respectively. In addition, several Tim17 family proteins occupy the inner and outer membranes of plastids. RESULTS: We have performed comprehensive sequence analyses on 5631 proteomes from all domains of life deposited in the Uniprot database. The analyses showed that the Tim17 family of proteins is much more diverse than previously thought and involves at least ten functionally and phylogenetically distinct groups of proteins. As previously shown, mitochondrial inner membrane accommodates prototypical Tim17, Tim22 and Tim23 and two Tim17 proteins, TIMMDC1 and NDUFA11, which participate in the assembly of complex I of the respiratory chain. In addition, we have identified Romo1/Mgr2 as Tim17 family member. The protein has been shown to control lateral release of substrates fromTIM23 complex in yeast and to participate in the production of reactive oxygen species in mammalian cells. Two peroxisomal proteins, Pmp24 and Tmem135, of so far unknown function also belong to Tim17 protein family. Additionally, a new group of Tim17 family proteins carrying a C-terminal coiled-coil domain has been identified predominantly in fungi. CONCLUSIONS: We have mapped the distribution of Tim17 family members in the eukaryotic supergroups and found that the mitochondrial Tim17, Tim22 and Tim23 proteins, as well as the peroxisomal Tim17 family proteins, were all likely to be present in the last eukaryotic common ancestor (LECA). Thus, kinetoplastid mitochondria previously identified as carrying a single Tim17protein family homologue are likely to be the outcome of a secondary reduction. The eukaryotic cell has modified mitochondrial Tim17 family proteins to mediate different functions in multiple cellular compartments including mitochondria, plastids and peroxisomes. Concerning the origin of Tim17 protein family, our analyses do not support the affiliation of the protein family and the component of bacterial amino acid permease. Thus, it is likely that Tim17 protein family is exclusive to eukaryotes. REVIEWERS: The article was reviewed by Michael Gray, Martijn Huynen and Kira Makarova.
BACKGROUND: Peroxisomes are ubiquitous eukaryotic organelles that compartmentalize a variety of metabolic pathways that are primarily related to the oxidative metabolism of lipids and the detoxification of reactive oxygen species. The importance of peroxisomes is underscored by serious human diseases, which are caused by disorders in peroxisomal functions. Some eukaryotic lineages, however, lost peroxisomes. These organisms are mainly anaerobic protists and some parasitic lineages including Plasmodium and parasitic platyhelminths. Here we performed a systematic in-silico analysis of peroxisomal markers among metazoans to assess presence of peroxisomes and peroxisomal enzymes. RESULTS: Our analyses reveal an obvious loss of peroxisomes in all tested flukes, tapeworms, and parasitic roundworms of the order Trichocephalida. Intriguingly, peroxisomal markers are absent from the genome of the free-living tunicate Oikopleura dioica, which inhabits oxygen-containing niches of sea waters. We further map the presence and predicted subcellular localization of putative peroxisomal enzymes, showing that in organisms without the peroxisomal markers the set of these enzymes is highly reduced and none of them contains a predicted peroxisomal targeting signal. CONCLUSIONS: We have shown that several lineages of metazoans independently lost peroxisomes and that the loss of peroxisomes was not exclusively associated with adaptation to anaerobic habitats and a parasitic lifestyle. Although the reason for the loss of peroxisomes from O. dioica is unclear, organisms lacking peroxisomes, including the free-living O. dioica, share certain typical r-selected traits: high fecundity, limited ontogenesis and relatively low complexity of the gene content. We hypothesize that peroxisomes are generally the first compartment to be lost during evolutionary reductions of the eukaryotic cell.
- MeSH
- bezobratlí genetika MeSH
- biologická evoluce * MeSH
- fylogeneze MeSH
- genom * MeSH
- obratlovci genetika MeSH
- paraziti genetika MeSH
- peroxizomy genetika MeSH
- sekvenční analýza DNA MeSH
- Urochordata genetika MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
