Triplet-pore structure of a highly divergent TOM complex of hydrogenosomes in Trichomonas vaginalis

• Published in: PLoS biology 2019-01, Vol.17 (1), p.e3000098-e3000098
• Main Authors: Makki, Abhijith, Rada, Petr, Žárský, Vojtěch, Kereïche, Sami, Kováčik, Lubomír, Novotný, Marian, Jores, Tobias, Rapaport, Doron, Tachezy, Jan
• Format: Article
• Language: English
• Subjects: Acids; Assembly; Biochemistry; Bioinformatics; Biology; Biology and Life Sciences; Carrier Proteins - genetics; Carrier Proteins - metabolism; Carrier Proteins - physiology; Channel pores; Electron microscopy; Endosymbionts; Genetic aspects; Heat shock proteins; Homology; Hydrogenosomes; Imports; Membrane proteins; Membrane Proteins - metabolism; Membrane Transport Proteins - metabolism; Mitochondria; Mitochondria - metabolism; Mitochondrial Membrane Transport Proteins - metabolism; Molecular weight; Organelles; Parasitic diseases; Parasitology; Phylogeny; Physical sciences; Porosity; Protein transport; Protein Transport - physiology; Proteins; Receptor mechanisms; Receptors; Research and Analysis Methods; Sexually transmitted diseases; Software; STD; Substrates; Translocase; Translocation; Trichomonas vaginalis; Trichomonas vaginalis - metabolism; Trichomonas vaginalis - pathogenicity; Trichomonas vaginalis - physiology
• ISSN: 1545-7885; 1544-9173; 1545-7885
• DOI: 10.1371/journal.pbio.3000098

Mitochondria originated from proteobacterial endosymbionts, and their transition to organelles was tightly linked to establishment of the protein import pathways. The initial import of most proteins is mediated by the translocase of the outer membrane (TOM). Although TOM is common to all forms of mitochondria, an unexpected diversity of subunits between eukaryotic lineages has been predicted. However, experimental knowledge is limited to a few organisms, and so far, it remains unsettled whether the triplet-pore or the twin-pore structure is the generic form of TOM complex. Here, we analysed the TOM complex in hydrogenosomes, a metabolically specialised anaerobic form of mitochondria found in the excavate Trichomonas vaginalis. We demonstrate that the highly divergent β-barrel T. vaginalis TOM (TvTom)40-2 forms a translocation channel to conduct hydrogenosomal protein import. TvTom40-2 is present in high molecular weight complexes, and their analysis revealed the presence of four tail-anchored (TA) proteins. Two of them, Tom36 and Tom46, with heat shock protein (Hsp)20 and tetratricopeptide repeat (TPR) domains, can bind hydrogenosomal preproteins and most likely function as receptors. A third subunit, Tom22-like protein, has a short cis domain and a conserved Tom22 transmembrane segment but lacks a trans domain. The fourth protein, hydrogenosomal outer membrane protein 19 (Homp19) has no known homology. Furthermore, our data indicate that TvTOM is associated with sorting and assembly machinery (Sam)50 that is involved in β-barrel assembly. Visualisation of TvTOM by electron microscopy revealed that it forms three pores and has an unconventional skull-like shape. Although TvTOM seems to lack Tom7, our phylogenetic profiling predicted Tom7 in free-living excavates. Collectively, our results suggest that the triplet-pore TOM complex, composed of three conserved subunits, was present in the last common eukaryotic ancestor (LECA), while receptors responsible for substrate binding evolved independently in different eukaryotic lineages.