A trypanosomal orthologue of an intermembrane space chaperone has a non-canonical function in biogenesis of the single mitochondrial inner membrane protein translocase

PLoS Pathog. 2017 Aug 21;13(8):e1006550. doi: 10.1371/journal.ppat.1006550. eCollection 2017 Aug.


Mitochondrial protein import is essential for Trypanosoma brucei across its life cycle and mediated by membrane-embedded heterooligomeric protein complexes, which mainly consist of trypanosomatid-specific subunits. However, trypanosomes contain orthologues of small Tim chaperones that escort hydrophobic proteins across the intermembrane space. Here we have experimentally analyzed three novel trypanosomal small Tim proteins, one of which contains only an incomplete Cx3C motif. RNAi-mediated ablation of TbERV1 shows that their import, as in other organisms, depends on the MIA pathway. Submitochondrial fractionation combined with immunoprecipitation and BN-PAGE reveals two pools of small Tim proteins: a soluble fraction forming 70 kDa complexes, consistent with hexamers and a second fraction that is tightly associated with the single trypanosomal TIM complex. RNAi-mediated ablation of the three proteins leads to a growth arrest and inhibits the formation of the TIM complex. In line with these findings, the changes in the mitochondrial proteome induced by ablation of one small Tim phenocopy the effects observed after ablation of TbTim17. Thus, the trypanosomal small Tims play an unexpected and essential role in the biogenesis of the single TIM complex, which for one of them is not linked to import of TbTim17.

MeSH terms

  • Blotting, Northern
  • Chromatography, High Pressure Liquid
  • Immunoprecipitation
  • Life Cycle Stages
  • Mass Spectrometry
  • Membrane Transport Proteins / metabolism*
  • Microscopy, Fluorescence
  • Mitochondrial Membrane Transport Proteins / metabolism*
  • Mitochondrial Membranes / metabolism
  • Molecular Chaperones / metabolism*
  • Protein Transport / physiology*
  • Trypanosoma brucei brucei / growth & development*
  • Trypanosoma brucei brucei / metabolism


  • Membrane Transport Proteins
  • Mitochondrial Membrane Transport Proteins
  • Molecular Chaperones

Grants and funding

AH gratefully acknowledges a fellowship from the Peter und Traudl Engelhorn foundation (http://ptes.2c4b.de/). Research in the group of BW was funded by the Deutsche Forschungsgemeinschaft and the Excellence Initiative of the German Federal & State Governments (EXC 294 BIOSS Centre for Biological Signalling Studies; http://www.dfg.de/en/research_funding/programmes/list/projectdetails/index.jsp?id=39236281). Research in the lab of AS was supported by grant 138355 (http://p3.snf.ch/Project-138355) and in part by the NCCR "RNA & Disease" (http://www.snf.ch/en/researchinFocus/nccr/rna-disease/Pages/default.aspx) both funded by the Swiss National Science Foundation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.