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Evidence of a reduced and modified mitochondrial protein import apparatus in microsporidian mitosomes

Ross F Waller1, Carole Jabbour, Nickie C Chan

  • 1School of Botany, University of Melbourne, Victoria, Australia. r.waller@unimelb.edu.au

Eukaryotic Cell
|November 26, 2008
PubMed

Insights

Microsporidia have highly reduced mitochondria with a simplified protein import system. Researchers found a shortened Tom70 protein in Encephalitozoon cuniculi, indicating significant evolutionary adaptation.

Area of Science:

  • Mycology
  • Parasitology
  • Cell Biology

Background:

  • Microsporidia are obligate intracellular parasites closely related to fungi.
  • Parasitism has driven extreme genomic, biochemical, and cellular reductions in microsporidia.
  • Mitochondria in microsporidia are severely reduced, lacking typical functions like ATP synthesis.

Purpose of the Study:

  • To investigate the mitochondrial protein import apparatus in the microsporidian Encephalitozoon cuniculi.
  • To characterize the function of a reduced outer membrane receptor, Tom70, in microsporidian mitochondria.

Main Methods:

  • Genomic data analysis using hidden Markov models to identify import machinery proteins.
  • Expression of the Encephalitozoon cuniculi Tom70 (EcTom70) in Saccharomyces cerevisiae.
  • Analysis of EcTom70 topology and function in yeast mitochondria.

Main Results:

  • Evidence of a reduced and modified mitochondrial protein import machinery in Encephalitozoon cuniculi.
  • A putative outer membrane receptor, Tom70, is shortened but retains conserved structural features (tetratricopeptide repeats).
  • EcTom70 correctly inserts into yeast mitochondria but cannot rescue growth defects in Tom70-deficient yeast, suggesting functional limitations.

Conclusions:

  • The mitochondrial protein import system in microsporidia is significantly reduced and modified, consistent with their parasitic lifestyle.
  • The functional capacity of microsporidian mitochondria, including protein import, is severely compromised.
  • Further genomic scanning revealed a broader reduction in the mitochondrial import machinery system.

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