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Eukaryotic Cell, January 2009, p. 19-26, Vol. 8, No. 1
1535-9778/09/$08.00+0     doi:10.1128/EC.00313-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Evidence of a Reduced and Modified Mitochondrial Protein Import Apparatus in Microsporidian Mitosomes{triangledown}

Ross F. Waller,1* Carole Jabbour,1,2 Nickie C. Chan,2 Nermin Celik,2 Vladimir A. Likic,2 Terrence D. Mulhern,2 and Trevor Lithgow2,{dagger}

School of Botany, University of Melbourne, Victoria 3010, Australia,1 Department of Biochemistry and Molecular Biology, Bio21 Institute of Biotechnology and Molecular Science, University of Melbourne, Victoria 3010, Australia2

Received 15 September 2008/ Accepted 8 November 2008

Microsporidia are a group of highly adapted obligate intracellular parasites that are now recognized as close relatives of fungi. Their adaptation to parasitism has resulted in broad and severe reduction at (i) a genomic level by extensive gene loss, gene compaction, and gene shortening; (ii) a biochemical level with the loss of much basic metabolism; and (iii) a cellular level, resulting in lost or cryptic organelles. Consistent with this trend, the mitochondrion is severely reduced, lacking ATP synthesis and other typical functions and apparently containing only a fraction of the proteins of canonical mitochondria. We have investigated the mitochondrial protein import apparatus of this reduced organelle in the microsporidian Encephalitozoon cuniculi and find evidence of reduced and modified machinery. Notably, a putative outer membrane receptor, Tom70, is reduced in length but maintains a conserved structure chiefly consisting of tetratricopeptide repeats. When expressed in Saccharomyces cerevisiae, EcTom70 inserts with the correct topology into the outer membrane of mitochondria but is unable to complement the growth defects of Tom70-deficient yeast. We have scanned genomic data using hidden Markov models for other homologues of import machinery proteins and find evidence of severe reduction of this system.

* Corresponding author. Mailing address: School of Botany, University of Melbourne, Victoria 3010, Australia. Phone: 61 3 8344 5042. Fax: 61 3 9347 5460. E-mail: r.waller{at}unimelb.edu.au

{triangledown} Published ahead of print on 21 November 2008.

{dagger} Present address: Department of Biochemistry & Molecular Biology, Monash University, Victoria 3800, Australia.

Eukaryotic Cell, January 2009, p. 19-26, Vol. 8, No. 1
1535-9778/09/$08.00+0     doi:10.1128/EC.00313-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Hjort, K., Goldberg, A. V., Tsaousis, A. D., Hirt, R. P., Embley, T. M. (2010). Diversity and reductive evolution of mitochondria among microbial eukaryotes. Phil Trans R Soc B 365: 713-727 [Abstract] [Full Text]  
  • Lithgow, T., Schneider, A. (2010). Evolution of macromolecular import pathways in mitochondria, hydrogenosomes and mitosomes. Phil Trans R Soc B 365: 799-817 [Abstract] [Full Text]  
  • Clements, A., Bursac, D., Gatsos, X., Perry, A. J., Civciristov, S., Celik, N., Likic, V. A., Poggio, S., Jacobs-Wagner, C., Strugnell, R. A., Lithgow, T. (2009). The reducible complexity of a mitochondrial molecular machine. Proc. Natl. Acad. Sci. USA 106: 15791-15795 [Abstract] [Full Text]  
  • Dagley, M. J., Dolezal, P., Likic, V. A., Smid, O., Purcell, A. W., Buchanan, S. K., Tachezy, J., Lithgow, T. (2009). The Protein Import Channel in the Outer Mitosomal Membrane of Giardia intestinalis. Mol Biol Evol 26: 1941-1947 [Abstract] [Full Text]  


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