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

Authors
  • Waller, Ross F
  • Jabbour, Carole
  • Chan, Nickie C
  • Celik, Nermin
  • Likic, Vladimir A
  • Mulhern, Terrence D
  • Lithgow, Trevor
Type
Published Article
Journal
Eukaryotic Cell
Publisher
American Society for Microbiology
Publication Date
Jan 01, 2009
Volume
8
Issue
1
Pages
19–26
Identifiers
DOI: 10.1128/EC.00313-08
PMID: 19028997
Source
Medline
License
Unknown

Abstract

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.

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