
Evidence of a Reduced and Modified Mitochondrial Protein Import Apparatus in Microsporidian Mitosomes
Author(s) -
Ross F. Waller,
Carole Jabbour,
Nickie C. Chan,
Nemin Celik,
Vladimir A Likić,
Terrence D. Mulhern,
Trevor Lithgow
Publication year - 2009
Publication title -
eukaryotic cell
Language(s) - English
Resource type - Journals
eISSN - 1535-9778
pISSN - 1535-9786
DOI - 10.1128/ec.00313-08
Subject(s) - biology , organelle , mitochondrion , microsporidia , encephalitozoon cuniculi , bacterial outer membrane , gene , microbiology and biotechnology , genetics , saccharomyces cerevisiae , spore , escherichia coli
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 microsporidianEncephalitozoon 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 inSaccharomyces 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.