The mitosome, a novel organelle related to mitochondria in the amitochondrial parasite Entamoeba histolytica

Abstract

Ultrastructural analysis of Entamoeba histolytica reveals that this intestinal human pathogen lacks recognizable mitochondria, but the presence in its genome of genes encoding proteins of mitochondrial origin suggests the existence of a mitochondrially derived compartment. We have cloned the full‐length E. histolytica gene encoding one such protein, chaperonin CPN60, and have characterized its structure and expression. Using an affinity‐purified antibody raised against recombinant protein, we have localized native E. histolytica CPN60 to a previously undescribed organelle of putative mitochondrial origin, the mitosome. Most cells contain only one mitosome, as determined by immunofluorescence studies. Entamoeba histolytica CPN60 has an amino‐terminal extension reminiscent of known mitochondrial and hydrogenosomal targeting signals. Deletion of the first 15 amino acids of CPN60 leads to an accumulation of the truncated protein in the cytoplasm. However, this mutant phenotype can be reversed by replacement of the deleted amino acids with a mitochondrial targeting signal from Trypanosoma cruzi HSP70. The observed functional conservation between mitochondrial import in trypanosomes and mitosome import in Entamoeba is strong evidence that the E. histolytica organelle housing chaperonin CPN60 represents a mitochondrial remnant.

Multiple secondary origins of the anaerobic lifestyle in eukaryotes

“…These organelles are called hydrogenosomes (Mü ller 1993;, remnant mitochondria (Williams et al 2002) or mitosomes (Tovar et al 1999(Tovar et al , 2003, with the latter two terms sometimes used interchangeably for the same organelle. There are only two double-membraned organelles, mitochondria and primary plastids, of undisputed bacterial origin in eukaryotes.…”

“…There are only two double-membraned organelles, mitochondria and primary plastids, of undisputed bacterial origin in eukaryotes. Thus the simplest, and hence preferable, hypothesis to explain the observations that proteins typically found in mitochondria are present in doublemembrane-bounded Archezoan organelles is that all such organelles share common ancestry with mitochondria Tovar et al 1999Tovar et al , 2003Williams et al 2002). Mitochondria, mitosomes and hydrogenosomes are evolutionary homologues sensu Owen and Darwin (Owen 1843;Darwin 1859), and the differences between them are the products of descent with modification from a common ancestral organelle.…”

Mitochondrial-type iron–sulfur cluster biosynthesis genes (IscS and IscU) in the apicomplexan Cryptosporidium parvum

“…All of these organelles are thought to be descendents of a common endosymbiont which gave rise to both hydrogenosomes and mitochondria (Martin & Müller, 1998;Dyall & Johnson, 2000;Rotte et al, 2000;Martin et al, 2001). Putative mitochondrial relicts have also been identified in the parasitic amoeba Entamoeba histolytica (mitosome, Tovar et al, 1999;crypton, Mai et al, 1999) and the microsporidian Trachipleistophora hominis (Williams et al, 2002). Although similar structures have not yet been observed in the microsporidian Encephalitozoon cuniculi, even this species contains genes of probable mitochondrial origin (Katinka et al, 2001).…”

Genome sequence and gene compaction of the eukaryote parasite Encephalitozoon cuniculi

“…A common feature is an arginine residue at -2 relative to the cleavage site, similar to presequences of mitochondrial and hydrogenosomal proteins 25 . The amitochondriate protozoan Entamoeba histolytica has recently been shown to contain a residual mitochondrion-derived organelle 26±28 that some authors have called mitosome 28 . Considering the set of potential E. cuniculi proteins usually associated with mitochondria, we propose that a cryptic organelle is also present in microsporidia (Fig.…”