2
Bacterial-type oxygen detoxification and iron-sulfur cluster assembly in amoebal relict mitochondria.
Cell Microbiol. 2010 Mar; 12(3):331-42
All selected articles haveThis article has been added to your saved articles
You can follow/unfollow articles via MyF1000 or via the article or browse pages.
12 Jan 2010
Controversial, New Finding
DOI: 10.3410/f.1387968.861069
The function of the mitosome (a degenerate mitochondrion) of Entamoeba histolytica remained obscure even after the genome of this parasite was sequenced. This paper ascribes one important function to the organelle - Fe-S cluster assembly. Along with a second recent paper {1}, the present publication finally...Continue reading
The function of the mitosome (a degenerate mitochondrion) of Entamoeba histolytica remained obscure even after the genome of this parasite was sequenced. This paper ascribes one important function to the organelle - Fe-S cluster assembly. Along with a second recent paper {1}, the present publication finally gives us reasons for the retention of this organelle and the associated genes.
Our group predicted the existence of the mitosome of E. histolytica 15 years ago {2} and we and others initially identified it 10 years ago {3,4}, but its function remained obscure. The genome sequence did not identify any metabolic pathways that were unequivocally located in the organelle, although a small number of organellar genes could be identified - encoding chaperonins and a mitochondrial family transporter, for example {5}. Mitosomes in Giardia were in the meantime shown to function in Fe-S cluster synthesis {6} and some of the same authors have here shown that the same is true of the E. histolytica organelle. However, the picture is not quite as clear-cut as in Giardia, as the two E. histolytica Fe-S synthesis proteins localised - NifS and NifU - are still predominantly cytoplasmic in location. Mitosomes make up only 1.7% of the cell volume but quantitative immuno-electron microscopy shows the two proteins to be 10-fold more concentrated in mitosomes compared to the cytosol. The authors also identified rubrerythrin, a peroxidase with a Fe-S cluster, as a mitosomal protein.
In conclusion it appears that Fe-S cluster synthesis is one, but probably not the only, function of mitosomes. Why the Nif proteins have such an odd distribution and what their function is in the cytosol remains to be determined.
Our group predicted the existence of the mitosome of E. histolytica 15 years ago {2} and we and others initially identified it 10 years ago {3,4}, but its function remained obscure. The genome sequence did not identify any metabolic pathways that were unequivocally located in the organelle, although a small number of organellar genes could be identified - encoding chaperonins and a mitochondrial family transporter, for example {5}. Mitosomes in Giardia were in the meantime shown to function in Fe-S cluster synthesis {6} and some of the same authors have here shown that the same is true of the E. histolytica organelle. However, the picture is not quite as clear-cut as in Giardia, as the two E. histolytica Fe-S synthesis proteins localised - NifS and NifU - are still predominantly cytoplasmic in location. Mitosomes make up only 1.7% of the cell volume but quantitative immuno-electron microscopy shows the two proteins to be 10-fold more concentrated in mitosomes compared to the cytosol. The authors also identified rubrerythrin, a peroxidase with a Fe-S cluster, as a mitosomal protein.
In conclusion it appears that Fe-S cluster synthesis is one, but probably not the only, function of mitosomes. Why the Nif proteins have such an odd distribution and what their function is in the cytosol remains to be determined.
References
1.
Mitosomes in Entamoeba histolytica contain a sulfate activation pathway.
Proc Natl Acad Sci USA 2009 Dec 22; 51(106):21731-6
PMID: 19995967
2.
Direct evidence for secondary loss of mitochondria in Entamoeba histolytica.
Proc Natl Acad Sci USA 1995 Jul 3; 14(92):6518-21
PMID: 7604025
3.
The mitosome, a novel organelle related to mitochondria in the amitochondrial parasite Entamoeba histolytica.
Mol Microbiol 1999 Jun; 5(32):1013-21
PMID: 10361303
4.
The Entamoeba histolytica mitochondrion-derived organelle (crypton) contains double-stranded DNA and appears to be bound by a double membrane.
Infect Immun 2000 Jul; 7(68):4319-22
PMID: 10858251
5.
Structure and content of the Entamoeba histolytica genome.
Adv Parasitol 2007; (65):51-190
PMID: 18063096
6.
Mitochondrial remnant organelles of Giardia function in iron-sulphur protein maturation.
Nature 2003 Nov 13; 6963(426):172-6
PMID: 14614504
Disclosures
None declared
Add Comment
Clark C: F1000Prime Recommendation of [Maralikova B et al., Cell Microbiol 2010, 12(3):331-42]. In F1000Prime, 12 Jan 2010; DOI: 10.3410/f.1387968.861069. F1000Prime.com/1387968#eval861069
F1000Prime Recommendations, Dissents and Comments for [Maralikova B et al., Cell Microbiol 2010, 12(3):331-42]. In F1000Prime, 25 May 2013; F1000Prime.com/1387968
Only registered/signed-in users can make comments.
Sign in or Subscribe to create your user account and join the discussion.
Sign in or Subscribe to create your user account and join the discussion.
No comments yet.
The assembly of vital reactive iron-sulfur (Fe-S) cofactors in eukaryotes is mediated by proteins inherited from the original mitochondrial endosymbiont. Uniquely among eukaryotes, however, Entamoeba and Mastigamoeba lack such mitochondrial-type Fe-S cluster assembly proteins and possess instead an analogous bacterial-type system acquired by lateral gene transfer. Here we demonstrate, using immunomicroscopy and biochemical methods, that beyond their predicted cytosolic distribution the bacterial-type Fe-S cluster assembly proteins NifS and NifU have been recruited to function within the relict mitochondrial organelles (mitosomes) of Entamoeba histolytica. Both Nif proteins are 10-fold more concentrated within mitosomes compared with their cytosolic distribution suggesting that active Fe-S protein maturation occurs in these organelles. Quantitative immunoelectron microscopy showed that amoebal mitosomes are minute but highly abundant cellular structures that occupy up to 2% of the total cell volume. In addition, protein colocalization studies allowed identification of the amoebal hydroperoxide detoxification enzyme rubrerythrin as a mitosomal protein. This protein contains functional Fe-S centres and exhibits peroxidase activity in vitro. Our findings demonstrate the role of analogous protein replacement in mitochondrial organelle evolution and suggest that the relict mitochondrial organelles of Entamoeba are important sites of metabolic activity that function in Fe-S protein-mediated oxygen detoxification.
DOI: 10.1111/j.1462-5822.2009.01397.x
PMID: 19888992
