Biology:Mitosome
A mitosome (also called a crypton in early literature)[1] is a mitochondrion-related organelle (MRO)[2] found in a variety of parasitic unicellular eukaryotes, such as members of the supergroup Excavata. The mitosome was first discovered in 1999 in Entamoeba histolytica, an intestinal parasite of humans,[3][4] and mitosomes have also been identified in several species of Microsporidia[5][6] and in Giardia intestinalis.[7]
The mitosome has been detected only in anaerobic or microaerophilic eukaryotes which do not have fully developed mitochondria, and hence do not have the capability of gaining energy from mitochondrial oxidative phosphorylation.[2] The functions of mitosomes, while varied, have not yet been well characterized,[2] but they may be associated with sulfate metabolism and biosynthesis of phospholipids and Fe–S clusters.[2][6][8][9] Mitosomes, like other MROs, likely evolved from mitochondria,[3][10] based on similarities in structure, function, and biochemical signaling pathways,[3][4][5][6][10] and may have convergently evolved across eukaryote lineages.[2][9]
Structure and function
Mitosomes are membrane-bound organelles closely related to mitochondria in structure, though functional overlap is limited.[2][3] Unlike mitochondria, mitosomes do not have genes within them - instead, the genes for mitosomal components are contained in the nuclear genome.[3] An early report suggested the presence of DNA in this organelle,[11] but subsequent research has shown this not to be the case.[12] Many proteins within mitosomes (e.g., in Giardia intestinalis) have poorly resolved or unexplored functions which are likely related to metabolism and protein transport.[13] Unlike mitochondria, mitosomes appear to lack electron transport chains, N-terminal targeting sequences, and the ability to fuse with each other.[9]
Current knowledge indicates mitosomes probably play a role in Fe–S cluster assembly, since they do not display any of the proteins involved in other major mitochondrial functions (aerobic respiration via oxidative phosphorylation, haem biosynthesis) while they do display proteins required for Fe–S cluster biosynthesis (like frataxin, cysteine desulfurase, Isu1 and a mitochondrial Hsp70).[2][6][9] Additionally, modified mitosomes in the intracellular parasitic protist Paramikrocytos canceri may biosynthesize phospholipids and support glycolytic ATP production, based on genomic and transcriptomic analysis.[2] Mitosomes may also facilitate metabolic activation of sulfates in some eukaryotes, based on analyses of enzymes from mitosomes in Entamoeba histolytica and Mastigamoeba balamuthi.[8][14] Recent work indicates that mitosomes participate in the transformation of Entamoeba histolytica trophozoites into cysts, thereby playing a key role in the pathogenic life cycle of this organism,[14] though the role of mitosomes in pathogenicity is less clear for many other parasitic eukaryotes.[9]
Origin and evolution
In the most widely accepted view, mitosomes are ultimately derived from mitochondria, and commonalities between the protein transport and signaling networks of mitochondria, hydrogenosomes (a related class of MROs), and mitosomes have been interpreted as relics of their common endosymbiotic origin.[9][10] Like mitochondria, they have a double membrane and most proteins are delivered to them by a targeting sequence of amino acids.[3][5][6] The targeting sequence is similar to that used for mitochondria and true mitochondrial presequences will deliver proteins to mitosomes.[3] A number of proteins associated with mitosomes have been shown to be closely related to those of mitochondria[4] and hydrogenosomes.[15]
Mitosomes appear to have degeneratively evolved from mitochondria multiple times across eukaryote lineages,[2] and their "mosaic" biochemistry in Entamoeba histolytica may reflect a composite ancestry involving both eukaryotes and proteobacteria.[8] It has been proposed that MROs such as mitosomes evolved in anoxic marine environments which predominated during the Proterozoic, thus explaining their anaerobic metabolic functionality.[16]
References
- ↑ "Hsp60 is targeted to a cryptic mitochondrion-derived organelle ("crypton") in the microaerophilic protozoan parasite Entamoeba histolytica". Molecular and Cellular Biology 19 (3): 2198–2205. March 1999. doi:10.1128/MCB.19.3.2198. PMID 10022906.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 "A Mitosome With Distinct Metabolism in the Uncultured Protist Parasite Paramikrocytos canceri (Rhizaria, Ascetosporea)". Genome Biology and Evolution 15 (3). March 2023. doi:10.1093/gbe/evad022. PMID 36790104.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 "The mitosome, a novel organelle related to mitochondria in the amitochondrial parasite Entamoeba histolytica". Molecular Microbiology 32 (5): 1013–1021. June 1999. doi:10.1046/j.1365-2958.1999.01414.x. PMID 10361303.
- ↑ 4.0 4.1 4.2 "Analysis of genes of mitochondrial origin in the genus Entamoeba". The Journal of Eukaryotic Microbiology 50 (3): 210–214. 2003. doi:10.1111/j.1550-7408.2003.tb00119.x. PMID 12836878.
- ↑ 5.0 5.1 5.2 "A mitochondrial remnant in the microsporidian Trachipleistophora hominis". Nature 418 (6900): 865–869. August 2002. doi:10.1038/nature00949. PMID 12192407. Bibcode: 2002Natur.418..865W.
- ↑ 6.0 6.1 6.2 6.3 6.4 "Localization and functionality of microsporidian iron-sulphur cluster assembly proteins". Nature 452 (7187): 624–628. April 2008. doi:10.1038/nature06606. PMID 18311129. Bibcode: 2008Natur.452..624G.
- ↑ "Mitochondrial remnant organelles of Giardia function in iron-sulphur protein maturation". Nature 426 (6963): 172–176. November 2003. doi:10.1038/nature01945. PMID 14614504. Bibcode: 2003Natur.426..172T.
- ↑ 8.0 8.1 8.2 "Mitosomes in Entamoeba histolytica contain a sulfate activation pathway". Proceedings of the National Academy of Sciences of the United States of America 106 (51): 21731–21736. December 2009. doi:10.1073/pnas.0907106106. PMID 19995967. Bibcode: 2009PNAS..10621731M.
- ↑ 9.0 9.1 9.2 9.3 9.4 9.5 "Reinventing an Organelle: The Reduced Mitochondrion in Parasitic Protists". Trends in Parasitology 34 (12): 1038–1055. December 2018. doi:10.1016/j.pt.2018.08.008. PMID 30201278.
- ↑ 10.0 10.1 10.2 "Protein Import into Hydrogenosomes and Mitosomes" (in en). Hydrogenosomes and Mitosomes: Mitochondria of Anaerobic Eukaryotes. Microbiology Monographs. 9. Cham: Springer International Publishing. 2019. pp. 31–84. doi:10.1007/978-3-030-17941-0_3. ISBN 978-3-030-17941-0.
- ↑ "The Entamoeba histolytica mitochondrion-derived organelle (crypton) contains double-stranded DNA and appears to be bound by a double membrane". Infection and Immunity 68 (7): 4319–4322. July 2000. doi:10.1128/IAI.68.7.4319-4322.2000. PMID 10858251.
- ↑ "Mitosomes of Entamoeba histolytica are abundant mitochondrion-related remnant organelles that lack a detectable organellar genome". Microbiology 150 (Pt 5): 1245–1250. May 2004. doi:10.1099/mic.0.26923-0. PMID 15133087.
- ↑ "Probing the Biology of Giardia intestinalis Mitosomes Using In Vivo Enzymatic Tagging". Molecular and Cellular Biology 35 (16): 2864–2874. August 2015. doi:10.1128/MCB.00448-15. PMID 26055323.
- ↑ 14.0 14.1 "Entamoeba mitosomes play an important role in encystation by association with cholesteryl sulfate synthesis". Proceedings of the National Academy of Sciences of the United States of America 112 (22): E2884–E2890. June 2015. doi:10.1073/pnas.1423718112. PMID 25986376. Bibcode: 2015PNAS..112E2884M.
- ↑ "Giardia mitosomes and trichomonad hydrogenosomes share a common mode of protein targeting". Proceedings of the National Academy of Sciences of the United States of America 102 (31): 10924–10929. August 2005. doi:10.1073/pnas.0500349102. PMID 16040811. Bibcode: 2005PNAS..10210924D.
- ↑ "The Evolution of Oxygen-Independent Energy Metabolism in Eukaryotes with Hydrogenosomes and Mitosomes". Hydrogenosomes and Mitosomes: Mitochondria of Anaerobic Eukaryotes. Microbiology Monographs. 9. Cham: Springer International Publishing. 2019. pp. 7–29. doi:10.1007/978-3-030-17941-0_2. ISBN 978-3-030-17940-3.
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