Mitosome

{{Short description|Cell organelle in a few species}} A '''mitosome''' (also called a ''crypton'' in early literature)<ref>{{cite journal | vauthors = Mai Z, Ghosh S, Frisardi M, Rosenthal B, Rogers R, Samuelson J | title = Hsp60 is targeted to a cryptic mitochondrion-derived organelle ("crypton") in the microaerophilic protozoan parasite Entamoeba histolytica | journal = Molecular and Cellular Biology | volume = 19 | issue = 3 | pages = 2198–2205 | date = March 1999 | pmid = 10022906 | pmc = 84012 | doi = 10.1128/MCB.19.3.2198 }}</ref> is a mitochondrion-related organelle (MRO)<ref name="Onuț-Brännström_2023">{{cite journal | vauthors = Onuț-Brännström I, Stairs CW, Campos KI, Thorén MH, Ettema TJ, Keeling PJ, Bass D, Burki F | display-authors = 6 | title = A Mitosome With Distinct Metabolism in the Uncultured Protist Parasite Paramikrocytos canceri (Rhizaria, Ascetosporea) | journal = Genome Biology and Evolution | volume = 15 | issue = 3 | date = March 2023 | pmid = 36790104 | doi = 10.1093/gbe/evad022 | pmc = 9998036 | veditors = Eme L }}</ref> 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,<ref name="Tovar993">{{cite journal | vauthors = Tovar J, Fischer A, Clark CG | title = The mitosome, a novel organelle related to mitochondria in the amitochondrial parasite Entamoeba histolytica | journal = Molecular Microbiology | volume = 32 | issue = 5 | pages = 1013–1021 | date = June 1999 | pmid = 10361303 | doi = 10.1046/j.1365-2958.1999.01414.x | doi-access = free }}</ref><ref name="Bakatselou033">{{cite journal | vauthors = Bakatselou C, Beste D, Kadri AO, Somanath S, Clark CG | title = Analysis of genes of mitochondrial origin in the genus Entamoeba | journal = The Journal of Eukaryotic Microbiology | volume = 50 | issue = 3 | pages = 210–214 | year = 2003 | pmid = 12836878 | doi = 10.1111/j.1550-7408.2003.tb00119.x | s2cid = 85169619 }}</ref> and mitosomes have also been identified in several species of Microsporidia<ref name="Williams023">{{cite journal | vauthors = Williams BA, Hirt RP, Lucocq JM, Embley TM | title = A mitochondrial remnant in the microsporidian Trachipleistophora hominis | journal = Nature | volume = 418 | issue = 6900 | pages = 865–869 | date = August 2002 | pmid = 12192407 | doi = 10.1038/nature00949 | bibcode = 2002Natur.418..865W | s2cid = 4358253 }}</ref><ref name="Goldberg043">{{cite journal | vauthors = Goldberg AV, Molik S, Tsaousis AD, Neumann K, Kuhnke G, Delbac F, Vivares CP, Hirt RP, Lill R, Embley TM | display-authors = 6 | title = Localization and functionality of microsporidian iron-sulphur cluster assembly proteins | journal = Nature | volume = 452 | issue = 7187 | pages = 624–628 | date = April 2008 | pmid = 18311129 | doi = 10.1038/nature06606 | bibcode = 2008Natur.452..624G | s2cid = 4431368 }}</ref> and in ''Giardia intestinalis''.<ref name="Tovar05">{{cite journal | vauthors = Tovar J, León-Avila G, Sánchez LB, Sutak R, Tachezy J, van der Giezen M, Hernández M, Müller M, Lucocq JM | display-authors = 6 | title = Mitochondrial remnant organelles of Giardia function in iron-sulphur protein maturation | journal = Nature | volume = 426 | issue = 6963 | pages = 172–176 | date = November 2003 | pmid = 14614504 | doi = 10.1038/nature01945 | bibcode = 2003Natur.426..172T | s2cid = 4402808 }}</ref>

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.<ref name="Onuț-Brännström_2023" /> The functions of mitosomes, while varied, have not yet been well characterized,<ref name="Onuț-Brännström_2023" /> but they may be associated with sulfate metabolism and biosynthesis of phospholipids and Fe–S clusters.<ref name="Onuț-Brännström_2023" /><ref name="Goldberg043" /><ref name="Mi-ichi_2009">{{cite journal | vauthors = Mi-ichi F, Abu Yousuf M, Nakada-Tsukui K, Nozaki T | title = Mitosomes in Entamoeba histolytica contain a sulfate activation pathway | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 106 | issue = 51 | pages = 21731–21736 | date = December 2009 | pmid = 19995967 | pmc = 2799805 | doi = 10.1073/pnas.0907106106 | bibcode = 2009PNAS..10621731M | doi-access = free }}</ref><ref name="Santos_2018">{{cite journal | vauthors = Santos HJ, Makiuchi T, Nozaki T | title = Reinventing an Organelle: The Reduced Mitochondrion in Parasitic Protists | journal = Trends in Parasitology | volume = 34 | issue = 12 | pages = 1038–1055 | date = December 2018 | pmid = 30201278 | doi = 10.1016/j.pt.2018.08.008 | s2cid = 52183593 | doi-access = free }}</ref> Mitosomes, like other MROs, likely evolved from mitochondria,<ref name="Tovar993" /><ref name="Dolezal_2019">{{cite book |title=Hydrogenosomes and Mitosomes: Mitochondria of Anaerobic Eukaryotes |vauthors=Dolezal P, Makki A, Dyall SD |date=2019 |publisher=Springer International Publishing |isbn=978-3-030-17941-0 |veditors=Tachezy J |series=Microbiology Monographs |volume=9 |place=Cham |pages=31–84 |language=en |chapter=Protein Import into Hydrogenosomes and Mitosomes |doi=10.1007/978-3-030-17941-0_3}}</ref> based on similarities in structure, function, and biochemical signaling pathways,<ref name="Tovar993" /><ref name="Bakatselou033" /><ref name="Williams023" /><ref name="Goldberg043" /><ref name="Dolezal_2019" /> and may have convergently evolved across eukaryote lineages.<ref name="Onuț-Brännström_2023" /><ref name="Santos_2018" />

== Structure and function == Mitosomes are membrane-bound organelles closely related to mitochondria in structure, though functional overlap is limited.<ref name="Onuț-Brännström_2023" /><ref name="Tovar993" /> Unlike mitochondria, mitosomes do not have genes within them; instead, the genes for mitosomal components are contained in the nuclear genome.<ref name="Tovar993" /> An early report suggested the presence of DNA in this organelle,<ref name="Ghosh002">{{cite journal | vauthors = Ghosh S, Field J, Rogers R, Hickman M, Samuelson J | title = The Entamoeba histolytica mitochondrion-derived organelle (crypton) contains double-stranded DNA and appears to be bound by a double membrane | journal = Infection and Immunity | volume = 68 | issue = 7 | pages = 4319–4322 | date = July 2000 | pmid = 10858251 | pmc = 101756 | doi = 10.1128/IAI.68.7.4319-4322.2000 }}</ref> but subsequent research has shown this not to be the case.<ref name="Leon042">{{cite journal | vauthors = León-Avila G, Tovar J | title = Mitosomes of Entamoeba histolytica are abundant mitochondrion-related remnant organelles that lack a detectable organellar genome | journal = Microbiology | volume = 150 | issue = Pt 5 | pages = 1245–1250 | date = May 2004 | pmid = 15133087 | doi = 10.1099/mic.0.26923-0 | doi-access = free }}</ref> Many proteins within mitosomes (e.g., in ''Giardia intestinalis'') have poorly resolved or unexplored functions which are likely related to metabolism and protein transport.<ref>{{cite journal | vauthors = Martincová E, Voleman L, Pyrih J, Žárský V, Vondráčková P, Kolísko M, Tachezy J, Doležal P | display-authors = 6 | title = Probing the Biology of Giardia intestinalis Mitosomes Using In Vivo Enzymatic Tagging | journal = Molecular and Cellular Biology | volume = 35 | issue = 16 | pages = 2864–2874 | date = August 2015 | pmid = 26055323 | pmc = 4508323 | doi = 10.1128/MCB.00448-15 }}</ref> Unlike mitochondria, mitosomes appear to lack electron transport chains, N-terminal targeting sequences, and the ability to fuse with each other.<ref name="Santos_2018" />

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 (oxidative phosphorylation via aerobic respiration, haem biosynthesis) while they do display proteins required for Fe–S cluster biosynthesis (like frataxin, cysteine desulfurase, Isu1 and a mitochondrial Hsp70).<ref name="Onuț-Brännström_2023" /><ref name="Goldberg043" /><ref name="Santos_2018" /> Additionally, modified mitosomes in the intracellular parasitic protist ''Paramikrocytos canceri'' may biosynthesize phospholipids and support glycolytic ATP production, based on genomic and transcriptomic analysis.<ref name="Onuț-Brännström_2023" /> Mitosomes may also facilitate metabolic activation of sulfates in some eukaryotes, based on analyses of enzymes from mitosomes in ''Entamoeba histolytica'' and ''Mastigamoeba balamuthi''.<ref name="Mi-ichi_2009" /><ref name="Mi-ichi_2015">{{cite journal | vauthors = Mi-ichi F, Miyamoto T, Takao S, Jeelani G, Hashimoto T, Hara H, Nozaki T, Yoshida H | display-authors = 6 | title = Entamoeba mitosomes play an important role in encystation by association with cholesteryl sulfate synthesis | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 112 | issue = 22 | pages = E2884–E2890 | date = June 2015 | pmid = 25986376 | pmc = 4460517 | doi = 10.1073/pnas.1423718112 | bibcode = 2015PNAS..112E2884M | doi-access = free }}</ref> 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,<ref name="Mi-ichi_2015" /> though the role of mitosomes in pathogenicity is less clear for many other parasitic eukaryotes.<ref name="Santos_2018" />

== 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.<ref name="Santos_2018" /><ref name="Dolezal_2019" /> Like mitochondria, they have a double membrane and most proteins are delivered to them by a targeting sequence of amino acids.<ref name="Tovar993" /><ref name="Williams023" /><ref name="Goldberg043" /> The targeting sequence is similar to that used for mitochondria and true mitochondrial presequences will deliver proteins to mitosomes.<ref name="Tovar993" /> A number of proteins associated with mitosomes have been shown to be closely related to those of mitochondria<ref name="Bakatselou033" /> and hydrogenosomes.<ref name="Dolezal06">{{cite journal | vauthors = Dolezal P, Smíd O, Rada P, Zubácová Z, Bursać D, Suták R, Nebesárová J, Lithgow T, Tachezy J | display-authors = 6 | title = Giardia mitosomes and trichomonad hydrogenosomes share a common mode of protein targeting | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 102 | issue = 31 | pages = 10924–10929 | date = August 2005 | pmid = 16040811 | pmc = 1182405 | doi = 10.1073/pnas.0500349102 | bibcode = 2005PNAS..10210924D | doi-access = free }}</ref>

Mitosomes appear to have degeneratively evolved from mitochondria multiple times across eukaryote lineages,<ref name="Onuț-Brännström_2023" /> and their "mosaic" biochemistry in ''Entamoeba histolytica'' may reflect a composite ancestry involving both eukaryotes and proteobacteria.<ref name="Mi-ichi_2009" /> 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.<ref>{{cite book | vauthors = Zimorski V, Martin WF | series = Microbiology Monographs | chapter = The Evolution of Oxygen-Independent Energy Metabolism in Eukaryotes with Hydrogenosomes and Mitosomes |date=2019 | volume = 9 | veditors = Tachezy J | title = Hydrogenosomes and Mitosomes: Mitochondria of Anaerobic Eukaryotes |pages=7–29 |place=Cham |publisher=Springer International Publishing | doi = 10.1007/978-3-030-17941-0_2 |isbn=978-3-030-17940-3 | s2cid = 202026532 }}</ref>

== References == {{reflist|35em}}

{{Protist|state=expanded}} {{Self-replicating organic structures|state=collapsed}}

Category:Eukaryotic cell anatomy Category:Organelles