mitosome

GO:0032047 · Membrane organelle · Membrane bounded organelle · Proposed

A double-membrane-bounded organelle that functions in iron-sulfur protein maturation; evolutionarily derived from mitochondria. The mitosome has been detected only in anaerobic or microaerophilic organisms that do not have mitochondria, such as Entamoeba histolytica, Giardia intestinalis and several species of Microsporidia. These organisms are not capable of gaining energy from oxidative phosphorylation, which is normally performed by mitochondria. [GO:0032047]

Part of: GO:0005737 — cytoplasm (no local record)

Has part: mitosome envelope (cellstructuremech:mitosome_envelope); mitosome matrix (cellstructuremech:mitosome_matrix)

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
mitosomal iron-sulfur cluster assembly machinery	Protein	part of	Reviewed label only (reviewed name; no accession asserted)			UNKNOWN	Mitochondrial-type factors that assemble iron-sulfur clusters in Giardia and microsporidian mitosomes. `DOI:10.1038/nature01945` Tovar et al. 2003 showed that Giardia mitochondrial remnant organelles function in iron-sulfur protein maturation. `DOI:10.1038/nature06606` Goldberg et al. 2008 localized functional iron-sulfur cluster assembly proteins to microsporidian mitosomes.
mitosomal protein-import machinery	Protein	acts on	Reviewed label only (reviewed name; no accession asserted)			UNKNOWN	Machinery that imports nuclear-encoded mitosomal proteins into the reduced mitochondrion-related organelle. `DOI:10.1073/pnas.0500349102` Dolezal et al. 2005 found that Giardia mitosomes and trichomonad hydrogenosomes share a protein-targeting mode. `DOI:10.1038/nature01945` Tovar et al. 2003 detected Giardia ISC proteins inside mitosomes, implying organelle import of nuclear-encoded machinery.

Taxonomic distribution

NCBITaxon:2759 Eukaryota — RARE: Mitosomes occur patchily in anaerobic or microaerophilic microbial eukaryotes that have reduced mitochondria. [DOI:10.1111/jeu.12922]
NCBITaxon:5741 Giardia duodenalis — COMMON: Giardia mitosomes have been used to define Fe-S maturation and protein-targeting functions in a reduced mitochondrion-related organelle. [DOI:10.1038/nature01945]
NCBITaxon:5759 Entamoeba histolytica — COMMON: The early mitosome record was defined from Entamoeba histolytica trophozoites. [DOI:10.1046/j.1365-2958.1999.01414.x]
NCBITaxon:6029 Microsporidia — VARIABLE: Microsporidian mitochondrion remnants have been described in Trachipleistophora and functionally tested in Encephalitozoon. [DOI:10.1038/nature06606]

Canonical examples

NCBITaxon:5741 Giardia duodenalis — Diplomonad parasite whose mitosomes experimentally support the ISC-centered function graph. [DOI:10.1038/nature01945]

Functions

mitosomal iron-sulfur cluster assembly — Mitosomes retain imported mitochondrial-type ISC machinery that supports iron-sulfur protein maturation.
- DOI:10.1038/nature01945 Tovar et al. 2003 showed that Giardia mitosomes function in iron-sulfur protein maturation.
- DOI:10.1038/nature06606 Goldberg et al. 2008 showed that microsporidian mitosomal ISC proteins are functional.
mitosomal protein import — Nuclear-encoded proteins are imported into the mitosome, which lacks its own organellar genome.
- DOI:10.1073/pnas.0500349102 Dolezal et al. 2005 compared targeting signals in Giardia mitosomes.
- DOI:10.1038/nature01945 Tovar et al. 2003 localized nuclear-encoded ISC machinery to Giardia mitosomes.

Mechanism graphs

Mitosomal import supports iron-sulfur cluster assembly (FUNCTION)

A double mitosomal envelope encloses imported mitochondrial-type ISC proteins that drive iron-sulfur cluster assembly in the reduced organelle.

Subject	Predicate	Object	Evidence
mitosomal double-membrane envelope	bounds	mitosome	`DOI:10.1046/j.1365-2958.1999.01414.x` Tovar et al. 1999 defined the Entamoeba mitosome as a mitochondrion-related organelle. `uniprot.location:SL-0438` — Mitosome envelope UniProt SL-0438 identifies the mitosome envelope as the inner and outer mitosomal membranes plus intermembrane space.
mitosomal protein-import machinery	imports	mitosomal iron-sulfur cluster assembly machinery	`DOI:10.1073/pnas.0500349102` Dolezal et al. 2005 tested Giardia mitosomal protein targeting using N-terminal targeting sequences.
mitosomal iron-sulfur cluster assembly machinery	resides in	mitosome	`DOI:10.1038/nature06606` Goldberg et al. 2008 localized functional ISC proteins to microsporidian mitosomes.
mitosomal iron-sulfur cluster assembly machinery	supports	iron-sulfur cluster assembly	`DOI:10.1038/nature01945` Tovar et al. 2003 showed that Giardia mitosomes function in iron-sulfur protein maturation.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral groundings for mitosomal ISC factors and protein-import machinery. The mitosome record still uses reviewed-label-only component groups for ISC factors and protein-import machinery because exact protein-family or complex-level groundings were not curated.

Evidence

DOI:10.1046/j.1365-2958.1999.01414.x Tovar et al. 1999, The mitosome, a novel organelle related to mitochondria in the amitochondrial parasite Entamoeba histolytica, Molecular Microbiology.
DOI:10.1038/nature01945 Tovar et al. 2003, Mitochondrial remnant organelles of Giardia function in iron-sulphur protein maturation, Nature.
DOI:10.1038/nature00949 Williams et al. 2002, A mitochondrial remnant in the microsporidian Trachipleistophora hominis, Nature.
DOI:10.1038/nature06606 Goldberg et al. 2008, Localization and functionality of microsporidian iron-sulphur cluster assembly proteins, Nature.
DOI:10.1073/pnas.0500349102 Dolezal et al. 2005, Giardia mitosomes and trichomonad hydrogenosomes share a common mode of protein targeting, Proceedings of the National Academy of Sciences.
DOI:10.1111/jeu.12922 Tachezy 2022, Hydrogenosomes and mitosomes: Mitochondria of anaerobic eukaryotes, Journal of Eukaryotic Microbiology.
uniprot.location:SL-0441 — Mitosome matrix UniProt Subcellular Location entry SL-0441 identifies the mitosome matrix and places it under the mitosome location.

Curation history

2026-09-10T03:44:22Z claude · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-10T03:44:53Z claude · EXPANDED_RECORD — Added parentage, double-membrane envelope, ISC and import component groups, rare eukaryotic, Entamoeba and Microsporidia taxonomic scope, Entamoeba histolytica as a canonical example, Fe-S assembly and protein import functions, an ISC assembly graph, and grounding TODOs for mitosomal substructures and grouped protein machinery.
2026-09-10T03:52:33Z claude · ADDRESSED_PR_REVIEW — Addressed PR #314 review issues #315, #316 and #317 by adding Giardia duodenalis as a taxonomic distribution and canonical example, citing Dolezal et al. 2005 on Giardia mitosomal protein import, and replacing the unused Entamoeba sulfate-activation citation.
2026-09-13T19:09:20Z codex · ADDRESSED_CURATION_TODO — Replaced the reviewed-label-only mitosomal envelope component with a has_part link to cellstructuremech:mitosome_envelope, grounded the ISC graph envelope node to the new exact record, and narrowed the remaining component-grounding TODO to mitosomal protein groups.
2026-09-13T20:16:06Z codex · ADD_CHILD_RECORD — Added cellstructuremech:mitosome_matrix as a mitosome has_part child based on the exact UniProt SL-0441 mitosome matrix record.

Source: data/structures/membrane_organelle/mitosome.yaml