apicoplast

GO:0020011 · Membrane organelle · Membrane bounded organelle · Proposed

The plastid organelle found in apicomplexans. [GO:0020011]

Has part: apicoplast membrane (GO:0160211)

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

Components

Component	Type	Part of / acts on	Grounding	Essential	Role
apicoplast membrane	Lipid	part of	`GO:0160211`	ESSENTIAL	The multiple lipid bilayers that form the apicoplast envelope and separate the plastid from the surrounding parasite cytoplasm. `DOI:10.1186/1475-2875-12-25` Lemgruber et al. 2013 used cryo-electron tomography to resolve four membranes around the Plasmodium falciparum apicoplast. `DOI:10.1098/rstb.2009.0273` Lim et al. 2010 review the four-membrane apicoplast envelope and protein targeting across it.
apicoplast Tic20 inner-membrane translocon	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	UNKNOWN	Innermost-membrane translocon required for import of nuclear-encoded proteins into the apicoplast. `DOI:10.1073/pnas.0803862105` van Dooren et al. 2008 localized Toxoplasma gondii Tic20 to the apicoplast and showed that TgTic20 disruption blocks apicoplast protein import.
apicoplast SELMA/ERAD-derived import machinery	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	UNKNOWN	Protein-import machinery at the second outermost membrane that uses ubiquitin and ERAD-like components to deliver nuclear-encoded cargo toward the apicoplast stroma. `DOI:10.1371/journal.ppat.1003426` Agrawal et al. 2013 identified an apicoplast-localized ubiquitylation system required for import of nuclear-encoded plastid proteins.
nuclear-encoded apicoplast metabolic enzymes	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	UNKNOWN	Imported enzymes that execute apicoplast pathways including MEP/DOXP isoprenoid precursor biosynthesis, fatty-acid synthesis, heme metabolism, and iron-sulfur-cluster synthesis. `DOI:10.1098/rstb.2009.0273` Lim et al. 2010 review imported nuclear-encoded apicoplast enzymes in fatty-acid, heme, iron-sulfur and isoprenoid precursor pathways. `DOI:10.1146/annurev-micro-092412-155741` van Dooren and Striepen 2013 review the apicoplast as a plastid carrying multiple parasite metabolic pathways that depend on nuclear-encoded imported proteins.

Taxonomic distribution

NCBITaxon:5794 Apicomplexa — VARIABLE: The apicoplast is present in many apicomplexan parasites, including Plasmodium and Toxoplasma, but has been lost in some lineages. [DOI:10.1016/j.ijpara.2016.08.005]

Canonical examples

NCBITaxon:5833 Plasmodium falciparum — Human malaria parasite in which IPP rescue showed that apicoplast isoprenoid precursor biosynthesis is essential in blood-stage growth. [DOI:10.1371/journal.pbio.1001138]
NCBITaxon:5811 Toxoplasma gondii — Apicomplexan model used to show that Tic20 is required for protein import into the plastid. [DOI:10.1073/pnas.0803862105]

Functions

nuclear-encoded protein import — Most apicoplast proteins are encoded in the nucleus and imported across the surrounding membranes using bipartite targeting signals and membrane translocons.
- DOI:10.1073/pnas.95.21.12352 Waller et al. 1998 demonstrated targeting of nuclear-encoded proteins to the plastid in Toxoplasma gondii and Plasmodium falciparum.
- DOI:10.1073/pnas.0803862105 van Dooren et al. 2008 showed that Toxoplasma Tic20 is essential for apicoplast protein import.
isoprenoid precursor biosynthesis — The Plasmodium falciparum apicoplast makes the isoprenoid precursor IPP during blood-stage parasite growth.
- DOI:10.1371/journal.pbio.1001138 Yeh and DeRisi 2011 showed that exogenous IPP rescues blood-stage P. falciparum lacking apicoplast function.

Mechanism graphs

Bipartite leaders route nuclear-encoded cargo into the apicoplast (FUNCTION)

Nuclear-encoded apicoplast proteins carry a bipartite leader that directs them into the secretory pathway and then through apicoplast membrane translocons, including SELMA/ERAD-derived machinery and the Tic20 inner-membrane translocon.

Subject	Predicate	Object	Evidence
nuclear-encoded apicoplast precursor proteins	carry	bipartite apicoplast targeting leader	`DOI:10.1073/pnas.95.21.12352` Waller et al. 1998 used plastid-targeted nuclear-encoded proteins from Toxoplasma and Plasmodium to demonstrate apicoplast targeting.
bipartite apicoplast targeting leader	targets cargo to	endomembrane trafficking pathway	`DOI:10.1098/rstb.2009.0273` Lim et al. 2010 review signal peptide and transit-peptide targeting requirements for luminal apicoplast proteins.
SELMA/ERAD-derived import machinery	translocates	nuclear-encoded apicoplast precursor proteins	`DOI:10.1371/journal.ppat.1003426` Agrawal et al. 2013 found that disrupting the apicoplast-localized ubiquitylation system blocked nuclear-encoded plastid protein import.
Tic20 inner-membrane translocon	translocates	nuclear-encoded apicoplast precursor proteins	`DOI:10.1073/pnas.0803862105` van Dooren et al. 2008 localized TgTic20 to the apicoplast and showed that TgTic20 disruption blocks protein import.
SELMA/ERAD-derived import machinery	resides in	apicoplast membrane	`DOI:10.1371/journal.ppat.1003426` Agrawal et al. 2013 characterized the import machinery as apicoplast localized.
Tic20 inner-membrane translocon	resides in	apicoplast membrane	`DOI:10.1073/pnas.0803862105` van Dooren et al. 2008 assigned TgTic20 to the apicoplast innermost membrane import step.
apicoplast membrane	bounds	apicoplast	`DOI:10.1186/1475-2875-12-25` Lemgruber et al. 2013 visualized four apicoplast membranes by cryo-electron tomography.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral protein-family groundings for the Tic20 and SELMA/ERAD-derived apicoplast import components. The curated papers identify organism-specific apicoplast import proteins, while exact source-neutral CURIEs for those apicoplast import component classes were not resolved.

Evidence

DOI:10.1073/pnas.95.21.12352 Waller et al. 1998, Nuclear-encoded proteins target to the plastid in Toxoplasma gondii and Plasmodium falciparum, Proceedings of the National Academy of Sciences.
DOI:10.1098/rstb.2009.0273 Lim et al. 2010, The evolution, metabolism and functions of the apicoplast, Philosophical Transactions of the Royal Society B.
DOI:10.1073/pnas.0803862105 van Dooren et al. 2008, Toxoplasma gondii Tic20 is essential for apicoplast protein import, Proceedings of the National Academy of Sciences.
DOI:10.1371/journal.ppat.1003426 Agrawal et al. 2013, An apicoplast localized ubiquitylation system is required for the import of nuclear-encoded plastid proteins, PLOS Pathogens.
DOI:10.1186/1475-2875-12-25 Lemgruber et al. 2013, Cryo-electron tomography reveals four-membrane architecture of the Plasmodium apicoplast, Malaria Journal.
DOI:10.1146/annurev-micro-092412-155741 van Dooren and Striepen 2013, The algal past and parasite present of the apicoplast, Annual Review of Microbiology.
DOI:10.1371/journal.pbio.1001138 Yeh and DeRisi 2011, Chemical rescue of malaria parasites lacking an apicoplast defines organelle function in blood-stage Plasmodium falciparum, PLOS Biology.
DOI:10.1016/j.ijpara.2016.08.005 McFadden and Yeh 2017, The apicoplast: now you see it, now you don't, International Journal for Parasitology.

Curation history

2026-09-10T02:28:54Z claude · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-10T02:30:16Z claude · EXPANDED_RECORD — Added GO apicoplast membrane parthood, membrane and import components, Apicomplexa taxonomic scope, Plasmodium and Toxoplasma canonical examples, protein-import and IPP functions, a mechanistic import graph, and an import-component grounding discussion.
2026-09-10T02:30:47Z claude · FIXED_DISCUSSION_ANCHORS — Scoped the apicoplast import grounding discussion attachments to component anchors and normalized the apicoplast membrane graph predicate.
2026-09-10T02:37:24Z claude · FIXED_GROUNDING_LABEL — Aligned GO:0160211 apicoplast membrane labels with the GO canonical.
2026-09-10T02:45:54Z claude · ADDRESS_REVIEW — Resolved #303 by downgrading non-structural apicoplast protein groups to unknown essentiality; resolved #304 by reclassifying the bipartite-leader import graph as FUNCTION; resolved #305 by scoping the Toxoplasma gondii canonical-example note to the Tic20 paper it cites.

Source: data/structures/membrane_organelle/apicoplast.yaml