apical complex
A group of cytoskeletal structures and associated membrane-bounded organelles at the anterior end of apicomplexan parasites that supports host-cell attachment, penetration, and parasite proliferation. [GO:0020007]
Has part: conoid (GO:0020010); polar ring of apical complex (GO:0020031); rhoptry (GO:0020008); microneme (GO:0020009)
Components
| Component | Type | Part of / acts on | Grounding | Genes | Stoichiometry | Essential | Role |
|---|---|---|---|---|---|---|---|
| apical-complex cytoskeletal proteins | Protein | part of | Reviewed label only (reviewed name; no accession asserted) | UNKNOWN | Cytoskeletal proteins that build and position apical structures such as the conoid and apical polar ring.
| ||
| apical secretory-organelle proteins | Protein | part of | Reviewed label only (reviewed name; no accession asserted) | UNKNOWN | Secretory proteins stored in micronemes and rhoptries before their ordered discharge during host-cell invasion.
|
Taxonomic distribution
NCBITaxon:5794Apicomplexa — COMMON: The apical complex is the eponymous anterior cytoskeletal and secretory apparatus of apicomplexan invasive stages, with lineage- and stage-specific variation in individual substructures. [DOI:10.1128/mmbr.00197-22]
Canonical examples
NCBITaxon:5811Toxoplasma gondii — Apicomplexan model in which the conoid/apical-complex cytoskeleton was partially purified for proteomic analysis. [DOI:10.1371/journal.ppat.0020013]
Functions
- host-cell invasion — The apical complex positions cytoskeletal and secretory parts that support attachment to and invasion of host cells by apicomplexan zoites.
DOI:10.1371/journal.ppat.0020013Hu et al. 2006 studied the Toxoplasma apical complex as a cytoskeletal invasion machine.DOI:10.1128/mmbr.00197-22Waller and Carruthers 2024 review apical-complex and secretory-organelle diversity in Myzozoa and Apicomplexa.
- ordered apical-organelle secretion — Micronemes and rhoptries at the apical complex discharge in an ordered sequence during invasion, coordinating attachment, moving-junction formation and vacuole establishment.
PMID:9208224Carruthers and Sibley 1997 showed that Toxoplasma micronemes, rhoptries and dense granules secrete sequentially during invasion.DOI:10.1038/nrmicro1800Boothroyd and Dubremetz 2008 review rhoptry secretion after host-cell attachment and at the start of invasion.
Mechanism graphs
Apical cytoskeletal and secretory parts coordinate invasion (FUNCTION)
The apical complex groups cytoskeletal structures such as the conoid and apical polar ring with apically positioned secretory organelles such as micronemes and rhoptries to coordinate host-cell invasion.
| Subject | Predicate | Object | Evidence |
|---|---|---|---|
| conoid | is part of | apical complex |
|
| polar ring of apical complex | is part of | apical complex |
|
| microneme | is part of | apical complex |
|
| rhoptry | is part of | apical complex |
|
| apical complex | supports | host-cell invasion |
|
Discussions
- CURATION_TODO (OPEN): Resolve exact source-neutral groundings for apical-complex cytoskeletal proteins and for the microneme/rhoptry secretory protein cohorts. The first apical-complex record links named substructures as parts and groups unrelated molecular constituents into two reviewed-label-only cohorts rather than guessing InterPro or Complex Portal CURIEs.
Evidence
DOI:10.1371/journal.ppat.0020013Hu et al. 2006, Cytoskeletal Components of an Invasion Machine--the Apical Complex of Toxoplasma gondii, PLOS Pathogens.PMID:9208224Carruthers and Sibley 1997, Sequential protein secretion from three distinct organelles of Toxoplasma gondii accompanies invasion of human fibroblasts, European Journal of Cell Biology.DOI:10.1073/pnas.2416602121Ren et al. 2024, Architecture of the Toxoplasma gondii apical polar ring and its role in gliding motility and invasion, Proceedings of the National Academy of Sciences.DOI:10.1038/nrmicro1800Boothroyd and Dubremetz 2008, Kiss and spit: the dual roles of Toxoplasma rhoptries, Nature Reviews Microbiology.DOI:10.1128/mmbr.00197-22Waller and Carruthers 2024, Adaptations and metabolic evolution of myzozoan protists across diverse lifestyles and environments, Microbiology and Molecular Biology Reviews.
Curation history
2026-09-10T12:52:03Zclaude · CREATED_RECORD — Scaffolded by scripts/new_record.py2026-09-10T12:52:35Zclaude · EXPANDED_RECORD — Added conoid, polar ring, rhoptry and microneme parts; cytoskeletal and secretory protein cohorts; Apicomplexa scope; Toxoplasma gondii as a canonical example; invasion and apical-organelle-secretion functions; a nonmechanistic apical-complex invasion graph; and a grounding TODO for exact apical-complex protein cohorts.2026-09-10T13:02:49Zclaude · ADDRESS_REVIEW — Addressed PR #368 review issues #369 and #370 by narrowing the Toxoplasma gondii canonical-example note to the Hu 2006 cytoskeletal evidence and removing the unsupported apical-complex-to-secretion coordination graph edge.