conoid

GO:0020010 · Cytoskeleton · Other · Proposed

A spiral cytoskeletal structure located at the apical end of the apical complex in some apicomplexan parasites. Fibers form a left-handed spiral, and are comprised of tubulin protofilaments organized in a ribbon-like structure that differs from the conventional tubular structure characteristic of microtubules. [GO:0020010]

Part of: GO:0005856 — cytoskeleton (no local record); apical complex (GO:0020007)

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

Components

Taxonomic distribution

• NCBITaxon:2759 Eukaryota — RARE: Conoids are apicomplexan cytoskeletal structures rather than conserved eukaryotic cytoskeleton features. [DOI:10.1371/journal.pbio.3001081]
• NCBITaxon:5811 Toxoplasma gondii — COMMON: Toxoplasma tachyzoites have the spiral ribbon-tubulin conoid body defined here. This occurrence is distinct from broader conoid-complex protein conservation. [DOI:10.1083/jcb.200112086]

Canonical examples

• NCBITaxon:5811 Toxoplasma gondii — Apicomplexan model in which the unusual tubulin polymers of the conoid were experimentally studied. [DOI:10.1083/jcb.200112086]

Functions

• apical cytoskeletal scaffolding — The conoid forms a spiral tubulin-based scaffold at the apex of the apical complex.
  • DOI:10.1083/jcb.200112086 Hu et al. 2002 resolved Toxoplasma conoid fibers as tubulin protofilament ribbons organized into a spiral.
• conoid-associated host cell entry and exit — The conoid-associated MyoH motor supports Toxoplasma gliding motility, host-cell entry, and host-cell exit.
  • DOI:10.1371/journal.ppat.1005388 Graindorge et al. 2016 found that MyoH is indispensable for Toxoplasma entry and exit from host cells.

Mechanism graphs

Tubulin conoid fibers and MyoH support parasite entry and exit (FUNCTION)

Tubulin protofilament ribbons form the spiral conoid body at the apical complex. The associated MyoH motor supports Toxoplasma entry into and exit from host cells; heterogeneous whole-complex proteomic cohorts are not asserted as body constituents.

Discussions

• CURATION_TODO (OPEN): Resolve exact source-neutral groundings for conoid tubulin fibers, conserved conoid complex proteins, and MyoH. The first conoid record keeps Toxoplasma-localized protein cohorts label-only because no exact cross-source protein-family CURIE was curated for the unusual conoid tubulin polymer, the conserved conoid proteome, or apicomplexan MyoH.
• INTERPRETATION (RESOLVED): Distinguish the spiral conoid body from the larger conoid-complex proteome. Hu 2006 enriched apical cytoskeletal preparations contain candidate proteins, not a pure inventory of conoid-body constituents. Koreny 2021 directly resolves distinct body, base, canopy and APR locations and documents reduced conoid-derived ring structures in Plasmodium. Homology or broad complex membership does not put every protein inside the ribbon-tubulin body or establish majority prevalence of that morphology.

Evidence

• DOI:10.1083/jcb.200112086 Hu et al. 2002, A novel polymer of tubulin forms the conoid of Toxoplasma gondii, Journal of Cell Biology.
• DOI:10.1371/journal.ppat.0020013 Hu et al. 2006, Cytoskeletal Components of an Invasion Machine--the Apical Complex of Toxoplasma gondii, PLOS Pathogens.
• DOI:10.1371/journal.pbio.3001081 Koreny et al. 2021, Molecular characterization of the conoid complex in Toxoplasma reveals its conservation in all apicomplexans, including Plasmodium species, PLOS Biology.
• DOI:10.1371/journal.ppat.1005388 Graindorge et al. 2016, The Conoid Associated Motor MyoH Is Indispensable for Toxoplasma gondii Entry and Exit from Host Cells, PLOS Pathogens.

Curation history

• 2026-09-10T05:32:48Z claude · CREATED_RECORD — Scaffolded by scripts/new_record.py
• 2026-09-10T05:34:23Z claude · EXPANDED_RECORD — Added cytoskeleton and apical-complex parthood, conoid tubulin fibers, conserved conoid-complex proteins, MyoH motor machinery, rare eukaryotic and common Apicomplexa taxonomic scope, Toxoplasma gondii as a canonical example, apical-scaffold and entry/exit functions, a conoid tubulin/MyoH function graph, and a grounding TODO for conoid protein cohorts.
• 2026-09-10T05:42:50Z claude · ADDRESS_QC — Changed the MyoH associated-machinery component essentiality from ESSENTIAL to UNKNOWN so it does not claim the motor is required to assemble the conoid; the Graindorge et al. 2016 evidence is retained for MyoH-dependent host-cell entry and exit.
• 2026-09-10T05:49:50Z claude · FIXED_EVIDENCE_SCOPE — Narrowed the Toxoplasma gondii canonical-example note to the Hu et al. 2002 conoid tubulin-polymer evidence so it no longer bundles Hu et al. 2006 apical-complex proteomics or Graindorge et al. 2016 MyoH entry/exit evidence under one canonical-example reference.
• 2026-10-11T19:53:37Z codex · ADDRESS_SAVED_REVIEW — Addressed #2250, #2251, #2252: Removed the heterogeneous whole-complex cohort from body constituents and the reside-in edge, retaining proteomic/conservation context in an appended discussion. Typed the conoid fiber polymer as a protein complex and the assembled fiber/protofilament graph nodes as structures; tubulin composition and scaffold relationships are unchanged. Replaced whole-phylum majority inference with Toxoplasma body occurrence, preserving the distinct reduced Plasmodium conoid-complex evidence as context without an absence claim.
• 2026-10-11T20:10:34Z codex · FIX_REMEDIATION_ANCHOR — Addressed #2255: made the new conoid scope discussion anchor reference the declared conoid_tubulin_fibers component, as required by the corpus anchor contract. No scientific claim, original discussion or earlier event changed.

Source: data/structures/cytoskeleton/conoid.yaml