axonemal central pair projection

GO:1990718 · Cytoskeleton · Multiprotein complex · Proposed

A projection structure that extends from the C1 or C2 singlet microtubule of the 9+2 axonemal central apparatus. [GO:1990718]

Part of: axonemal central apparatus (GO:1990716)

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
axonemal central-pair projection proteins	Protein	part of	Reviewed label only (reviewed name; no accession asserted)			UNKNOWN	Protein constituents of projection structures that extend from the axonemal C1 and C2 central-pair microtubules. `GO:1990718` GO identifies axonemal central pair projections as projection structures off the central pair of single microtubules. `DOI:10.1002/cm.21094` Carbajal-Gonzalez et al. 2013 resolved C1 and C2 central-pair projections in Chlamydomonas and Strongylocentrotus by cryo-ET and subtomogram averaging.

NCBITaxon:3055 Chlamydomonas reinhardtii — COMMON: Chlamydomonas flagellar central pair complexes contain C1 and C2 projections that extend from the central singlet microtubules. [DOI:10.1002/cm.21094]

NCBITaxon:3055 Chlamydomonas reinhardtii — Green-algal model whose central pair projections were resolved as asymmetric C1 and C2 densities by cryoelectron tomography. [DOI:10.1002/cm.21094]

central-pair microtubule projection — Axonemal central pair projections extend from the C1 or C2 singlet microtubule toward the surrounding radial-spoke and outer-doublet ring.
- GO:1990718 GO defines axonemal central pair projections as projections off the central pair of single microtubules.
- DOI:10.1002/cm.21094 Carbajal-Gonzalez et al. 2013 modeled Chlamydomonas C1 and C2 central-pair projections extending from the central microtubules toward radial spokes and outer doublets.

Axonemal central-pair projection proteins form C1 and C2 projection structures within the Chlamydomonas central pair complex.

Subject	Predicate	Object	Evidence
axonemal central-pair projection proteins	form	axonemal central pair projection	`DOI:10.1002/cm.21094` Carbajal-Gonzalez et al. 2013 resolved a connected projection network on the Chlamydomonas C1 and C2 microtubules.
axonemal central pair projection	projects from	axonemal central pair	`GO:1990718` GO defines axonemal central pair projections as projections off the central pair of single microtubules.
axonemal central pair projection	projects toward	radial spoke	`DOI:10.1002/cm.21094` Carbajal-Gonzalez et al. 2013 describe central pair projections that extend toward radial spokes and doublet microtubules.
axonemal central pair projection	is part of	axonemal central apparatus	`GO:1990718` GO places the axonemal central pair projection within the axonemal central apparatus.

CURATION_TODO (OPEN): Resolve exact source-neutral groundings, record boundaries and copy numbers for C1a/C1b/C1c/C1d/C1e/C1f and C2a/C2b/C2c/C2d/C2e axonemal central pair projection subcomplexes. Carbajal-Gonzalez et al. 2013 resolved named C1 and C2 projection densities, but this pass only curates the broad GO:1990718 projection class and leaves exact named projection subcomplexes and their protein-family groundings unresolved.

GO:1990718 Gene Ontology cellular-component term for the axonemal central pair projection.
GO:1990716 Gene Ontology places axonemal central pair projections within the axonemal central apparatus.
DOI:10.1002/cm.21094 Carbajal-Gonzalez et al. 2013, 'Conserved structural motifs in the central pair complex of eukaryotic flagella', Cytoskeleton.

2026-09-23T15:11:25Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-23T15:12:47Z codex · EXPANDED_RECORD — Added central-apparatus parthood, a reviewed-label-only central-pair projection protein component, Chlamydomonas scope, GO and DOI evidence, a nonmechanistic projection architecture graph, and a named-projection subcomplex TODO.
2026-09-23T15:15:02Z codex · FIX_CENTRAL_PAIR_PROJECTION_TODO — Added C2e to the named central-pair projection subcomplexes left for later curation.
2026-09-23T15:18:40Z codex · SINGULARIZE_GRAPH_TITLE — Singularized the central-pair projection graph title to match GO:1990718.