radial spoke

GO:0001534 · Cytoskeleton · Multiprotein complex · Proposed

A ciliary and flagellar axonemal protein complex with a stalk attached to each outer-doublet A-tubule and a head that projects toward the central-pair microtubule sheath. [GO:0001534]

Part of: axoneme (GO:0005930)

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

Components

Component	Type	Part of / acts on	Grounding	Essential	Role
radial spoke head	Protein complex	part of	`GO:0001535`	UNKNOWN	Globular head subcomplex that projects from the radial spoke toward the axonemal central pair. `GO:0001535` GO identifies the radial spoke head as the portion of the radial spoke orthogonal to the stalk that projects toward the central pair. `DOI:10.1242/jcs.245233` Poghosyan et al. 2020 refined the Chlamydomonas radial-spoke architecture and assigned protein densities to the head region.
radial spoke neck	Protein complex	part of	`GO:0120343`	UNKNOWN	Connector subcomplex between the radial-spoke stalk and head. `GO:0120343` GO identifies the radial spoke neck as the complex that connects the spoke stalk to the spoke head. `DOI:10.1242/jcs.245233` Poghosyan et al. 2020 model the radial-spoke neck as a distinct Chlamydomonas radial-spoke region.
radial spoke stalk	Protein complex	part of	`GO:0001536`	UNKNOWN	Elongated subcomplex that connects the A-tubule-binding radial-spoke base to the neck. `GO:0001536` GO identifies the radial spoke stalk as the elongated radial-spoke portion between the A-tubule-binding base and the neck. `DOI:10.1242/jcs.245233` Poghosyan et al. 2020 assigned Chlamydomonas radial-spoke proteins to the stalk region.

Taxonomic distribution

NCBITaxon:3055 Chlamydomonas reinhardtii — COMMON: Chlamydomonas flagellar axonemes carry radial spokes that have been resolved by cryoelectron tomography. [DOI:10.1126/science.1128618]

Canonical examples

NCBITaxon:3055 Chlamydomonas reinhardtii — Green-algal model whose flagellar radial spokes have been structurally analyzed by cryoelectron tomography and cryo-EM. [DOI:10.1242/jcs.245233]

Functions

regulation of cilium movement GO:0003352 — Radial spokes form part of the axonemal transducer system that links outer doublets to the central pair and helps regulate dynein-driven ciliary and flagellar beating.
- DOI:10.1242/jcs.245233 Poghosyan et al. 2020 describe the Chlamydomonas radial spoke as a complex in the ciliary motility transducer apparatus.

Mechanism graphs

Head, neck and stalk organize the radial spoke (FUNCTION)

In Chlamydomonas flagella, the radial-spoke base binds an outer-doublet A-tubule, the stalk connects the base to the neck, and the neck connects to the head, which projects toward the central pair to help regulate axonemal beating.

Subject	Predicate	Object	Evidence
radial spoke head	is part of	radial spoke	`GO:0001535` GO places the radial spoke head as part of the radial spoke.
radial spoke neck	connects to	radial spoke head	`GO:0120343` GO defines the radial spoke neck by its connection between the stalk and head.
radial spoke neck	connects to	radial spoke stalk	`GO:0120343` GO defines the radial spoke neck by its connection between the stalk and head.
radial spoke stalk	connects to	radial spoke base	`GO:0001536` GO defines the stalk as the elongated portion between the A-tubule-binding base and the neck; the base is not included in this exact stalk grounding.
radial spoke base	binds to	outer doublet microtubule	`GO:0001536` The stalk definition identifies the base as the portion that binds the outer-doublet A-tubule.
radial spoke head	projects toward	axonemal central pair	`GO:0001535` GO defines the radial spoke head as the radial-spoke portion that projects toward the central pair. `DOI:10.1126/science.1128618` Nicastro et al. 2006 visualized radial spokes in Chlamydomonas 9+2 axonemes.
radial spoke	participates in	regulation of cilium movement	`DOI:10.1242/jcs.245233` Poghosyan et al. 2020 frame the radial spoke as a complex in the ciliary motility transducer apparatus.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral groundings and copy numbers for the head, neck and stalk RSP protein families of the Chlamydomonas radial spoke. GO exactly identifies the radial-spoke head, neck and stalk subcomplexes, but this pass did not verify exact source-neutral InterPro, Pfam or other accessions for the individual RSP protein families.

Evidence

GO:0001534 Gene Ontology cellular-component term for the radial spoke.
GO:0001535 Gene Ontology cellular-component term for the radial spoke head.
GO:0120343 Gene Ontology cellular-component term for the radial spoke neck.
GO:0001536 Gene Ontology cellular-component term for the radial spoke stalk.
GO:0005930 Gene Ontology places the radial spoke within the axoneme.
DOI:10.1126/science.1128618 Nicastro et al. 2006, 'The molecular architecture of axonemes revealed by cryoelectron tomography', Science.
DOI:10.1242/jcs.245233 Poghosyan et al. 2020, 'The structure and symmetry of the radial spoke protein complex in Chlamydomonas flagella', Journal of Cell Science.

Curation history

2026-09-23T09:33:39Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-23T09:35:54Z codex · EXPANDED_RECORD — Added axoneme parthood, GO-grounded head, neck and stalk subcomplexes, Chlamydomonas scope, cilium-movement regulation function, GO and DOI evidence, a nonmechanistic radial-spoke function graph, and an RSP component-grounding TODO.
2026-09-23T09:36:37Z codex · REFINE_RADIAL_SPOKE_MODEL — Kept head, neck and stalk as GO-grounded components rather than child records, narrowed the Chlamydomonas distribution note to cryoelectron tomography evidence, and clarified the regulation graph predicate.
2026-09-23T09:55:27Z codex · ADDRESSED_REVIEW — Resolved PR #1377 review issues #1378 and #1379 by changing the radial-spoke-head edge to static parthood and adding the missing neck-to-stalk edge.
2026-10-11T11:22:03Z codex · ADDRESS_SAVED_REVIEW — Addressed #2208: separated the A-tubule-binding base from the GO:0001536 stalk in the component role and whole-spoke topology graph.

Source: data/structures/cytoskeleton/radial_spoke.yaml