axonemal microtubule doublet inner sheath

GO:0160110 · Cytoskeleton · Multiprotein complex · Proposed

A structural network of microtubule inner proteins located inside the lumens of the A and B tubules of the axonemal microtubule doublet that helps stabilize the doublet microtubule. [GO:0160110]

Part of: axonemal doublet microtubule (GO:0097545)

Has part: axonemal A tubule inner sheath (GO:0160111); axonemal B tubule inner sheath (GO:0160112)

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

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
inner-sheath microtubule inner proteins	Protein	part of	Reviewed label only (reviewed name; no accession asserted)			UNKNOWN	Globular and filamentous luminal MIPs that build the axonemal doublet inner sheath along A- and B-tubule protofilaments. `GO:0160110` GO defines the axonemal microtubule doublet inner sheath as a structural network of MIPs in the A- and B-tubule lumens. `DOI:10.1038/ncomms15035` Ichikawa et al. 2017 resolved globular and filamentous MIP densities inside Tetrahymena axonemal doublet microtubules. `DOI:10.1016/j.cell.2019.09.030` Ma et al. 2019 resolved interconnected MIP networks in native Chlamydomonas axonemal doublets.

Taxonomic distribution

NCBITaxon:3055 Chlamydomonas reinhardtii — COMMON: Chlamydomonas axonemal doublets contain luminal MIP networks in their A and B tubules. [DOI:10.1016/j.cell.2019.09.030]

Canonical examples

NCBITaxon:3055 Chlamydomonas reinhardtii — Green-algal model whose native axonemal doublet microtubules have been structurally resolved with luminal microtubule inner proteins. [DOI:10.1016/j.cell.2019.09.030]

Functions

doublet microtubule stabilization — Inner-sheath MIPs bind the luminal surfaces of axonemal doublets and help stabilize A- and B-tubule protofilament lattices against bending stress.
- GO:0160110 GO defines the inner sheath as an A/B-tubule MIP network that helps stabilize the doublet microtubule.
- DOI:10.1038/s41467-019-09051-x Owa et al. 2019 found that Chlamydomonas FAP45 and FAP52 are B-tubule luminal MIPs whose loss destabilizes axonemal doublet B tubules.

Mechanism graphs

A- and B-tubule MIPs form the inner sheath (FUNCTION)

Luminal microtubule inner proteins form A- and B-tubule inner sheaths that are part of the axonemal doublet and help stabilize the doublet lattice.

Subject	Predicate	Object	Evidence
inner-sheath microtubule inner proteins	form	axonemal microtubule doublet inner sheath	`GO:0160110` GO defines the inner sheath as a structural network of MIPs.
axonemal A tubule inner sheath	is part of	axonemal microtubule doublet inner sheath	`GO:0160111` GO places the axonemal A tubule inner sheath within the axonemal microtubule doublet inner sheath.
axonemal B tubule inner sheath	is part of	axonemal microtubule doublet inner sheath	`GO:0160112` GO places the axonemal B tubule inner sheath within the axonemal microtubule doublet inner sheath.
axonemal microtubule doublet inner sheath	stabilizes	axonemal doublet microtubule	`GO:0160110` GO defines the inner sheath as helping to stabilize the doublet microtubule. `DOI:10.1038/s41467-019-09051-x` Owa et al. 2019 identified Chlamydomonas B-tubule MIPs that bind inside doublet microtubules and stabilize the B-tubule wall.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral groundings, memberships, and copy numbers for A- and B-tubule inner-sheath MIP families. GO exactly identifies the inner-sheath network, but this pass did not verify InterPro, Pfam or other source-neutral family groundings for its individual globular and filamentous MIP constituents.
CURATION_TODO (RESOLVED): Decide whether GO:0160112 should become a separate B-tubule inner-sheath child record after its conserved MIP set is reviewed. GO exactly identifies the A- and B-tubule inner sheaths, but the present GO:0160110 record keeps them as child GO terms while their component boundaries and taxon-general MIP family identities remain unresolved. Historical reassessment at git d13891318477: GO exactly identifies the B-tubule inner sheath, but the present GO:0160110 record keeps it as a child GO term while its component boundaries and taxon-general MIP family identities remain unresolved.

Evidence

GO:0160110 Gene Ontology cellular-component term for the axonemal microtubule doublet inner sheath.
GO:0160111 Gene Ontology cellular-component term for the axonemal A tubule inner sheath.
GO:0160112 Gene Ontology cellular-component term for the axonemal B tubule inner sheath.
GO:0097545 GO places the axonemal microtubule doublet inner sheath within the axonemal doublet microtubule.
DOI:10.1038/ncomms15035 Ichikawa et al. 2017, 'Subnanometre-resolution structure of the doublet microtubule reveals new classes of microtubule-associated proteins', Nature Communications.
DOI:10.1038/s41467-019-09051-x Owa et al. 2019, 'Inner lumen proteins stabilize doublet microtubules in cilia and flagella', Nature Communications.
DOI:10.1016/j.cell.2019.09.030 Ma et al. 2019, 'Structure of the Decorated Ciliary Doublet Microtubule', Cell.

Curation history

2026-09-23T12:16:07Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-23T12:17:31Z codex · EXPANDED_RECORD — Added doublet parthood, A- and B-tubule inner-sheath child GO terms, a reviewed-label-only MIP component, Chlamydomonas scope, stabilization function, GO and DOI evidence, a nonmechanistic inner-sheath graph, and MIP/child-boundary TODOs.
2026-09-23T12:29:50Z codex · ADDRESSED_REVIEW — Resolved PR #1393 review issue #1395 by replacing unsupported one-half descriptions on A- and B-tubule inner-sheath graph edges.
2026-09-23T18:02:19Z codex · ADD_A_TUBULE_INNER_SHEATH_CHILD — Linked GO:0160111 to its own child record and narrowed the remaining inner-sheath child-record TODO to GO:0160112.
2026-09-23T18:30:46Z codex · ADD_B_TUBULE_INNER_SHEATH_CHILD — Linked GO:0160112 to its own child record and resolved the remaining inner-sheath child-record TODO.
2026-09-23T18:39:04Z codex · ADDRESSED_REVIEW — Resolved PR #1416 issue #1417 by clarifying that the GO:0160112 child split leaves exact B-tubule MIP-family curation open on the child record.
2026-10-11T08:56:27Z codex · ADDRESS_SAVED_REVIEW — Addressed #2199: restored original and intermediate discussion rationales with revision context; preserved the current prompt, task lifecycle, original dates, scientific claims and child-record boundaries.

Source: data/structures/cytoskeleton/axonemal_microtubule_doublet_inner_sheath.yaml