basal body A-C linker

cellstructuremech:basal_body_a_c_linker · Cytoskeleton · Multiprotein complex · Proposed

A proteinaceous intertriplet linkage connecting the A-microtubule of one triplet to the C-microtubule of the neighboring triplet in the wall of a ciliary basal body. [DOI:10.1126/sciadv.ady3689]

Figure 1: Tetrahymena basal-body A-C linkers in situ and after isolation. A-C show segmented and denoised in-situ cryotomograms; F-G show isolated basal bodies with A-C linkers labeled. D is the isolation schematic and E is an SDS-PAGE gel, not microscopy. Scale bars: A, 200 nm; B-C and F-G, 100 nm. CRYO_ET · *Tetrahymena thermophila* (`NCBITaxon:5911`) · Bin Cai, Jingwei Xu, Erik H. Collet, Ellen Aarts, Leo Luo, Alexander Leitner, Takashi Ishikawa, Pedro Beltrao, Chad G. Pearson, Martin Pilhofer, et al.; CC BY, via PubMed Central · CC_BY_4_0 · source: PMC PMC12506977.1 F1 · `DOI:10.1126/sciadv.ady3689`

Synonyms: A-C linker

Part of: ciliary basal body (GO:0036064)

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

Components

Component	Type	Part of / acts on	Grounding	Genes	Essential	Role
WRAP73 family protein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	WRAP73, WDR8	UNKNOWN	A-link constituent modeled as a nine-bladed beta-propeller that contacts CEP135 and unassigned helical elements. It is retained in the proximal and transitional linker reconstructions in Tetrahymena. `DOI:10.1126/sciadv.ady3689` Results and Figure 5 identify the unusual beta-propeller by fitting an MS-derived AlphaFold model library into the map. Figure 6 retains WRAP73 in both forms; functional necessity is not established by this assignment.
CEP135 family protein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	CEP135, BLD10	UNKNOWN	A-link constituent whose modeled N-terminal dimer contacts WRAP73 and the central filament. A segment bridges A-microtubule protofilaments in the proximal form. The transitional form has an altered orientation and a less well resolved microtubule-contacting segment. `DOI:10.1126/sciadv.ady3689` Figure 5 and structural modeling support CEP135 placement and the approximately 325-360 contact segment. Methods explicitly cannot discriminate the two N-terminally similar variants in the density. GFP localization used induced constructs, not endogenous abundance.
TBC1D31 family protein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	TBC1D31, TBC1D31A, TBC1D31B, WDR67	UNKNOWN	Two TBC1D31-like proteins contribute to the proximal C-link and its staggered central helical filament. They connect the C-side interface to the A-link. These densities are not assigned in the transitional C-link, which has a different, unresolved composition. `DOI:10.1126/sciadv.ady3689` Figure 3 and Results assign the proximal C-link and central filament using density fitting, supported by GFP localization. The Results and Methods reverse the A/B accession aliases, so no exact paralogue accession pairing or whole-linker copy number is asserted.
POC1 family protein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	POC1	UNKNOWN	The C-terminal helix contributes to the proximal C-link alongside TBC1D31-like proteins; the N-terminal region associates with the neighboring B-C inner junction. The corresponding C-link density is not assigned in the transitional form. `DOI:10.1126/sciadv.ady3689` Figures 3-4 and the structural model connect POC1 to the proximal C-link and B-C junction. The verified POC1 accession is Q229Z6; the transposed accession in the article Methods is not copied into a protein example.

Canonical examples

NCBITaxon:5911 Tetrahymena thermophila — The study isolates basal bodies from strain SB715 and compares their architecture with in-situ cryotomograms. It calls these ciliary basal bodies centrioles for simplicity. GFP localization uses separately specified strains and constructs. [DOI:10.1126/sciadv.ady3689]

Functions

intertriplet microtubule linkage — Connects the A-microtubule of one basal-body triplet to the C-microtubule of its neighbor through a proteinaceous A-link/C-link assembly. Proximal and transitional forms achieve this connection with different C-side compositions.
- DOI:10.1126/sciadv.ady3689 Cryotomography and reconstructions in Figures 1-2 and 6 show the intertriplet bridge. This is a structural linkage function, not a measured force threshold or a demonstrated temporal assembly sequence.

Mechanism graphs

Structural contacts bridging adjacent basal-body triplets (FUNCTION)

A density-supported model of the proximal Tetrahymena A-C linker's physical connections to neighboring microtubules.

Subject	Predicate	Object	Evidence
WRAP73 family protein	coordinates	CEP135 family protein	`DOI:10.1126/sciadv.ady3689` Figure 5A-B and fitting of the predicted WRAP73-CEP135 complex into observed density support the contact arrangement.
CEP135 family protein	cross-bridges protofilaments of	A-microtubule of one basal-body triplet	`DOI:10.1126/sciadv.ady3689` Figure 5C; no claim that this contact alone induces the observed microtubule lattice compaction.
TBC1D31 family protein	contacts	CEP135 family protein	`DOI:10.1126/sciadv.ady3689` Figure 3B and Figure 5A; a collective family-level relationship avoids assigning a contradictory A/B accession alias.
POC1 family protein	contributes a C-terminal helix to	proximal C-link contact interface	`DOI:10.1126/sciadv.ady3689` Figure 3A and density fitting of the predicted subcomplex.
TBC1D31 family protein	contributes modeled binding domains to	proximal C-link contact interface	`DOI:10.1126/sciadv.ady3689` Figure 3A; domain names do not establish a Rab GTPase reaction.
proximal C-link contact interface	contacts	C-microtubule of the neighboring basal-body triplet	`DOI:10.1126/sciadv.ady3689` Results and Figure 3A support the subcomplex-level contact; it is not assigned exclusively to one protein.
CEP135 family protein	contributes the A-side attachment of	basal body A-C linker	`DOI:10.1126/sciadv.ady3689` Figures 3B and 5; the unidentified AHE network also contributes to attachment and is not omitted as if CEP135 acted alone.
proximal C-link contact interface	contributes the C-side attachment of	basal body A-C linker	`DOI:10.1126/sciadv.ady3689` Figure 3 and Results; transitional C-link protein identities are unresolved and are outside this graph.

Discussions

CURATION_TODO (RESOLVED): Distinguish the intertriplet A-C linker from the enclosing basal body and other basal-body modules. A named, imaged multi-protein linkage is a distinct structure, not a single protein or synonym of the whole basal body.
CURATION_TODO (OPEN): Resolve exact source-neutral groundings for WRAP73, CEP135, TBC1D31 and POC1 without using broader families or domains. All four named classes have structural evidence but their inspected integrated annotations do not establish exact family equivalence.
CURATION_TODO (OPEN): Identify the unassigned helical elements and transitional C-link proteins, and determine form-specific assembly requirements. The four-family list is incomplete and must not be interpreted as the universal composition of every A-C linker.
CURATION_TODO (OPEN): Reconcile TBC1D31 A/B aliases and CEP135 variant assignments before adding strain-paired protein examples. Article text and deposition mappings disagree at finer granularity than the supported family-level components.
CURATION_TODO (RESOLVED): Do not import all adjacent microtubule and junction material as A-C linker constituents. A deposited structural model can include connected modules outside the structure's curated composition boundary.

Datasets

Proximal A-C linker of Tetrahymena centriole, one repeating unit (PDB:9QZC) · RCSB_PDB · EXPERIMENTAL_STRUCTURE
Organism: Tetrahymena thermophila · Platform: cryo-electron microscopy with single-particle reconstruction and model fitting
Supports molecular assignments at the family level and preserves multiple unassigned protein chains. No global or local deposition copy number is promoted to whole-linker stoichiometry.
Official entry, all 15 polymer entities and assembly 1 inspected. The entry identifies NCBITaxon 5911 and links the primary DOI/PMID. Only metadata and links are retained, not coordinates. The CEP135 SIFTS assignment and article Methods differ; see the open discussion.

Evidence

DOI:10.1126/sciadv.ady3689 Cai et al. 2025. Official PMC12506977.1 metadata and checksum-verified JATS inspected. Main text, methods and figure captions read; Figures 1, 3, 5 and 6 inspected visually.
PMID:41061066 Bibliographic identity matches the official PMC metadata and PDB primary citation.
PDB:9QZC Official released model, exact primary citation, source organism, polymer entities and assembly inspected.

Curation history

2026-10-04T07:47:48Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-10-04T07:51:28Z codex · EXPANDED_RECORD — Added four evidence-backed component classes, Tetrahymena example, proximal structural-contact graph, PDB dataset and licensed cryotomography. Preserved compositional polymorphism, uncertain groundings and conflicting protein assignments without inferring temporal assembly or stoichiometry.
2026-10-11T10:36:33Z codex · ADDRESS_SAVED_REVIEW — Addressed #2206: corrected the A-C linker figure caption from raw to denoised in-situ tomography and documented the source DeepDeWedge processing, retaining image bytes and all biological claims.

Source: data/structures/cytoskeleton/basal_body_a_c_linker.yaml