basal body C-tubule hook

cellstructuremech:basal_body_c_tubule_hook · Cytoskeleton · Other · Proposed

A hook-shaped proteinaceous linker at the external B-C interface of a basal-body microtubule triplet. In the distal half of isolated Chlamydomonas reinhardtii basal bodies, hook densities occupy the C1 position, extend across the outer surfaces of C2-C4, and recur along the triplet axis. [DOI:10.1038/emboj.2011.460]

Image (not hosted — OTHER): PMC3273388.1:f4

Regional triplet density reconstructions. Panel B shows yellow exterior hooks in the blue distal-half reconstruction beside the green proximal comparison. Panel C instead shows separate luminal filaments. Panel A has a 10-nm scale bar. The displayed segment length is not the biological length of a hook array. CRYO_ET · Chlamydomonas reinhardtii (NCBITaxon:3055) · Sam Li, Jose-Jesus Fernandez, Wallace F Marshall and David A Agard; Figure 4, The EMBO Journal (2012), DOI:10.1038/emboj.2011.460. Copyright 2012 European Molecular Biology Organization; CC BY-NC-ND 3.0 Unported. · OTHER · source: PMC PMC3273388.1:f4 · DOI:10.1038/emboj.2011.460

Part of: ciliary basal body (GO:0036064)

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

Canonical examples

NCBITaxon:3055 Chlamydomonas reinhardtii — Distal-half triplet reconstructions from isolated basal bodies; Figure 4B distinguishes the exterior hook from the separate luminal C-tubule filaments in Figure 4C. This is a species example, not a claim of occurrence in every strain or every basal-body region. [DOI:10.1038/emboj.2011.460]

Functions

external B-C tubule linkage — In the characterized Chlamydomonas distal region, the hook bridges the B4/C1 interface and extends across the outer C2-C4 surfaces. This is a structural connection, not a demonstrated hook-specific requirement for assembly, force resistance or motility.
- DOI:10.1038/emboj.2011.460 Regional cryo-electron tomography averages and Figure 4B resolve the exterior linker. B4 contact is described in the longitudinal-variation Discussion; molecular identity and assembly chronology remain interpretive.

Physical properties

OTHER: 8 UO:0000018 (Longitudinal spacing of the hook-associated density at C1 in the distal-half Chlamydomonas reinhardtii basal-body triplet subtomogram average; not hook length, width or a universal repeat.) [DOI:10.1038/emboj.2011.460]

Discussions

CURATION_TODO (RESOLVED): Separate the external C-tubule hook from other triplet linkers. This is an imaged named subassembly, not a gene product. Classification reassessment on 2026-10-11: the previous GO:0005856 is-a parent conflated a subassembly with its containing framework. GO:0005575 is retained conservatively because the inspected density does not establish a protein-complex or polymeric-fiber classification; morphology and basal-body parthood are unchanged.
CURATION_TODO (OPEN): Identify the protein constituents of the distal C-tubule hook. Density shape and estimated mass do not identify gene products.
CURATION_TODO (RESOLVED): Keep assembly hypotheses separate from direct hook composition. Regional correlation is not molecular or causal identification.
CURATION_TODO (OPEN): Resolve the relationship between the hook and the C-stretch. A similar position alone cannot establish homology or synonymy.
CURATION_TODO (RESOLVED): Distinguish a biological repeat from reconstruction metadata. An imaging window and map resolution are not structure size.

Datasets

Chlamydomonas basal-body triplet reconstruction (EMDB:EMD-5252) · OTHER · STRUCTURAL_IMAGING
Organism: Chlamydomonas reinhardtii · Platform: cryo-electron tomography and subtomogram averaging
Released native EMDB metadata links taxon 3055, strain cc3491 and PMID:22157822 with the exact primary DOI. The species example does not transfer this archive-only strain label into an assertion about a separately deposited hook map. Whole-triplet mass, component counts and map resolution are not hook composition or dimensions; no map volume is hosted.

Evidence

DOI:10.1038/emboj.2011.460 Li et al. 2012, PMID:22157822. Official PMC3273388.1 JATS and Figure 4 media checksums verified; non-tubulin and longitudinal Results, longitudinal Discussion, Methods and figure captions read. The morphology is directly observed, but the proposed assembly sequence and protein assignments are not established by those static reconstructions. No verbatim snippet is asserted.
DOI:10.15252/embj.2020106249 Nazarov et al. 2020, PMID:32954505. Official PMC7667878.1 JATS and Figure 4 media checksums verified; comparative peripheral architecture Results and organism/purification Methods inspected. Figure 4I supports a Teranympha mirabilis C-stretch lead, not an established cross-species synonym or example of this hook.

Curation history

2026-10-04T11:30:32Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-10-04T11:32:38Z codex · CURATED_RECORD — Added bounded Chlamydomonas morphology, axial repeat, structural linkage, whole-triplet dataset and link-only Figure 4 provenance. Kept molecular composition, causal mechanism and C-stretch equivalence unresolved.
2026-10-04T11:37:25Z codex · CORRECTED_EVIDENCE_SCOPE — Corrected the C-stretch comparison genus to Teranympha mirabilis after reinspection of Nazarov et al. Figure 4 and full-name Results. Chlamydomonas-only hook scope and unresolved homology are unchanged.
2026-10-11T09:48:32Z codex · ADDRESS_SAVED_REVIEW — Addressed #2203: Replaced the unsupported cytoskeleton is-a parent with conservative cellular-component classification, retained basal-body parthood and unknown molecular identity, and corrected current classification notes without rewriting original discussion provenance.

Source: data/structures/cytoskeleton/basal_body_c_tubule_hook.yaml