CellStructureMech

basal body A-B inner junction

cellstructuremech:basal_body_a_b_inner_junction · Cytoskeleton · Multiprotein complex · Proposed

A protein network at the lumen-facing interface between the A- and B-tubules of a basal-body triplet microtubule, forming connections between the two tubules with region-specific composition. [DOI:10.1038/s44318-025-00392-6]

Representative density rendering of a focused 16-nm repeat of the wild-type Tetrahymena basal-body central-core A-B inner junction. This is a subtomogram average with adjacent tubule density, not a raw micrograph, whole basal body or individually labeled protein model. No scale bar is shown.
Representative density rendering of a focused 16-nm repeat of the wild-type Tetrahymena basal-body central-core A-B inner junction. This is a subtomogram average with adjacent tubule density, not a raw micrograph, whole basal body or individually labeled protein model. No scale bar is shown. CRYO_ET · Tetrahymena thermophila (NCBITaxon:5911) · Li S, Fernandez J, Ruehle M, Fabritius A, Pearson C, Agard DA, Winey M; EMDB depositor representative figure, without copyright restrictions. · PUBLIC_DOMAIN · source: EMDB EMD-46440 · DOI:10.1038/s44318-025-00392-6

Part of: ciliary basal body (GO:0036064)

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

Components

ComponentTypePart of / acts onGroundingGenesStoichiometryEssentialRole
POC1 family proteinProteinpart ofReviewed label only (reviewed name; no accession asserted)UNKNOWNBridges the A1/B10 inner junction in proximal and central-core basal-body regions. At the core it also provides an attachment toward the separate inner scaffold.
  • DOI:10.1038/s44318-025-00392-6 Results, Figures 2 and 4, and Figure EV4 place Poc1 at the junction. Poc1 deletion produces heterogeneous defects and replacement compositions, not uniform absence of every A-B junction; assembly essentiality is not assigned.
FAP52 family proteinProteinpart ofReviewed label only (reviewed name; no accession asserted)UNKNOWNCore-region microtubule inner protein contacting B9 and B10. A FAP52-like protein occupies a different, predominantly B9 position proximally; its precise paralog identity is unresolved.
  • DOI:10.1038/s44318-025-00392-6 Figures 2B, 4 and EV4 support the core assignment by model fitting. The proximal assignment is explicitly FAP52-like, not proven to be the same gene product as core FAP52.
FAP106 family proteinProteinpart ofReviewed label only (reviewed name; no accession asserted)UNKNOWNMicrotubule inner protein fitted at the proximal and core A-B inner junctions. Core models place it adjacent to FAP52; that proposed contact is not a binding assay.
  • DOI:10.1038/s44318-025-00392-6 Figures 2, 4 and EV4 identify FAP106 by structural fitting. Recruitment hierarchies from other species' axonemes are not direct basal-body assembly evidence.
IJ34 family proteinProteinpart ofReviewed label only (reviewed name; no accession asserted)UNKNOWNCore-region inner-junction protein whose main domain anchors to the A-tubule and whose C-terminal helix tethers FAP52 in the fitted structural model.
  • DOI:10.1038/s44318-025-00392-6 Figure 4F compares the core and axonemal models: different C-terminal-helix positions retain the FAP52 connection. This is a structural comparison, not a time-resolved conformational trajectory.
Cilia- and flagella-associated protein 45Proteinpart ofInterPro:IPR033253UNKNOWNCore-region junction-associated microtubule inner protein assigned within the 48-nm reconstruction by fitting an axonemal protein model.
  • DOI:10.1038/s44318-025-00392-6 Figures 4A and EV4A support the core assignment. Model source PDB 8G2Z maps CFAP45 to W7XCX2, whose exact InterPro family is IPR033253; this model crosscheck is not a strain-matched basal-body protein example.
Cilia- and flagella- associated protein 210Proteinpart ofInterPro:IPR039986UNKNOWNCore-region junction-associated microtubule inner protein assigned within the 48-nm reconstruction; its possible FAP52 contact remains model-derived.
  • DOI:10.1038/s44318-025-00392-6 Figures 4A and EV4A support the core assignment. Model source PDB 8G2Z maps CFAP210 to Q23EX8, annotated with the exact InterPro family IPR039986 despite a domain-based UniProt protein name. No direct binding assay is inferred.
alpha-helical inner-junction ladder proteinProteinpart ofReviewed label only (reviewed name; no accession asserted)UNKNOWNForms the alpha-helical ladder assigned to the proximal A-B inner junction, bridging protofilaments A13 and B10 in the structural model. This assignment is not transferred to the distinct core-region LRR density or the FAP52-like protein.
  • DOI:10.1126/sciadv.ady3689 Cai et al. 2025, Figure 4D-F and Results identify an I7LY02-containing array in the A-B junction, following the MS-guided predicted-model assignment of the corresponding B-C ladder. This supports source-assigned membership, not a knockout dependency, biochemical binding assay or assembly essentiality. RCSB 9QZC entity 8 independently maps the study's ladder model to I7LY02, but its A-C/B-C composite scope is not treated as an A-B-specific deposition.

Canonical examples

Functions

Mechanism graphs

Core-region A-B junction contacts (FUNCTION)

A bounded contact network from fitted Tetrahymena basal-body core models.

SubjectPredicateObjectEvidence
POC1 family proteincontactsbasal-body A-tubule
POC1 family proteincontactsbasal-body B-tubule
FAP52 family proteincontactsbasal-body B-tubule
IJ34 family proteinanchors tobasal-body A-tubule
IJ34 family proteintethersFAP52 family protein
  • DOI:10.1038/s44318-025-00392-6 Figure 4F and Results support the structural tether; flexibility is inferred from comparing structures, not observed real-time motion.

Discussions

Datasets

Evidence

Curation history

Source: data/structures/cytoskeleton/basal_body_a_b_inner_junction.yaml