BBS-9 (PTHB1 homolog) is a core subunit of the BBSome, the octameric ciliary coat complex (BBS-1, BBS-2, BBS-4, BBS-5, OSM-12/BBS-7, BBS-8/TTC-8, BBS-9) that couples intraflagellar transport (IFT) to the trafficking of membrane cargo at sensory cilia. It is built from an N-terminal Ξ²-propeller (WD40-like) together with platform and Ξ±-helical/hairpin regions characteristic of the PTHB1 family, and belongs β with BBS-2 and BBS-7 β to the Ξ²-propeller "core" of the complex. Like the COPI, COPII and clathrin coats it structurally resembles, the BBSome assembles IFT particles at the ciliary base, binds the anterograde IFT particle as a cargo, and reaches the ciliary tip where it regulates IFT turnaround and recycling. In C. elegans, BBS-9 is expressed in ciliated sensory neurons, undergoes IFT along the axoneme, and is required for proper BBSome assembly and its ciliary localization: a bbs-9 nonsense allele uncouples the IFT-A and IFT-B subcomplexes during anterograde transport, the canonical loss-of-BBSome phenotype, and bbs-9 mutants have defective cilia with mislocalized, poorly transported IFT proteins. Loss of bbs-9, like loss of other BBSome subunits, causes cilium-dependent sensory and developmental defects, including reduced body size, developmental delay, and failure to detect and avoid nitric oxide and NO-producing Pseudomonas aeruginosa.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0016020 membrane | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: High-level "membrane" localization propagated by phylogenetic inference. BBS-9 is a peripheral coat scaffold that associates with the ciliary membrane at the ciliary base/tip as part of the BBSome, but "membrane" with an is_active_in qualifier is uninformative for a structural subunit and far less specific than the ciliary basal-body and BBSome annotations. Reason: Overly general and derived: the informative, experimentally supported localizations for worm BBS-9 are the ciliary basal body/base and the BBSome; a bare "membrane" term (and the is_active_in qualifier, which implies a molecular function occurring at the membrane) adds no specific biological information and is flagged as over-annotation. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: MGI:MGI:2442833 Β· Bbs9 UniProtKB:Q3SYG4 Β· BBS9 (human) |
| GO:0034464 BBSome | IBA GO_REF:0000033 | ACCEPT | Summary: BBS-9 is a bona fide subunit of the BBSome, the octameric complex (BBS-1, BBS-2, BBS-4, BBS-5, OSM-12/BBS-7, BBS-8/TTC-8, BBS-9). This phylogenetic (IBA) assignment matches the direct C. elegans BiFC evidence that BBS-1 and BBS-9 coexist in the same complex and the human BBSome architecture in which BBS1/7/9 lie together. Reason: Complex membership is the defining, core cellular-component property of bbs-9 and is supported by both phylogenetic inference and direct C. elegans experiments. Supporting Evidence: PMID:22922713 consistent with the prediction that mammalian BBS1, 7, and 9 locate closely to each other in the BBSome |
| GO:0060271 cilium assembly | IBA GO_REF:0000033 | ACCEPT | Summary: BBS-9 contributes to cilium assembly as part of the BBSome, which assembles IFT particles required for ciliogenesis. In C. elegans bbs-9 mutants have defective cilia with mislocalized and poorly transported IFT proteins. Reason: Well supported by phylogenetic inference and by direct C. elegans genetics; a core biological-process annotation for a BBSome subunit. Supporting Evidence: PMID:22922713 the in vivo function for the BBSome is to regulate the assembly of the IFT particles at the ciliary base |
| GO:0034464 BBSome | IEA GO_REF:0000002 | ACCEPT | Summary: Electronic InterPro-to-GO mapping (IPR026511, PTHB1) assigning BBSome membership. This duplicates the IBA and NAS BBSome annotations and is consistent with the direct experimental complex-membership evidence. Reason: Correct BBSome membership from the PTHB1 InterPro signature; redundant with the higher-evidence NAS/IBA annotations but not wrong. Core cellular-component. Supporting Evidence: PMID:22922713 fluorescence complementation can be observed in BBS-1 |
| GO:0005929 cilium | NAS PMID:22922713 The BBSome controls IFT assembly and turnaround in cilia. | KEEP AS NON CORE | Summary: BBS-9 localizes to cilia as a BBSome subunit that undergoes IFT along the ciliary axoneme; when the BBSome is uncoupled from moving IFT, BBS-9 shows only dim ciliary staining and accumulates at the base. A correct but general localization β the ciliary basal body/base terms are more specific. Reason: Accurate general localization supported by the referenced work, but non-core relative to the more specific ciliary basal body / ciliary base terms which are the core CC annotations; retained as a valid non-core localization. Supporting Evidence: PMID:22922713 only showed very dim ciliary staining when compared to |
| GO:0034464 BBSome | NAS PMID:22922713 The BBSome controls IFT assembly and turnaround in cilia. | ACCEPT | Summary: Author-stated (NAS, ComplexPortal) assignment of BBSome membership, duplicating the IBA and IEA annotations. Directly supported by the C. elegans BiFC evidence that BBS-1 and BBS-9 are in the same complex. Reason: Correct and consistent with the other BBSome annotations and with direct worm experiments; the core cellular-component annotation for bbs-9. Supporting Evidence: PMID:22922713 indicative of the coexistence of these three BBS proteins in the same complex |
| GO:0060271 cilium assembly | NAS PMID:22922713 The BBSome controls IFT assembly and turnaround in cilia. | ACCEPT | Summary: Author-stated (NAS) cilium-assembly role, duplicating the IBA annotation. The BBSome assembles IFT particles required for ciliogenesis, and bbs-9 mutants show defective cilia. Reason: Correct and consistent with the IBA annotation and with C. elegans genetics; retained as complementary evidence for the same core biological-process role. Supporting Evidence: PMID:22922713 the in vivo function for the BBSome is to regulate the assembly of the IFT particles at the ciliary base |
| GO:0036064 ciliary basal body | IDA PMID:22922713 The BBSome controls IFT assembly and turnaround in cilia. | ACCEPT | Summary: Direct experimental (IDA) localization of BBS-9 to the ciliary basal body/base in C. elegans, consistent with strong BBSome accumulation around the ciliary base when the complex is uncoupled from moving IFT. This is the site where the BBSome assembles IFT particles. Reason: Experimental localization; the strongest evidence class for the basal-body assignment and the core cellular-component annotation for worm BBS-9. Supporting Evidence: PMID:22922713 all BBS proteins examined strongly accumulated around the ciliary base |
| GO:0097546 ciliary base | IDA PMID:22922713 The BBSome controls IFT assembly and turnaround in cilia. | NEW | Summary: BBS-9, like the other BBSome subunits, concentrates at the ciliary base where the BBSome assembles IFT particles; when the BBSome is uncoupled from moving IFT the proteins strongly accumulate there. This is a more precise localization than the general 'cilium' term and complements the ciliary basal body annotation. Reason: Ciliary base is the experimentally supported site of BBSome-mediated IFT assembly in C. elegans and is included as a location in core_functions; added here as a specific cellular-component annotation. Supporting Evidence: PMID:22922713 all BBS proteins examined strongly accumulated around the ciliary base |
| GO:0042073 intraciliary transport | IMP PMID:22922713 The BBSome controls IFT assembly and turnaround in cilia. | NEW | Summary: BBS-9, as a BBSome subunit, itself undergoes IFT movement along the ciliary axoneme and is required for normal intraflagellar transport; a bbs-9 nonsense allele uncouples IFT-A from IFT-B during anterograde transport and the BBSome loses IFT movement when detached from IFT particles. Reason: Intraciliary transport is a core biological process for the BBSome, captured in core_functions; added here as a specific process annotation supported by BBS-9 IFT movement and the IFT-uncoupling phenotype of the bbs-9 allele. Supporting Evidence: PMID:22922713 encodes BBS-9 with a nonsense mutation at Q171 site PMID:22922713 all BBS proteins completely lost IFT movement |
| GO:0061512 protein localization to cilium | IBA GO_REF:0000033 | NEW | Summary: As a BBSome subunit, BBS-9 is required for correct trafficking of membrane and signaling proteins to/from cilia; the BBSome couples ciliary cargo to IFT and, when disrupted, ciliary receptors mislocalize. Supported by phylogenetic inference and by the conserved BBSome cargo-trafficking role. Reason: Protein localization to cilium is a core BBSome-mediated process captured in core_functions; added here as a specific biological-process annotation, consistent with the phylogenetically inferred BBSome function. Supporting Evidence: PMID:22922713 shares the common structural features with COPI, COPII, and clathrin coats, and can directly recognize IFT cargos |
| GO:0030674 protein-macromolecule adaptor activity | ISS file:worm/bbs-9/bbs-9-deep-research-falcon.md | NEW | Summary: BBS-9 acts as a protein-macromolecule adaptor/scaffold within the coat-like BBSome rather than as an enzyme: structurally it is the central hub that directly contacts more subunits than any other component (its GAE domain heterodimerizes with BBS1 and its C-terminal coiled-coil pairs with BBS2 to form the neck). This is far more informative than 'protein binding' and is the best available molecular-function description for a BBSome coat subunit. Reason: Adaptor/scaffold activity is the most defensible molecular function for a BBSome structural subunit and is preferable to uninformative protein binding; included in core_functions. No experimental MF has been measured for BBS-9 itself and no GO term specifically expresses the BBSome coat/cargo-adaptor role - see knowledge_gaps. Supporting Evidence: PMID:22922713 shares the common structural features with COPI, COPII, and clathrin coats, and can directly recognize IFT cargos |
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Download this section (compressed HTML)Q: Does the BBS-9 Ξ²-propeller directly contact a specific ciliary membrane cargo or a specific neighboring BBSome subunit interface, and is that contact required for IFT-A/IFT-B coupling?
Q: Is there a subunit-specific role for BBS-9 in nucleating BBSome assembly (as part of the BBS-2/7/9 core) that is separable from bulk IFT-particle assembly?
Experiment: Cryo-EM/structural analysis of the C. elegans (or reconstituted) BBSome with BBS-9 to map the BBS-9 Ξ²-propeller interfaces, combined with proximity-dependent biotinylation (TurboID) of BBS-9 at the ciliary base to identify cargo and neighbors.
Hypothesis: The BBS-9 Ξ²-propeller forms defined intra-complex and cargo contacts that couple the BBSome coat to IFT particles.
Type: structural_biology
Experiment: Structure-guided separation-of-function bbs-9 alleles that perturb individual interfaces while preserving overall folding, scored for BBSome assembly, IFT-A/IFT-B coupling, base-versus-tip IFT dynamics, and ciliary receptor trafficking.
Hypothesis: Specific BBS-9 interfaces are required for distinct steps (assembly at the base versus turnaround at the tip), separable from whole-complex loss.
Type: genetics
What is not known β curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: There is no GO molecular-function term that expresses the role of a BBSome coat/scaffold subunit, and BBS-9 has no experimentally measured biochemical activity of its own. Unlike the peripheral subunit BBS-4, worm BBS-9 has no molecular-function annotation of any kind in GOA (its only MF-adjacent term is the uninformative "membrane"), so the specific intra-BBSome contacts made by the BBS-9 Ξ²-propeller and the cargo(es) it helps recognize are undefined.
OPEN ONTOLOGYBIOLOGY MF_DARK
What is known: BBS-9 is an established BBSome subunit built from a WD40-like Ξ²-propeller plus PTHB1 platform/hairpin domains, and lies close to BBS-1 and BBS-7 in the complex; the BBSome is explicitly coat-like (shares structural features with COPI, COPII and clathrin) and can directly recognize IFT cargo. What is missing is a molecular-function term (and the direct cargo/partner identity) for the coat subunit itself rather than the complex-level process.
Significance: BBSome subunits illustrate the structural-subunit ontology gap: their function is "be part of the coat", which the GO molecular-function aspect cannot currently express, so BBS-9 reads as MF-dark despite a well-defined cellular role central to Bardet-Biedl syndrome.
What would resolve it: Ontology development of a BBSome coat/cargo-adaptor molecular-function term (analogous to a vesicle-coat adaptor), plus structural and proximity/affinity proteomics to define the intra-complex contacts and membrane cargo contacted by the BBS-9 Ξ²-propeller.
Provenance (the field's own admissions):
Proposed term (ontology gap):
Gap: Whether BBS-9, as a Ξ²-propeller "core" (BBS-2/BBS-7/BBS-9) subunit, plays a distinct nucleating/assembly role separable from the peripheral subunits, and what its individual contribution is to IFT-particle assembly at the ciliary base versus IFT turnaround at the tip, have not been resolved experimentally in C. elegans.
OPEN BIOLOGY RESIDUAL_SUBGAP
What is known: A bbs-9 nonsense allele (Q171) uncouples IFT-A from IFT-B during anterograde transport, like other bbs-null mutants, and BBS-9 itself undergoes IFT and accumulates at the ciliary base when the BBSome is uncoupled from moving IFT. What remains unknown is the subunit-specific step BBS-9 mediates within complex assembly and IFT coupling, as distinct from the whole-complex loss-of-function phenotype.
Significance: Dissecting subunit-specific roles is needed to understand why individual BBS genes give overlapping but not identical Bardet-Biedl syndrome phenotypes, and to model the stepwise assembly of the ciliary coat.
What would resolve it: Separation-of-function bbs-9 alleles and structure-guided mutations that perturb specific intra-BBSome interfaces, scored for BBSome assembly, IFT-A/IFT-B coupling, base-versus-tip IFT dynamics, and cargo trafficking.
Provenance (the field's own admissions):
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