BBS12 is a divergent type II chaperonin-like protein that participates in BBSome assembly. It associates with MKKS/BBS6, BBS10, BBS7 and CCT/TRiC proteins in machinery that stabilizes assembly intermediates and supports incorporation of BBSome subunits. BBS12 is released as assembly proceeds. The mature BBSome contains BBS1, BBS2, BBS4, BBS5, BBS7, TTC8/BBS8, BBS9 and BBIP1 and controls membrane-protein trafficking at cilia. BBS12 has a cytoplasmic pool and localizes to ciliary basal bodies in human cell models. Biallelic pathogenic variants cause Bardet-Biedl syndrome type 12, with variable retinal degeneration, obesity, polydactyly, renal abnormalities and hypogenitalism.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0045494 photoreceptor cell maintenance | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: The PAINT annotation places BBS12 in photoreceptor maintenance, consistent with its inherited ciliary assembly role and retinal disease phenotype. Reason: Retain the phylogenetic assertion as a tissue-specific outcome of BBSome assembly. No target-specific loss or conflicting node placement was established; the family tree was not independently reconstructed. |
| GO:0051131 chaperone-mediated protein complex assembly | IBA GO_REF:0000033 | ACCEPT | Summary: BBS12 participates in the chaperonin-assisted assembly of the BBSome. Reason: The IBA is concordant with BBS12-containing assembly complexes and BBS12-depletion effects on BBSome assembly. This is a central biological process for BBS12. |
| GO:0005524 ATP binding | IEA GO_REF:0000002 | UNDECIDED | Summary: The InterPro ATP-binding inference is uncertain for this divergent chaperonin-like protein. Reason: The InterPro inference is weakened by published divergence of the BBS12 nucleotide-binding region, including the ATP-contacting GP motif. PMID:24010126 relates its non-vertebrate comparison explicitly to divergence previously reported in vertebrate orthologs. This is relevant to BBS12, but sequence divergence does not determine whether human BBS12 retains ATP binding. Binding and hydrolysis are distinct activities; the reviewed studies do not directly measure either for human BBS12. The activity remains unresolved. Supporting Evidence: PMID:24010126 In BBS12, the ADP/ATP-binding motif was less conserved, including substantial variability of the crucial GP dipeptide. |
| GO:0005929 cilium | IEA GO_REF:0000044 | MODIFY | Summary: Curated localization places BBS12 at the basal body of primary cilia in differentiating preadipocytes. Reason: Ciliary basal body is the specific compartment named in the UniProt source note and the 2009 primary abstract, and is part of the broader cilium. Refine the electronic localization accordingly. This does not imply exclusive basal-body localization or absence from the axoneme. The 2025 transfection abstract describes primary-cilium localization but does not distinguish basal body from shaft or establish a universal distribution. Proposed replacements: ciliary basal body |
| GO:0051131 chaperone-mediated protein complex assembly | IEA GO_REF:0000002 | ACCEPT | Summary: The BBS12-specific InterPro mapping to chaperone-mediated protein complex assembly is supported by experiments. Reason: BBS12 participates in an assembly intermediate with other chaperonin-like BBS proteins and CCT proteins, and its depletion disrupts BBSome assembly. Retain this core process alongside the independently grounded IBA and IMP rows. |
| GO:0005515 protein binding | IPI PMID:20080638 BBS6, BBS10, and BBS12 form a complex with CCT/TRiC family c... | KEEP AS NON CORE | Summary: The BBS9-scoped source records association with BBS12 in the BBSome assembly context. Reason: The unchanged GOA supporting entity is BBS9/Q3SYG4. The primary co-immunoprecipitation and purification experiments support the recorded interactions. They explain assembly participation but do not demonstrate that BBS12 itself folds a bound substrate. Preserve the generic interaction as non-core and remove the unsupported protein-folding-chaperone replacement. |
| GO:0005515 protein binding | IPI PMID:22500027 Intrinsic protein-protein interaction-mediated and chaperoni... | KEEP AS NON CORE | Summary: The BBS7-scoped source records association with BBS12 in the BBSome assembly context. Reason: The unchanged GOA supporting entity is BBS7/Q8IWZ6. The primary paper places BBS12 in the BBS-chaperonin complex and describes its release during formation of the BBSome core. These associations support the interaction annotation; they do not identify a direct BBS12 folding reaction or justify converting every associated partner to a folding substrate. |
| GO:0005515 protein binding | IPI PMID:26900326 A novel H395R mutation in MKKS/BBS6 causes retinitis pigment... | KEEP AS NON CORE | Summary: The MKKS/BBS6-scoped source records association with BBS12 in the BBSome assembly context. Reason: The unchanged GOA supporting entity is MKKS/BBS6/Q9NPJ1. The paper explicitly cotransfected Myc-tagged wild-type BBS12 and FLAG-tagged wild-type or mutant MKKS in HEK293T and ARPE-19 cells. The H395R MKKS variant reduced association to different extents in the two cell lines. This directly supports the interaction despite the paper foregrounding MKKS, but does not establish BBS12 protein-folding activity. Preserve the interaction as non-core. |
| GO:0005515 protein binding | IPI PMID:28514442 Architecture of the human interactome defines protein commun... | KEEP AS NON CORE | Summary: The BBS7-scoped source records association with BBS12 in the BBSome assembly context. Reason: The unchanged GOA supporting entity is BBS7/Q8IWZ6. Retain the curator-supported AP-MS interaction as non-core. The independent assembly literature supports its biological context, while AP-MS association does not establish direct binding, a folding substrate, or a particular catalytic mechanism. The old folding replacement is unsupported. |
| GO:0005515 protein binding | IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... | KEEP AS NON CORE | Summary: The BBS7-scoped source records association with BBS12 in the BBSome assembly context. Reason: The unchanged GOA supporting entity is BBS7/Q8IWZ6. The recorded partners fit the independently established assembly complex, so retain the interaction as non-core. Cell-specific AP-MS associations do not establish intrinsic BBS12 folding activity. No replacement molecular function is sufficiently established for each exact recorded interaction. |
| GO:0045599 negative regulation of fat cell differentiation | IMP PMID:22958920 BBS-induced ciliary defect enhances adipogenesis, causing pa... | KEEP AS NON CORE | Summary: BBS12 inactivation promotes adipogenic differentiation in human primary mesenchymal stem cells. Reason: The primary abstract explicitly reports increased adipogenesis following BBS12 inactivation, consistent with the negative-regulation direction. Retain the developmental/metabolic outcome as non-core relative to BBSome assembly. The abstract also reports Bbs12-knockout mouse metabolic phenotypes; those are not substituted for the human MSC experiment. |
| GO:0051131 chaperone-mediated protein complex assembly | IMP PMID:20080638 BBS6, BBS10, and BBS12 form a complex with CCT/TRiC family c... | ACCEPT | Summary: Experimental loss of BBS12 disrupts BBSome assembly. Reason: BBS12 depletion in cultured cells prevents normal association of BBSome components, while physical-complex experiments place BBS12 in the assembly machinery. Together these establish participation in chaperone-mediated complex assembly rather than merely a disease-level requirement. |
| GO:0005515 protein binding | IPI PMID:20080638 BBS6, BBS10, and BBS12 form a complex with CCT/TRiC family c... | KEEP AS NON CORE | Summary: The BBS7-scoped source records association with BBS12 in the BBSome assembly context. Reason: The unchanged GOA supporting entity is BBS7/Q8IWZ6. The primary co-immunoprecipitation and purification experiments support the recorded interactions. They explain assembly participation but do not demonstrate that BBS12 itself folds a bound substrate. Preserve the generic interaction as non-core and remove the unsupported protein-folding-chaperone replacement. |
| GO:0005515 protein binding | IPI PMID:20080638 BBS6, BBS10, and BBS12 form a complex with CCT/TRiC family c... | KEEP AS NON CORE | Summary: The BBS10-scoped source records association with BBS12 in the BBSome assembly context. Reason: The unchanged GOA supporting entity is BBS10/Q8TAM1. The primary co-immunoprecipitation and purification experiments support the recorded interactions. They explain assembly participation but do not demonstrate that BBS12 itself folds a bound substrate. Preserve the generic interaction as non-core and remove the unsupported protein-folding-chaperone replacement. |
| GO:0005515 protein binding | IPI PMID:20080638 BBS6, BBS10, and BBS12 form a complex with CCT/TRiC family c... | KEEP AS NON CORE | Summary: The BBS2-scoped source records association with BBS12 in the BBSome assembly context. Reason: The unchanged GOA supporting entity is BBS2/Q9BXC9. The primary co-immunoprecipitation and purification experiments support the recorded interactions. They explain assembly participation but do not demonstrate that BBS12 itself folds a bound substrate. Preserve the generic interaction as non-core and remove the unsupported protein-folding-chaperone replacement. |
| GO:0005515 protein binding | IPI PMID:20080638 BBS6, BBS10, and BBS12 form a complex with CCT/TRiC family c... | KEEP AS NON CORE | Summary: The MKKS/BBS6-scoped source records association with BBS12 in the BBSome assembly context. Reason: The unchanged GOA supporting entity is MKKS/BBS6/Q9NPJ1. The primary co-immunoprecipitation and purification experiments support the recorded interactions. They explain assembly participation but do not demonstrate that BBS12 itself folds a bound substrate. Preserve the generic interaction as non-core and remove the unsupported protein-folding-chaperone replacement. |
| GO:0005515 protein binding | IPI PMID:22500027 Intrinsic protein-protein interaction-mediated and chaperoni... | KEEP AS NON CORE | Summary: The MKKS/BBS6-scoped source records association with BBS12 in the BBSome assembly context. Reason: The unchanged GOA supporting entity is MKKS/BBS6/Q9NPJ1. The primary paper places BBS12 in the BBS-chaperonin complex and describes its release during formation of the BBSome core. These associations support the interaction annotation; they do not identify a direct BBS12 folding reaction or justify converting every associated partner to a folding substrate. |
| GO:0005515 protein binding | IPI PMID:28514442 Architecture of the human interactome defines protein commun... | KEEP AS NON CORE | Summary: The MKKS/BBS6-scoped source records association with BBS12 in the BBSome assembly context. Reason: The unchanged GOA supporting entity is MKKS/BBS6/Q9NPJ1. Retain the curator-supported AP-MS interaction as non-core. The independent assembly literature supports its biological context, while AP-MS association does not establish direct binding, a folding substrate, or a particular catalytic mechanism. The old folding replacement is unsupported. |
| GO:0005515 protein binding | IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... | KEEP AS NON CORE | Summary: The MKKS/BBS6-scoped source records association with BBS12 in the BBSome assembly context. Reason: The unchanged GOA supporting entity is MKKS/BBS6/Q9NPJ1. The recorded partners fit the independently established assembly complex, so retain the interaction as non-core. Cell-specific AP-MS associations do not establish intrinsic BBS12 folding activity. No replacement molecular function is sufficiently established for each exact recorded interaction. |
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Download this section (compressed HTML)Q: Which physical step does BBS12 perform during BBS7 engagement and release from the BBS-chaperonin machinery, and can it be separated from the contributions of MKKS/BBS6 and CCT proteins?
Q: Does human BBS12 bind a nucleotide under physiological conditions, despite divergence of the motifs identified in comparative sequence studies, and does nucleotide occupancy affect assembly?
Q: How does the ciliary defect caused by BBS12 depletion alter the adipogenic behavior of human mesenchymal stem cells?
Experiment: Reconstitute BBS12 with defined combinations of MKKS/BBS6, BBS7, BBS10 and CCT. Compare substrate conformation, complex formation and subunit release while directly measuring nucleotide binding and hydrolysis by the individual proteins and complete assemblies.
Hypothesis: BBS12 makes a specific assembly contribution that can be measured independently of the ATP-dependent folding activity of CCT.
Type: biochemical reconstitution
Experiment: Compare verified BBS12 variants at matched protein abundance and folding state before measuring association with MKKS/BBS6 and BBS7 and assessing BBSome assembly and ciliary phenotypes in cells.
Hypothesis: Some disease-associated interaction defects arise from reduced BBS12 stability rather than loss of a particular partner contact.
Type: controlled structure-function analysis
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