BBSome ciliary trafficking complex module

The BBSome is a conserved octameric protein complex that acts as a coat-like adaptor for ciliary membrane-protein trafficking. It is built from eight core subunits (BBS1, BBS2, BBS4, BBS5, BBS7, BBS8/TTC8, BBS9, and BBIP1/BBS18), assembled with the help of a dedicated chaperonin-like module (BBS6/MKKS, BBS10, BBS12 acting with the CCT/TRiC chaperonin). Once assembled, the BBSome is recruited to the ciliary membrane by the GTP-bound Arf-like GTPase ARL6/BBS3, where it polymerizes into a coat that recognizes signaling-receptor cargo (ciliary GPCRs and Hedgehog-pathway components) and couples them to the intraflagellar transport (IFT) machinery, mediating ciliary import and, especially, retrieval/export across the transition zone. LZTFL1/BBS17 and the accessory factor CCDC28B regulate BBSome ciliary trafficking. Loss of BBSome function causes Bardet-Biedl syndrome. This module models the BBSome as a cellular component / protein complex grounded in GO:0034464, capturing its composition, assembly, membrane recruitment, cargo trafficking, and regulation.

MODULE:bbsomeDRAFTProtein Complexmodules/bbsome.yaml
BBSomeGO:0034464 intraciliary transportGO:0042073
PMID:17574030
A core complex of BBS proteins cooperates with the GTPase Rab8 to promote ciliary membrane biogenesis
Identifies the BBSome as a stable complex of seven BBS proteins plus BBIP10 that associates with the ciliary membrane and promotes ciliary membrane trafficking.
PMID:19081074
A BBSome subunit links ciliogenesis, microtubule stability, and acetylation
Establishes BBIP10 (BBIP1) as an integral eighth BBSome subunit required for complex integrity and links the BBSome to microtubule stability and acetylation.
PMID:20603001
The conserved Bardet-Biedl syndrome proteins assemble a coat that traffics membrane proteins to cilia
Shows the BBSome forms a planar coat on membranes whose assembly is nucleated by ARL6/BBS3-GTP, supporting the coat-adaptor model for ciliary cargo trafficking.
PMID:25402481
Structural basis for membrane targeting of the BBSome by ARL6
Provides the structural basis for GTP-dependent recruitment of the BBSome to membranes by ARL6/BBS3 via the BBS1 beta-propeller.
PMID:20080638
BBS6, BBS10, and BBS12 form a complex with CCT/TRiC family chaperonins and mediate BBSome assembly
Demonstrates that the chaperonin-like BBS proteins (MKKS/BBS6, BBS10, BBS12) act with the CCT/TRiC chaperonin to assemble the BBSome core, supporting a dedicated assembly module distinct from the mature complex.
PMID:22072986
A novel protein LZTFL1 regulates ciliary trafficking of the BBSome and Smoothened
Shows LZTFL1/BBS17 regulates ciliary entry and retrieval of the BBSome and of Smoothened, supporting a trafficking-regulation interface to the complex.

This module is intentionally BBSome-centric: it represents the eight-subunit core complex, its dedicated chaperonin-like assembly module, its ARL6/BBS3 membrane recruiter, and its LZTFL1/CCDC28B trafficking regulators. Broader ciliary machinery that the BBSome cooperates with (the IFT-A/IFT-B trains, the transition-zone MKS/NPHP modules, and Rab8/Rab23 membrane-trafficking regulators) is treated as an interface rather than part of the complex. Several proteins carry "BBS" disease-locus numbers but belong primarily to other ciliary modules (e.g. IFT27/BBS19, IFT172/BBS20, MKS1/BBS13, CEP290/BBS14, SDCCAG8/BBS16, WDPCP/BBS15) and are out of scope here. Subunit roles reflect the cryo-EM/biochemical consensus; where a precise GO molecular function is uncertain, only a preferred_term and description are given.

6Nodes
5Parts
0Variant Sets
0Variants
6Annotons
4Connections

Derived QC

Recommended-field compliance

100.0% recommended fields populated

All recommended fields populated.

Module deep research

✗ none found

No MODULE:bbsome deep-research report alongside the module YAML.

Leaf nodes lacking representative members

1 leaf node(s) with no concrete protein grounding:

Template conformance

✓ every declared conforms_to bundle matches its template motif.

Gene-review completeness (14/14 grounded genes reviewed)

14 complete review(s) · 8 with deep research · 0 missing review · 6 reviewed but lacking deep research

Gene Review Complete Deep research
ARL6 Q9H0F7 ✓ ✓ ✓
BBIP1 A8MTZ0 ✓ ✓ ✓
BBS1 Q8NFJ9 ✓ ✓ ✗
BBS10 Q8TAM1 ✓ ✓ ✓
BBS12 Q6ZW61 ✓ ✓ ✓
BBS2 Q9BXC9 ✓ ✓ ✗
BBS4 Q96RK4 ✓ ✓ ✗
BBS5 Q8N3I7 ✓ ✓ ✗
BBS7 Q8IWZ6 ✓ ✓ ✗
BBS9 Q3SYG4 ✓ ✓ ✗
CCDC28B Q9BUN5 ✓ ✓ ✓
LZTFL1 Q9NQ48 ✓ ✓ ✓
MKKS Q9NPJ1 ✓ ✓ ✓
TTC8 Q8TAM2 ✓ ✓ ✓

Details

Context
ciliated eukaryotes
ciliumGO:0005929 ciliary membraneGO:0060170 ciliary basal bodyGO:0036064 ciliary tipGO:0097542
BBSome ciliary trafficking complexProtein Complexbbsome
BBSomeGO:0034464 intraciliary transportGO:0042073
Context
ciliated eukaryotes
ciliumGO:0005929 ciliary membraneGO:0060170 ciliary basal bodyGO:0036064 ciliary tipGO:0097542

Connections

Chaperonin-mediated assembly produces the mature BBSome octamer.
The assembled octamer is the substrate recruited to the ciliary membrane by ARL6/BBS3.
Membrane recruitment positions the BBSome coat to capture cargo and couple it to IFT.
LZTFL1/CCDC28B regulate BBSome ciliary entry and cargo retrieval.
Part 1: assembly of the BBSome core by chaperonin-like factors
Chaperonin-mediated BBSome assemblyProtein Complexbbsome_assembly

The chaperonin-like BBS proteins MKKS/BBS6, BBS10, and BBS12 form a complex with the CCT/TRiC chaperonin that folds BBS7 and nucleates assembly of the eight-subunit BBSome core. These factors are required to build the complex but are not stable subunits of the mature BBSome.

chaperone-mediated protein complex assemblyGO:0051131

Annotons

BBS chaperonin-like assembly module (BBS6/BBS10/BBS12 + CCT)
bbs_chaperonin_assembly_module
Participant: Protein Complex: BBS chaperonin-like assembly complex with CCT/TRiC
Protein Complex:
BBS chaperonin-like assembly complex with CCT/TRiC Chaperonin-like BBS proteins acting with the cytosolic CCT/TRiC chaperonin to assemble the BBSome core.
Active units:
MKKS/BBS6 chaperonin-like unit
Participant: Gene Product: MKKS (BBS6)
Gene Product:
MKKS (BBS6)UniProtKB:Q9NPJ1
Role: chaperonin-like assembly factor
Function:
protein folding chaperoneGO:0044183
BBS10 chaperonin-like unit
Participant: Gene Product: BBS10
Gene Product:
BBS10UniProtKB:Q8TAM1
Role: chaperonin-like assembly factor
BBS12 chaperonin-like unit
Participant: Gene Product: BBS12
Gene Product:
BBS12UniProtKB:Q6ZW61
Role: chaperonin-like assembly factor
CCT/TRiC chaperonin
Participant: Protein Complex: CCT/TRiC chaperonin
Protein Complex:
CCT/TRiC chaperonin Cytosolic chaperonin containing TCP-1 (TRiC) that cooperates with the BBS chaperonins.
Role: cytosolic chaperonin that folds BBSome subunits

Function

chaperone-mediated assembly of the BBSome coreGO:0051131
Targets: BBSome core subunits
PMID:20080638
BBS6/BBS10/BBS12 form a complex with CCT/TRiC chaperonins and mediate BBSome assembly.
Part 2: mature BBSome core complex
BBSome core octamerProtein Complexbbsome_core_octamer

The mature eight-subunit BBSome. BBS2, BBS7, and BBS9 form an interlocking beta-propeller/GAE/platform scaffold; BBS1 is the principal cargo- and ARL6/BBS3-interaction subunit; BBS4 and BBS8/TTC8 are TPR-superhelix adaptors; BBS5 contributes phosphoinositide-binding pleckstrin-homology domains for membrane association; and the small BBIP1/BBS18 subunit is required for complex integrity.

BBSomeGO:0034464

Annotons

BBSome octamer subunits
bbsome_octamer_units
Participant: Protein Complex: BBSome octamer
Protein Complex:
BBSome octamerGO:0034464
Active units:
BBS1 subunit1
Participant: Gene Product: BBS1
Gene Product:
BBS1UniProtKB:Q8NFJ9
Role: beta-propeller subunit; principal cargo recognition and ARL6/BBS3-GTP binding interface
BBS2 subunit1
Participant: Gene Product: BBS2
Gene Product:
BBS2UniProtKB:Q9BXC9
Role: beta-propeller/GAE/platform scaffold subunit
BBS4 subunit1
Participant: Gene Product: BBS4
Gene Product:
BBS4UniProtKB:Q96RK4
Role: TPR-superhelix adaptor subunit
BBS5 subunit1
Participant: Gene Product: BBS5
Gene Product:
BBS5UniProtKB:Q8N3I7
Role: pleckstrin-homology subunit; phosphoinositide-dependent membrane association
Function:
phosphatidylinositol-3-phosphate bindingGO:0032266
BBS7 subunit1
Participant: Gene Product: BBS7
Gene Product:
BBS7UniProtKB:Q8IWZ6
Role: beta-propeller/GAE/platform scaffold subunit; CCT/chaperonin client during assembly
BBS8/TTC8 subunit1
Participant: Gene Product: TTC8 (BBS8)
Gene Product:
TTC8 (BBS8)UniProtKB:Q8TAM2
Role: TPR-superhelix adaptor subunit
BBS9 subunit1
Participant: Gene Product: BBS9
Gene Product:
BBS9UniProtKB:Q3SYG4
Role: central beta-propeller/GAE/platform/alpha-helical scaffold subunit
BBIP1/BBS18 subunit1
Participant: Gene Product: BBIP1 (BBIP10, BBS18)
Gene Product:
BBIP1 (BBIP10, BBS18)UniProtKB:A8MTZ0
Role: small subunit required for BBSome integrity; links to microtubule stability/acetylation

Function

ciliary membrane-protein cargo adaptor The assembled octamer functions as a coat-like adaptor that selects membrane-protein cargo for intraflagellar transport.

Locations

ciliary membraneGO:0060170 ciliary basal bodyGO:0036064
PMID:17574030
Defines the seven-subunit BBSome plus BBIP10 associated with the ciliary membrane.
PMID:19081074
Establishes BBIP10/BBIP1 as the integral eighth subunit required for complex integrity.
Part 3: GTP-dependent membrane recruitment
ARL6/BBS3 membrane recruitment of the BBSomeRegulatory Steparl6_membrane_recruitment

The Arf-like GTPase ARL6/BBS3, in its GTP-bound state, binds the BBS1 beta-propeller and recruits the BBSome to the ciliary membrane, where BBSome coat polymerization is nucleated. This is the membrane-targeting switch for BBSome function.

Annotons

ARL6/BBS3 GTP-dependent BBSome recruitment
arl6_gtpase_recruitment
Participant: Gene Product: ARL6 (BBS3)
Gene Product:
ARL6 (BBS3)UniProtKB:Q9H0F7

Function

GTP-dependent recruitment of the BBSome to the ciliary membraneGO:0005525
Targets: BBSomeGO:0034464

Locations

ciliary membraneGO:0060170
PMID:20603001
ARL6/BBS3-GTP nucleates BBSome coat assembly on membranes.
PMID:25402481
Structural basis for ARL6-GTP recruitment of the BBSome via the BBS1 beta-propeller.
Part 4: cargo recognition and ciliary trafficking
BBSome cargo recognition and ciliary import/retrievalTransport Stepbbsome_cargo_trafficking

The membrane-bound BBSome recognizes signaling-receptor cargo (ciliary GPCRs such as SSTR3, MCHR1, NPY2R, and Hedgehog-pathway components such as Smoothened and GPR161) and couples them to the IFT trains. The BBSome is especially required for retrieval/export of activated receptors out of the cilium across the transition zone.

protein localization to ciliumGO:0061512

Annotons

BBSome ciliary cargo adaptor activity
bbsome_cargo_adaptor
Participant: Protein Complex: membrane-bound BBSome coat
Protein Complex:
membrane-bound BBSome coatGO:0034464

Function

ciliary membrane-protein cargo adaptor coupling to intraflagellar transportGO:0042073
Cargo: ciliary GPCR cargo (e.g. SSTR3, MCHR1, NPY2R) Hedgehog signaling components (Smoothened, GPR161)

Locations

ciliary membraneGO:0060170 ciliary tipGO:0097542 ciliary transition zoneGO:0035869
PMID:20603001
The BBSome coat traffics membrane proteins to and within cilia.
Part 5: regulation of BBSome ciliary trafficking (optional)
Regulation of BBSome ciliary traffickingRegulatory Stepbbsome_trafficking_regulation

LZTFL1/BBS17 and the accessory factor CCDC28B regulate BBSome ciliary entry and retrieval. LZTFL1 associates with the BBSome in the cytoplasm and controls ciliary trafficking of the BBSome and Smoothened.

Annotons

LZTFL1/BBS17 regulation of BBSome ciliary trafficking
lztfl1_regulation
Participant: Gene Product: LZTFL1 (BBS17)
Gene Product:
LZTFL1 (BBS17)UniProtKB:Q9NQ48

Function

regulation of BBSome and Smoothened ciliary localizationGO:1903565
Targets: BBSomeGO:0034464 Smoothened
PMID:22072986
LZTFL1 regulates ciliary trafficking of the BBSome and Smoothened.
CCDC28B accessory modifier of BBSome ciliary localization
ccdc28b_modifier
Participant: Gene Product: CCDC28B
Gene Product:
CCDC28BUniProtKB:Q9BUN5

Function

modifier of BBSome ciliary localization Accessory factor that influences BBSome ciliary localization; acts as a genetic modifier of Bardet-Biedl syndrome rather than a core subunit. No precise GO molecular function is asserted here.

Accessory modifier of BBSome ciliary trafficking.