Human BBSome Project

Overview

The BBSome is an octameric protein complex (GO:0034464) that functions as a
coat-like adaptor for ciliary membrane-protein trafficking. It recognizes signaling
receptor cargo (e.g. GPCRs such as SSTR3, MCHR1, the Hedgehog effectors SMO and GPR161)
and couples them to the intraflagellar transport (IFT) machinery, mediating both
import into and, especially, retrieval/export out of the primary cilium across the
transition zone. BBSome dysfunction causes Bardet–Biedl syndrome (BBS), a
pleiotropic ciliopathy featuring retinal degeneration, obesity, polydactyly, renal
anomalies, hypogonadism, and cognitive impairment.

This project reviews the GO annotations of the BBS-associated genes and builds a
reusable cell-component module for the BBSome under modules/bbsome.yaml.

Complex architecture

Core BBSome (octamer): BBS1, BBS2, BBS4, BBS5, BBS7, TTC8 (BBS8), BBS9, BBIP1 (BBS18).
BBS2/BBS7/BBS9 form a β-propeller/GAE/platform core; BBS1 is the principal cargo/ARL6
interaction subunit; BBS4 and BBS8 (TPR subunits) and BBS5 (PH-domain, PtdIns binding)
and the small BBIP1 stabilize the assembly.
Membrane recruiter: ARL6 (BBS3), an Arf-like small GTPase that, in its GTP-bound
state, recruits the BBSome to the ciliary membrane and polymerizes the coat.
Trafficking regulator: LZTFL1 (BBS17) regulates BBSome ciliary entry/retrieval and
associates with the complex in the cytoplasm.
BBS chaperonin complex (assembly factors, not BBSome subunits): MKKS (BBS6),
BBS10, BBS12 — three chaperonin-like proteins that, with CCT/TRiC, assemble the BBSome
core. CCDC28B is an accessory modifier of BBSome ciliary localization.

Note: Other "BBS" loci (e.g. IFT27/BBS19, IFT172/BBS20, MKS1/BBS13, CEP290/BBS14,
SDCCAG8/BBS16, WDPCP/BBS15, C8orf37/BBS21, TRIM32/BBS11) belong primarily to the IFT,
transition-zone, or other ciliary modules and are out of scope for this BBSome-centric
project (candidates for separate IFT / transition-zone modules).

Genes for Review

#	HGNC	BBS locus	UniProt	Role
1	BBS1	BBS1	Q8NFJ9	Core subunit; principal cargo/ARL6 interface
2	BBS2	BBS2	Q9BXC9	Core subunit; β-propeller core
3	ARL6	BBS3	Q9H0F7	Arf-like GTPase; membrane recruitment of BBSome
4	BBS4	BBS4	Q96RK4	Core subunit; TPR adaptor
5	BBS5	BBS5	Q8N3I7	Core subunit; PH domains, phosphoinositide binding
6	MKKS	BBS6	Q9NPJ1	Chaperonin-like; BBSome assembly
7	BBS7	BBS7	Q8IWZ6	Core subunit; β-propeller core
8	TTC8	BBS8	Q8TAM2	Core subunit; TPR adaptor
9	BBS9	BBS9	Q3SYG4	Core subunit; platform/scaffold
10	BBS10	BBS10	Q8TAM1	Chaperonin-like; BBSome assembly
11	BBS12	BBS12	Q6ZW61	Chaperonin-like; BBSome assembly
12	LZTFL1	BBS17	Q9NQ48	Regulates BBSome ciliary trafficking
13	BBIP1	BBS18	A8MTZ0	Core subunit; complex stabilization
14	CCDC28B	—	Q9BUN5	Accessory modifier of BBSome ciliary localization

(UniProt IDs to be confirmed from fetched records.)

Deliverables

modules/bbsome.yaml — cell-component module (ModuleReview, CELLULAR_COMPONENT/
PROTEIN_COMPLEX) describing BBSome composition, assembly, recruitment, and cargo
trafficking, grounded in GO:0034464.
Per-gene genes/human/<GENE>/<GENE>-ai-review.yaml — full annotation reviews.
Per-gene <GENE>-notes.md research notes with cited provenance.

Project Status

[x] Define gene set (14 BBS-associated genes) and confirm scope (all BBS-associated)
[x] Fetch UniProt/GOA/publications for all genes
[x] Build modules/bbsome.yaml cell-component module (passes linkml-validate + term-validator)
[x] Per-gene annotation reviews (14/14)
[x] Validate all (module + all 14 gene reviews ✓ Valid)
[ ] Pathway/summary integration (optional follow-up)

Review summary (completed 2026-06-14)

All 14 gene reviews are complete and validate cleanly. Each gene received a
standalone description, full per-annotation review (action + summary + reason),
core_functions, suggested_questions/suggested_experiments, reference_review
blocks, and a <GENE>-notes.md research journal with cited provenance.

Gene	Ann (+NEW)	ACCEPT	Non-core	Over-ann.	MODIFY	REMOVE
BBS1	60	30	18	7	5	0
BBS2	67	16	24	25	0	2
ARL6	39	11	19	7	0	0
BBS4	110	42	37	31	0	0
BBS5	44	18	12	14	0	0
MKKS	61 (+1)	5	23	30	2	0
BBS7	48 (+1)	15	18	14	1	0
TTC8	47	23	10	14	0	0
BBS9	48 (+1)	20	13	13	2	0
BBS10	12 (+2)	5	4	3	0	0
BBS12	12 (+1)	3	3	6	0	0
LZTFL1	24	12	2	9	0	0
BBIP1	24 (+3)	13	8	3	0	0
CCDC28B	6	4	0	2	0	0

Cross-cutting findings:
- The pervasive uninformative protein binding (GO:0005515) IPI annotations were
consistently flagged (MARK_AS_OVER_ANNOTATED), with the real biology captured by
BBSome membership (GO:0034464) or specific MF terms (e.g. BBS1→small GTPase binding
for the ARL6/BBS3-GTP interaction).
- The chaperonin-like assembly factors (MKKS/BBS6, BBS10, BBS12) are correctly treated as
assembly factors, not structural BBSome subunits; their core MF is now the
non-obsolete GO:0044183 (protein folding chaperone) — the obsolete GO:0051082
(unfolded protein binding) surfaced during review was replaced here and in the module.
- A recurring RNA Pol II transcription factor binding (GO:0061629) annotation derived
from a BBS7-centric study (PMID:22302990) was flagged as MISCITED/DISPUTED across the
scaffold subunits.
- BBS2 had two over-propagated electronic (IEA) annotations (microvillus, stereocilium)
removed as biologically unsupported.

Key References

Nachury MV et al. (2007) Cell — Identification of the BBSome as a ciliary coat complex.
Loktev AV et al. (2008) Dev Cell — BBIP10/BBIP1 as the 8th BBSome subunit.
Jin H et al. (2010) Cell — ARL6/BBS3 recruits the BBSome; coat polymerization.
Klink BU et al. (2020) eLife / Singh SK et al. (2020) — Cryo-EM architecture of the BBSome.
Seo S et al. (2010) PNAS — BBS chaperonins (MKKS/BBS6, BBS10, BBS12) + CCT mediate BBSome assembly.
Nachury MV (2018) Phil Trans R Soc B — BBSome trafficking and ciliary GPCR retrieval.