| Category | ARL6-specific finding | Key details | Evidence |
|---|---|---|---|
| Protein identity | **ARL6** encodes **ADP-ribosylation factor-like protein 6** and is also called **BBS3** | ARL6/BBS3 is a member of the ARF/ARL small GTPase family and is part of the conserved core BBS machinery linked to cilia and Bardet-Biedl syndrome | (pqac-00000002, pqac-00000009, pqac-00000007) |
| Molecular function as a GTPase | Small **ARF-like GTP-binding protein** with **intrinsic GTPase activity** | Functions as a nucleotide-dependent molecular switch; the **GTP-bound** form is the functionally relevant state for BBSome recruitment, and ARL6 has been described as having intrinsic GTPase activity in recent mechanistic work | (pqac-00000003, pqac-00000005, pqac-00000007) |
| Primary biochemical role | **Recruits the BBSome to membranes/cilia** | ARL6:GTP binds the BBSome and promotes its targeting to the **basal body/ciliary membrane**, a prerequisite for BBSome-dependent trafficking across the transition zone | (pqac-00000002, pqac-00000005, pqac-00000015) |
| Structural mechanism | ARL6 recognizes a **composite BBSome binding site** | Cryo-EM work showed that ARL6 binds an **active** BBSome conformation, contacting a site formed by **BBS1 and BBS7**; BBS1 β-propeller movement is required to expose this site | (pqac-00000002, pqac-00000003, pqac-00000013) |
| Substrate/nucleotide specificity | Prefers/acts through **GTP-bound state** rather than GDP-bound state | The BBSome interacts with **only the GTP-bound form** of ARL6 in the structural purification/reconstitution studies, indicating nucleotide-state specificity for effector engagement | (pqac-00000003) |
| Enzymatic interpretation | Not a metabolic enzyme; its key “substrate” is **guanine nucleotide cycling** | For this protein, the relevant biochemical activity is **binding and hydrolysis of GTP** to regulate effector recruitment rather than catalysis of a small-molecule transformation | (pqac-00000007, pqac-00000005) |
| Subcellular localization | **Primary cilium**, **ciliary membrane**, and **basal body/ciliary base** | Reviews and primary studies place ARL6 at the ciliary compartment, where it helps recruit the BBSome; BBS-related proteins are concentrated at the ciliary base and within ciliary trafficking routes | (pqac-00000002, pqac-00000005, pqac-00000001, pqac-00000010) |
| Membrane association | Associates with membranes in a **GTP-dependent** manner | As an Arf-family GTPase with an amphipathic N-terminus, ARL6 is described as associating with membranes when GTP-bound, consistent with its role in docking trafficking machinery to ciliary membranes | (pqac-00000002) |
| Principal binding partners/effectors | **BBSome**, especially **BBS1** and **BBS7**; BBS1 interaction reinforced by **BBS9** | ARL6 directly binds the BBSome through BBS1-containing interfaces; cell and biochemical work indicates that BBS9 strengthens the ARL6–BBS1 interaction within the intact BBSome core | (pqac-00000002, pqac-00000008, pqac-00000005) |
| Functional relationship to IFT | Works with **IFT/BBSome trafficking machinery** | ARL6 enables BBSome loading/recruitment so the BBSome can function as an adaptor linking membrane cargoes to intraflagellar transport for ciliary trafficking and exit | (pqac-00000005, pqac-00000009, pqac-00000015) |
| Role in pathway | Central regulator of **ciliary membrane protein trafficking** | ARL6 is required for proper movement of signaling receptors and other membrane proteins through the ciliary compartment, especially at the **transition zone** and during **cargo export/removal** | (pqac-00000015, pqac-00000009, pqac-00000002) |
| Cargo/processes influenced | Supports trafficking of **GPCRs** and other ciliary membrane proteins | BBSome/ARL6 function is linked to the trafficking or removal of receptors such as **Smoothened, GPR161, SSTR3**, and other ciliary membrane proteins; defects cause receptor mislocalization | (pqac-00000008, pqac-00000006, pqac-00000002) |
| Signaling pathways impacted | Modulates **Hedgehog** and broader **cilium-dependent signaling** | Because ARL6 drives BBSome-dependent receptor trafficking, it indirectly controls signaling outputs that depend on receptor localization in cilia, including **Shh/Hedgehog** and GPCR signaling | (pqac-00000001, pqac-00000005, pqac-00000009) |
| Regulation noted in recent work | BBSome–ARL6 interaction can be enhanced by **BBS1 ubiquitylation** | A 2023 study reported that ubiquitylation of **BBS1 K143** increases BBSome stability and promotes binding to **BBS3/ARL6**, linking post-translational regulation to ARL6-dependent trafficking | (pqac-00000005) |
| Current unknowns | Upstream **GEF/GAP regulators for ARL6** remain incompletely defined | Reviews emphasize that, unlike some other ciliary ARLs, the dedicated regulators that activate/inactivate ARL6 are still not well established and remain a key knowledge gap | (pqac-00000007) |
| Disease association | **Bardet-Biedl syndrome type 3 (BBS3)** | ARL6 mutations cause a ciliopathy with multisystem manifestations; ARL6/BBS3 is one of the established BBS genes and belongs to the non-motile ciliopathy spectrum | (pqac-00000010, pqac-00000011, pqac-00000009) |
| Disease features linked to ARL6 dysfunction | Retinal degeneration, obesity, polydactyly, renal/genitourinary anomalies, learning/neurodevelopmental issues | These are core BBS features described across recent reviews and consensus guidance; ARL6 defects impair ciliary trafficking, providing the mechanistic basis for the phenotype spectrum | (pqac-00000010, pqac-00000011, pqac-00000001) |
| Clinical nuance | ARL6 deficiency may show **lower penetrance of some features**, including kidney anomalies, than some other BBS genotypes | Recent reviews/consensus statements note genotype-phenotype variability and specifically mention comparatively lower penetrance of renal manifestations in **BBS3/ARL6** deficiency | (pqac-00000011, pqac-00000010) |


*Table: This table summarizes the verified identity, molecular function, localization, interacting partners, pathway role, and disease relevance of human ARL6/BBS3. It is useful as a compact evidence map for understanding ARL6 as a ciliary ARF-like GTPase that recruits the BBSome and whose disruption causes Bardet-Biedl syndrome.*