FBXO17

Gap: The physiological glycoprotein substrates and glycan determinants recognized by FBXO17 remain unresolved.

OPEN BIOLOGYCURATION MF_DARK

What is known: The review already accepts FBXO17 carbohydrate binding and glycoprotein catabolism, and it rejects broad ERAD/high-mannose propagation. The remaining gap is which endogenous complex-type or sulfated glycoproteins are FBXO17 substrates and in what cytosolic or secretory-interface context FBXO17 encounters them.

Significance: Resolving this gap would define the substrate-recognition specificity that distinguishes FBXO17 from high-mannose-binding FBA proteins and would prevent over-propagating ERAD/glycoprotein quality-control annotations from related family members.

What would resolve it: Endogenous substrate discovery should pair FBXO17 perturbation with glycoproteomics and glycan-dependence assays, testing candidate complex-type and sulfated glycoproteins against FBA/G-domain binding-pocket mutants.

Provenance (the field's own admissions):

• "FBXO17 bound heparin strongly and chondroitin sulfate weakly, suggesting that FBXO17 binds sulfated glycans." — PMID:18203720
• "Because FBXO17 did not bind high mannose glycans on the glycan array, its binding to lactoferrin likely reflects binding to the complex glycan moieties on the protein." — PMID:18203720
• "The “cytosolic N-glycans” review highlights that F-box proteins act as SCF substrate-recognition subunits and places FBXO17 in a phylogenetic context with related glycan-recognizing FBXOs, consistent with the idea that FBXO17 may possess carbohydrate-recognition-like features (though substrate glycan recognition is not directly validated in the retrieved core mechanistic papers)." — file:human/FBXO17/FBXO17-deep-research-falcon.md

Gap: Whether recognition of the validated GSK3-beta substrate is glycan-dependent and how broad FBXO17's protein-substrate repertoire is remains unresolved.

NARROWING BIOLOGYCURATION MF_DARK

What is known: The review already treats GSK3-beta as a validated FBXO17 substrate and separates this protein-substrate evidence from the lectin/glycoprotein core. The unresolved issue is whether GSK3-beta recognition uses the same FBA/G glycan-recognition machinery, a separate protein-binding surface, or context-specific bridging factors.

Significance: Resolving this gap would clarify whether FBXO17 should be represented as a lectin-specific substrate receptor, a broader protein-substrate receptor, or a dual-specificity adaptor with distinct substrate-recognition modes.

What would resolve it: Direct binding and ubiquitination assays comparing GSK3-beta, candidate glycoprotein substrates, FBA/G pocket mutants, and the mapped 151-200 GSK3-beta-binding region should establish whether the substrate classes are mechanistically separable.

Provenance (the field's own admissions):

• "A detailed biochemical study in lung epithelial cells shows that **FBXO17 associates with GSK3β**, promotes **polyubiquitination** of GSK3β, and drives **proteasome-dependent turnover** of GSK3β." — file:human/FBXO17/FBXO17-deep-research-falcon.md
• "Mapping a **putative GSK3β-binding region** in FBXO17 (amino acids **151–200** required for association in the reported assays)." — file:human/FBXO17/FBXO17-deep-research-falcon.md
• "Beyond GSK3β and IRF3/PP2A scaffolding, additional direct substrates of FBXO17 in human tissues are not established in the retrieved corpus and represent a key opportunity for future work." — file:human/FBXO17/FBXO17-deep-research-falcon.md

Gap: How FBXO17 partitions canonical SCF substrate-receptor activity from F-box-independent IRF3/PP2A signaling and tissue-specific pathway effects remains unresolved.

OPEN BIOLOGYCURATION BP_DARK

What is known: The review already captures canonical SCF substrate-adaptor function and records the IRF3/PP2A mechanism as a strong non-canonical lead. The remaining gap is how domains, post-translational signals, tissue context, or binding partners switch FBXO17 between ubiquitin-ligase adaptor and phosphatase-recruiting scaffold modes.

Significance: Resolving this gap would determine which immune and cancer pathway annotations are direct FBXO17 functions and which are downstream or model-specific consequences of perturbing GSK3-beta, IRF3, or other substrates.

What would resolve it: Separation-of-function alleles that disrupt the F-box, FBA/G domain, IRF3/PP2A recruitment region, and GSK3-beta-binding region should be tested side by side in immune and cancer contexts with direct ubiquitination, dephosphorylation, and pathway readouts.

Provenance (the field's own admissions):

• "FBXO17 can regulate signaling **independently of its canonical SCF function** by recruiting **PP2A** to the transcription factor **IRF3** to promote IRF3 dephosphorylation and suppress type I interferon signaling. This is explicitly described as not requiring the F-box domain and using the “F-box associated region.”" — file:human/FBXO17/FBXO17-deep-research-falcon.md
• "Interpretation: these studies indicate FBXO17 influences major signaling hubs (GSK3β, Akt/ERK, Wnt/β-catenin), but the **directionality** of pathway changes is model-dependent and not yet reconciled into a single unified mechanism across tissues." — file:human/FBXO17/FBXO17-deep-research-falcon.md
• "Tissue-specific directionality (oncogenic vs tumor-suppressive) and reconciliation of pathway effects across cancer models remain unresolved." — file:human/FBXO17/FBXO17-deep-research-falcon.md