## 2026-06-03 - Proteostasis PN review

- ARF1 is a class I ADP-ribosylation factor small GTPase whose core cellular role is regulated membrane recruitment of trafficking machinery at the Golgi/TGN. The core experimental model is a GTP/GDP cycle in which ARF-GTP triggers coat assembly and ARF GTP hydrolysis triggers coat disassembly [PMID:8253837 Hydrolysis of bound GTP by ARF protein triggers uncoating of Golgi-derived COP-coated vesicles, "Coat assembly is triggered when ARF binds GTP"].
- ARF1 is mechanistically tied to COPI dynamics but is not itself a coatomer subunit. The ARF1-ARFGAP-coatomer work supports ARF1 as the regulatory GTPase that controls COPI coat disassembly, not as a structural component of the COPI vesicle coat [PMID:10102276 Structural and functional analysis of the ARF1-ARFGAP complex reveals a role for coatomer in GTP hydrolysis, "a tripartite complex controls the GTP hydrolysis reaction triggering disassembly"].
- The PN projection places ARF1 under `ER proteostasis > Protein transport > ER-Golgi trafficking > Retrograde transport > COPI coating and uncoating`. The projected `GO:0006890 retrograde vesicle-mediated transport, Golgi to endoplasmic reticulum` is biologically reasonable for ARF1 because Reactome lists ARF1 in COPI-dependent Golgi-to-ER retrograde traffic and the cached pathway summary states that retrograde traffic from cis-Golgi to ERGIC/ER is mediated by COPI-coated vesicles [Reactome:R-HSA-6811434 COPI-dependent Golgi-to-ER retrograde traffic, "Retrograde traffic from the cis-Golgi to the ERGIC or the ER"].
- The projected `GO:0030126 COPI vesicle coat` should not be added for ARF1. This component term is suitable for coatomer subunits such as COPG1, but ARF1 is a membrane-associated regulatory GTPase that recruits and releases coat machinery. Adding the component term would imply ARF1 is part of the COPI vesicle coat rather than a regulator of COPI coating/uncoating.
- The broader PN-projected `GO:0015031 protein transport` is already entailed by ARF1 GOA through `GO:0006886 intracellular protein transport`, so it does not need a new annotation.
- ARF1 has additional validated but non-core contexts: FAPP2-dependent glycosphingolipid synthesis/export [PMID:17687330 Glycosphingolipid synthesis requires FAPP2 transfer of glucosylceramide, "sensitive to regulation by phosphatidylinositol 4-phosphate and ARF1"], PI4KB/NCS-1 interactions at the Golgi [PMID:17555535 Specificity, promiscuity and localization of ARF protein interactions with NCS-1 and phosphatidylinositol-4 kinase-III beta, "ARF1 but not ARF5 or 6 enhanced"], copper uptake through trafficking of CTR1 [PMID:21034850 The ADP-ribosylation factor 1 (Arf1) is involved in regulating copper uptake, "required for optimal copper uptake efficiency"], and recruitment to damaged lysosomal membranes without clear ARF1-specific repair requirement [PMID:41293316 Loss of ARF5 impairs recovery after lysosomal damage, "ARF1, ARF5, and ARF6 localize to lysosomal membranes"].
- Cytosol and endomembrane annotations are accurate localization context for a cycling peripheral membrane GTPase, but the active functional emphasis remains Golgi/TGN membrane recruitment and coat/adaptor regulation.
- The magnesium ion binding annotation is retained as a cofactor-level biochemical property of the nucleotide/GTPase mechanism, not as an independent biological role.
- Generic protein binding annotations are treated as over-annotated because ARF1 has many real effectors and regulators, but the term does not capture the informative activity: regulated small-GTPase recruitment of trafficking machinery.
- Generic protein-containing complex annotations are treated as over-annotated because ARF1 forms transient regulatory complexes with coat, adaptor, GEF, and GAP machinery rather than acting as a stable structural complex subunit.
- High-throughput-only focal adhesion, extracellular exosome, and RNA-binding annotations are treated as over-annotated because they do not define the established ARF1 Golgi/TGN trafficking function.
- Sarcomere localization and mitotic cleavage furrow ingression are not supported as core ARF1 biology in this review; the curated evidence supports Golgi/TGN endomembrane trafficking instead.
- Neuronal annotations transferred from orthology, including postsynaptic density, synapse, receptor internalization, Arp2/3 regulation, long-term synaptic depression, and dendritic spine organization, are retained only as non-core specialized contexts.
- Falcon deep research was launched with `just deep-research-falcon human ARF1 --fallback perplexity-lite`. The Falcon provider timed out after 600 seconds, and the `perplexity-lite` fallback failed with a 401 quota error, so no provider deep-research file was available for this pass. This review is therefore supported by the local GOA seed, UniProt, cached publications, cached Reactome records, and PN projection/mapping files.

## Falcon deep research findings (2026-06-07)

A Falcon (Edison Scientific) deep-research report (`ARF1-deep-research-falcon.md`, 32 citations) was generated on 2026-06-07 and reviewed against the existing COMPLETE review. Most content CONFIRMS existing annotations (GTPase cycle, COPI/cis-Golgi via GBF1, AP-1/TGN, PI4KB-PI4P, myristoyl switch, retrograde Golgi-to-ER, glycosphingolipid export). The following are the genuinely new or mechanistically refined items. PMIDs were resolved from DOIs via PubMed.

- NEW (disease/process): ARF1 is a negative regulator of cGAS-STING type I interferon signaling; heterozygous GTPase-defective ARF1 missense mutations (e.g. R99C/R99H) cause a previously unrecognized type I interferonopathy. Mechanistically mutant ARF1 perturbs mitochondrial morphology (driving mtDNA release and cGAS activation) and causes accumulation of active STING at the Golgi/ERGIC owing to defective retrograde transport — a dual role in mitochondrial integrity and STING recycling [PMID:37914730 "we identify the GTPase ADP-ribosylation factor 1 (ARF1) as a crucial negative regulator of cGAS-STING signalling"; "Heterozygous ARF1 missense mutations cause a previously unrecognized type I interferonopathy"]. This connects the existing KEEP_AS_NON_CORE `GO:0098586 cellular response to virus` annotation to a defined STING-recycling/retrograde-transport mechanism, but I am NOT changing that action — STING regulation remains a specialized, non-core context rather than the conserved core trafficking role.

- NEW (process/organelle coupling): Arf1 coordinates fatty-acid metabolism with mitochondrial homeostasis. A hyperactive Arf1 mutant decreased fatty-acid transporter/beta-oxidation enzyme expression, driving fatty-acid accumulation in lipid droplets, mitochondrial fragmentation, and reduced ATP synthesis; the role in fatty-acid metabolism is conserved in mammals and is proposed to act presumably via organelle contact sites [PMID:37400497 "Arf1 integrates metabolism into energy production by regulating fatty acid storage and utilization, and presumably organelle contact sites"]. PROVISIONAL for human annotation purposes (primary mechanism shown in yeast); recorded as expanded biology only, not used to add or change annotations.

- NEW (structural/mechanistic): Cryo-EM structure of a clathrin-INDEPENDENT AP-1:Arf1 tubular membrane coat. Myristoylated GTP-bound Arf1 recruits AP-1 to membranes and stabilizes it in an active conformation, and AP-1:Arf1 self-assembles into a tubular coat via Arf1 dimer interfaces without clathrin. HIV-1 Nef hijacks this AP-1:Arf1 coat to sequester MHC-I (AP-1:Arf1:Nef:MHC-I tubular coat), giving a structural mechanism for immune evasion; coat-contact residues are conserved across Arf isoforms and across AP-1/AP-3/AP-4 [PMID:36269825 "AP complexes can self-assemble with Arf1 into tubular coats without clathrin or other scaffolding factors"]. This refines the existing AP-1/TGN and Reactome Nef:ARF1:CD4 annotations with a defined coat-assembly mechanism but does not warrant changing any existing action.

- CONFIRMS (regulation/localization): GBF-family GEFs activate ARF1 at the cis-Golgi/ER exit sites for COPI-positive budding, whereas BIG1 activates ARF1 at the trans-Golgi/TGN for clathrin/AP-1-positive budding toward endosomes/plasma membrane (compartment-specific GEF control) [Torii 2024 J Neurochem, doi:10.1111/jnc.16141]. Consistent with the existing GBF1 (PMID:17956946) and TGN/AP-1 annotations; no change.

- CONFIRMS / PROVISIONAL (chemical biology, not annotation-relevant): NAV-2729 has a complex off-target profile inhibiting multiple ArfGEFs/ArfGAPs rather than binding ARFs directly; Brefeldin A inhibits GBF1 and BIG1/2 GEFs; a computational pipeline proposes ARF1 as a target of rabeprazole [Rosenberg 2023 JBC doi:10.1016/j.jbc.2023.102992; Chen 2023 Nat Commun doi:10.1038/s41467-023-39856-w]. Pharmacology/repurposing context only; PROVISIONAL and not used to alter annotations.

- Action on the review: added the three new primary references (PMID:37914730, PMID:37400497, PMID:36269825) to `references:` as statement-only findings (full_text_unavailable, no supporting_text since these full texts are not in the local publications cache), and added a STING/cGAS suggested question plus an interferonopathy-variant suggested experiment. No existing annotation `action` was changed; the STING and fatty-acid roles remain non-core/specialized contexts relative to the conserved Golgi/TGN trafficking function.