FAF2 (UBXD8/ETEA) review notes

UniProt: Q96CS3 (FAF2_HUMAN), 445 aa. Synonyms: ETEA, UBXD8, UBXN3B, KIAA0887.
Domain architecture: N-terminal UBA domain (12-48), UAS domain (thioredoxin-like, CDD cd02991 UAS_ETEA),
coiled-coil (275-350), C-terminal UBX domain (357-439). The UBX domain binds p97/VCP; the UBA domain binds ubiquitin.

Core biology

FAF2 is a membrane-anchored UBX-domain p97/VCP cofactor. It recruits the VCP segregase to the ER membrane
and to lipid droplets, where it functions both in ERAD substrate extraction/retrotranslocation and in
lipid-droplet / fatty-acid metabolism.

p97/VCP cofactor + UBX/UBA

PMID:18775313
- UBXD8/FAF2 is one of the 13 UBX-domain p97 cofactors; UBX binds p97, UBA binds ubiquitin conjugates.
- UniProt IntAct: VCP NbExp=16; UBAC2 NbExp=8. ComplexPortal CPX-8104 "VCP-NPL4-UFD1-FAF2 AAA ATPase complex".

ERAD

PMID:18711132
- FAF2/UBXD8 is part of the SEL1L/HRD1 ERAD dislocation complex (with SEL1L, OS9, AUP1, UBE2J1).
PMID:24215460
- Implicated in retrotranslocation/dislocation of ERAD substrates (e.g. NHK alpha-1-antitrypsin, PMID:25660456).

Lipid droplet / ATGL regulation

PMID:23297223
PMID:23297223
- FAF2 binds PNPLA2/ATGL (lipase binding), inhibits it (lipase inhibitor activity), promotes CGI-58/ABHD5 dissociation -> inhibits lipolysis, increases LD size.
- UBAC2 interaction restricts ER->LD trafficking of FAF2.
- LD localization independently confirmed by lipid-droplet proteomics PMID:14741744 (HuH7 LD fraction).

Stress granule disassembly

PMID:34739333
- On heat shock, FAF2 binds ubiquitinated G3BP1 and recruits VCP to extract G3BP1 -> stress granule disassembly. FAF2 here acts as a protein-macromolecule adaptor bridging ubiquitinated substrate to VCP.

Annotation assessment summary

• Core MF: ubiquitin binding (GO:0043130, UBA), ubiquitin protein ligase binding (GO:0031625), protein-macromolecule adaptor activity (GO:0030674) — these capture the informative p97-cofactor/adaptor function.
• Core CC: ER (GO:0005783), lipid droplet (GO:0005811), VCP-NPL4-UFD1 complex (GO:0034098).
• Core BP: ERAD pathway (GO:0036503), retrograde protein transport ER to cytosol (GO:0030970), lipid droplet organization (GO:0034389), stress granule disassembly (GO:0035617).
• lipase binding (GO:0035473) / lipase inhibitor activity (GO:0055102): specific, experimentally supported (PMID:23297223) — keep.
• Reactome extracellular region / azurophil granule lumen (neutrophil degranulation, R-HSA-6798751): bulk proteomic neutrophil-granule annotations; not the core ER/LD function — KEEP_AS_NON_CORE.
• The many bare "protein binding" (GO:0005515) IPI annotations: KEEP_AS_NON_CORE (uninformative term), though several map to informative interactions captured by specific terms.
• ATPase complex (GO:1904949) NAS / proteasomal protein catabolic process (GO:0010498) IEA: generic parents; keep non-core.
  

Falcon deep-research findings (incorporated 2026-06)

• Systematic VCP-UBXD adaptor interactome (Raman 2015) classifies FAF2/UBXD8 as a membrane-tethered p97 adaptor in ERAD/lipid-droplet homeostasis, recovering interactors AMFR, DERLIN2, AUP1, BAG6, UBAC2 plus the shared UFD1L/NPLOC4 module PMID:26389662. Added as a MEDIUM-relevance reference (PMID:26389662; DOI:10.1038/ncb3238) and id-only to the ERAD-pathway supported_by.
• All other major 2022-2025 Falcon papers were ALREADY incorporated in the completed review: Fujisawa 2022 eLife ubiquitin-threshold (PMID:35920641), Ganji 2023 ER-mito contact/lipid-saturation (PMID:36746962), Koyano 2024 basal pexophagy (PMID:39472561), Huo 2025 UBH-UBX module (PMID:41258083), and Olzmann 2013 ATGL/lipid-droplet (PMID:23297223). No new additions needed for these.
• Falcon reiterates FAF2's UBH (ubiquitin-binding helix) adjacent to UBX amplifies p97-UFD1L-NPLOC4 unfolding ~2-fold and is sufficient (with UFD1/NPLOC4) to extract membrane proteins from ER and mitochondria; FAF2-KO stabilized CD4 ~10-fold (already captured via PMID:41258083) [DOI:10.1038/s41467-025-65166-4].
• Falcon confirms FAF2/p97 suppresses basal pexophagy by extracting ubiquitylated PMP70/PEX16, preventing OPTN recruitment (already captured via PMID:39472561) [DOI:10.1038/s41467-024-53558-x].
• No new disease/substrate/localization finding for FAF2 beyond what the completed review already documents; the review was already comprehensive for the recent literature.