# VPS4A notes

## Local evidence reviewed

- `just fetch-gene human VPS4A` created the review stub, UniProt record, GOA table, and cached publications. GOA seeded 141 annotations, including ATPase activity, ESCRT/endosomal sorting, MVB-related transport, ESCRT-III disassembly, cytokinesis/midbody, nuclear envelope, viral budding, exosome, autophagy, and many generic protein-binding rows.
- `just deep-research-falcon human VPS4A` was attempted after the UMAD1 Falcon timeout resolved. Falcon timed out after 600 seconds and produced no report, so this review relies on local UniProt, GOA, cached publications, Reactome entries, and PN context.
- UniProt identifies VPS4A as an AAA-family vacuolar protein sorting ATPase with endosomal and cytokinesis roles. Its function comment states that VPS4A recognizes membrane-associated ESCRT-III assemblies and catalyzes their disassembly, redistributing ESCRT-III components to the cytoplasm for further MVB sorting [UniProt:Q9UN37, "Recognizes membrane-associated ESCRT-III assemblies and catalyzes their disassembly"; UniProt:Q9UN37, "Redistributes the ESCRT-III components to the cytoplasm for further rounds of MVB sorting."].
- The earliest mammalian endosome evidence used wild-type and ATPase-defective hVPS4. ATPase-defective mutants localized to endocytic vacuoles and produced a kinetic block in postendosomal cholesterol sorting, supporting an endosomal trafficking role but not a direct cholesterol transporter function [PMID:10637304, "The yeast vacuolar sorting protein Vps4p is an ATPase required for endosomal trafficking"; PMID:10637304, "expression of mutant hVPS4 gives rise to a kinetic block in postendosomal cholesterol sorting."].
- VPS4A/B can complement yeast vps4 defects and are involved in late endosomal protein transport; the VPS4A E228Q ATPase-domain mutant caused dominant-negative vacuolar protein sorting defects [PMID:11563910, "both human VPS4 proteins are involved in intracellular protein trafficking, presumably at a late endosomal protein transport step"].
- ATPase-deficient hVPS4 blocks formation of internal vesicles in early and late endosomal vacuoles and stabilizes bilayered clathrin coats, supporting MVB/ILV formation and coat disassembly annotations but not "endosomal vesicle fusion" [PMID:15075231, "hVPS4(EQ) leads to a reduction in the number of internal vesicles in early and late endosomal vacuoles"; PMID:15075231, "disassembly of the coat is required for the formation of internal vesicles."].
- MIT-domain structural work shows that VPS4A/VPS4B recognize ESCRT-III/CHMP MIM motifs; mutations blocking these interactions impair VPS4 recruitment, endosomal sorting, and HIV budding [PMID:17928862, "VPS4 ATPases perform a key function in this pathway by recognizing membrane-associated ESCRT-III assemblies and catalysing their disassembly"; PMID:18606141, "Mutations that block VPS4 MIT-MIM2 interactions inhibit VPS4 recruitment, lysosomal protein targeting, and HIV-1 budding."].
- Recent reconstitution/structural work supports VPS4 with CHMP2A-CHMP3 as a minimal membrane fission machinery [PMID:36604498, "VPS4 can constrict and cleave CHMP2A-CHMP3 membrane tubes"; PMID:36604498, "CHMP2A-CHMP3-VPS4 act as a minimal membrane fission machinery."].
- VPS4A/B and ESCRT-III are also required for normal cell-division contexts. Depletion of VPS4A, VPS4B, or CHMP proteins inhibited abscission and altered centrosome/spindle phenotypes; VPS4 proteins localized to spindle poles and midbodies [PMID:20616062, "depletion of VPS4A, VPS4B, or any of the 11 different human ESCRT-III (CHMP) proteins inhibited abscission"; PMID:20616062, "VPS4 proteins concentrated at spindle poles during mitosis and then at midbodies during cytokinesis"]. ANCHR/ZFYVE19 retains VPS4 at the midbody ring during abscission-checkpoint signaling [PMID:24814515, "ANCHR associates with VPS4 at the midbody ring following DNA segregation defects to control abscission timing"].
- Viral budding annotations are directly supported but are host-pathogen exploitation of the same ESCRT machinery rather than the core evolved cellular function. Dominant-negative Vps4 arrested HIV-1 and MLV budding [PMID:11595185, "Dominant negative mutant Vps4 proteins that inhibit vacuolar protein sorting also arrest HIV-1 and MLV budding."]. Ebola VP40 can redirect VPS4 and VPS4 ATPase inhibition reduced budding [PMID:17940959, "A lack of VPS4 adenosine triphosphatase activity reduced budding by up to 80%"].
- Plasma membrane repair and exosome secretion are ESCRT-output contexts that should be kept as non-core if directly supported. The plasma membrane repair paper shows rapid ESCRT recruitment to wounds and ESCRT-mediated shedding of damaged membrane [PMID:24482116, "ESCRT proteins were recruited within seconds to plasma membrane wounds"; PMID:24482116, "repair of certain wounds is ensured by ESCRT-mediated extracellular shedding of wounded portions."].
- Autophagy-related rows require caution. Some cached evidence is yeast-only or review-level: yeast VPS4 deletion impairs pAPI maturation via autophagy/Cvt [PMID:17428789, "deletion of VPS4 and VPS36 caused impaired maturation of the vacuolar proaminopeptidase I (pAPI) via autophagy or the cytosol to vacuole targeting pathway"], and a review described ESCRT-III membrane neck cleavage as "probably" important for autophagy [PMID:20588296, "ESCRT-III-mediated membrane neck cleavage is crucial for many processes, including the biogenesis of multivesicular bodies, viral budding, cytokinesis, and probably autophagy."]. PN places VPS4A in autophagophore sealing and microautophagy contexts, but the PN rows lack PMIDs and are search context only.
- The PN projection to `GO:0000815 ESCRT III complex` should not be added for VPS4A. VPS4A is the AAA ATPase that remodels/disassembles ESCRT-III assemblies, not an ESCRT-III core subunit.

## Curation synthesis

The core molecular/cellular role of VPS4A is ATP hydrolysis-driven remodeling and disassembly of ESCRT-III assemblies. This recycling/disassembly function enables ESCRT membrane remodeling at late endosomes/MVBs and other topologically equivalent membrane-neck sites. `GO:0140545 ATP-dependent protein disaggregase activity`, `GO:0016887 ATP hydrolysis activity`, `GO:1904903 ESCRT III complex disassembly`, `GO:1904896 ESCRT complex disassembly`, and endosome/MVB sorting terms are therefore central.

Plain `GO:0005515 protein binding` rows should not be retained as informative functions. Many underlying interactions are real and mechanistically important, but the better curation should point to ESCRT-III recognition/complex binding and ATP-driven complex disassembly rather than generic binding.

Cell-division, nuclear-envelope, viral budding, plasma-membrane-repair, and exosome rows are supported ESCRT-output contexts but should be marked non-core unless the individual evidence is too broad or indirect. Autophagy rows should remain conservative pending Falcon and direct human evidence review.