# CHMP4A notes

## Local evidence reviewed

- `just fetch-gene human CHMP4A` created the review stub, UniProt record, GOA table, cached publications, Reactome entries, and PANTHER family data. GOA seeded 103 annotations covering ESCRT-III complex membership, MVB/endosomal sorting, membrane budding/fission/polymerization, autophagy, plasma membrane repair, viral budding, cytokinesis/midbody, nuclear envelope/nuclear pore contexts, broad locations, and generic binding rows.
- `just deep-research-falcon human CHMP4A` timed out after 600 seconds on 2026-06-02 and did not produce a Falcon report.
- UniProt identifies CHMP4A as a probable core ESCRT-III component involved in MVB formation and sorting of endosomal cargo into MVB intraluminal vesicles [UniProt:Q9BY43, "Probable core component of the endosomal sorting required for transport complex III (ESCRT-III)"; UniProt:Q9BY43, "involved in multivesicular bodies (MVBs) formation and sorting of endosomal cargo proteins into MVBs"]. UniProt also states that ESCRT-III proteins mediate membrane fission together with VPS4 and that CHMP4A/B/C are required for exosomal release of SDCBP, CD63, and syndecan [UniProt:Q9BY43, "believed to mediate the necessary vesicle extrusion and/or membrane fission activities"; UniProt:Q9BY43, "CHMP4A/B/C are required for the exosomal release of SDCBP, CD63 and syndecan"].
- The strongest direct mechanistic evidence comes from the hSnf7 filament paper. It reports that hSnf7-1/CHMP4A and hSnf7-2/CHMP4B form ESCRT-III polymers, target to endosomes and plasma membrane when overexpressed, and assemble into curved filaments that promote outward membrane budding [PMID:18209100, "proteins hSnf7-1 (CHMP4A) and hSnf7-2 (CHMP4B)"; PMID:18209100, "assemble into regular approximately 5-nm filaments that curve and self-associate"; PMID:18209100, "form novel membrane-attached filaments that can promote or stabilize negative curvature and outward budding"].
- MVB and membrane-scission annotations are well supported by the same hSnf7 work and ESCRT scission literature. The authors propose that ESCRT-III polymers delineate and help generate MVB luminal vesicles [PMID:18209100, "ESCRT-III polymers delineate and help generate the luminal vesicles of multivesicular bodies"], and a minimal ESCRT-III reconstitution paper shows ESCRT-III has intrinsic membrane-neck scission activity [PMID:19234443, "ESCRT-III has the instrinsic ability to drive the scission of membrane necks"].
- Autophagy/autophagosome annotations should be retained in the PN context but should not be overinterpreted as a CHMP4A-specific phagophore-closure assay unless directly supported. The older autophagy paper tested ESCRT depletion and hVps24/CHMP3 rather than CHMP4A directly [PMID:17984323, "Functional multivesicular bodies are required for autophagic clearance"], but the human neuron paper directly reports that hSnf7-1/CHMP4A knockdown causes autophagosome accumulation [PMID:21975012, "SiRNA knockdown of hSnf7-1 in human neurons leads to autophagosome accumulation"].
- The neuron paper supports CHMP4A-dependent endosomal cargo turnover and neuronal survival as non-core phenotypic/context annotations [PMID:21975012, "hSnf7-1 and hSnf7-2 are required for the survival of human neurons"; PMID:21975012, "hSnf7-1 and hSnf7-2 may have preferred interacting partners to form distinct ESCRT-III with different cellular functions"]. It does not support the seeded `post-translational protein targeting to endoplasmic reticulum membrane` row, which should be removed.
- Plasma membrane repair is a valid ESCRT output context but not the core endolysosomal proteostasis function. The cached repair paper reports rapid ESCRT recruitment to wounds and repair by extracellular 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"].
- Nuclear envelope/nuclear pore and cytokinesis annotations are valid non-core ESCRT contexts. The nuclear envelope paper supports ESCRT-III control of nuclear envelope reformation [PMID:26040713, "ESCRT-III controls nuclear envelope reformation"], and the cytokinesis paper places CHMP4/Snf7 proteins at the midbody and in abscission regulation [PMID:22724069, "Borealin interacts directly with the Snf7 components of ESCRT-III"; PMID:22724069, "controls abscission timing through inhibition of ESCRT-III Snf7 polymerization"].
- Viral budding annotations are directly supported but are host-pathogen hijacking contexts, not core endogenous function. The ALIX-CHMP4 structure paper says ALIX must recruit CHMP4 subunits to promote HIV budding and cytokinesis [PMID:18511562, "ALIX protein must bind and recruit CHMP4 subunits of the ESCRT-III complex"], and cellular ESCRT-III spiral work relates CHMP4A-containing spirals to HIV budding [PMID:24878737, "Structure of cellular ESCRT-III spirals and their relationship to HIV budding"].
- Generic `GO:0005515 protein binding` rows should be marked over-annotated. CHMP4A has real interactions with PDCD6IP/ALIX, CHMP2A, CHMP3, CHMP4 paralogs, CHMP6, VPS4, Borealin, and high-throughput interactors, but the informative curation is ESCRT-III polymerization/membrane fission and specific complex contexts, not plain protein binding.

## Curation synthesis

The core CHMP4A role is non-enzymatic ESCRT-III structural subunit activity: CHMP4A/Snf7 polymerizes on endosomal/MVB and related membranes, forms curved membrane-associated filaments/rings, and supports reverse-topology membrane remodeling, budding, and fission. Core annotations should include ESCRT III complex, MVB sorting/assembly, late endosome/MVB/endosomal membrane locations, protein polymerization, vesicle budding from membrane, membrane fission, and ubiquitin-dependent cargo degradation through the MVB pathway.

Autophagy/autophagosome annotations are PN-relevant and supported by CHMP4A knockdown in human neurons plus broader ESCRT/MVB autophagy evidence, but the review should avoid claiming that CHMP4A alone has been directly assayed as the phagophore-sealing effector in the cached literature. Cytokinesis, nuclear envelope sealing, plasma membrane repair, viral budding, and neuronal survival/cargo-turnover rows should be kept as non-core ESCRT output contexts where directly supported. Generic protein-binding rows and the unsupported ER-targeting process should not be retained as informative CHMP4A functions.