# CHMP5 notes

## Working synthesis

CHMP5 (UniProt Q9NZZ3) is a SNF7/ESCRT-III family protein best treated as an ESCRT-III regulatory component for endosomal MVB sorting and VPS4/LIP5-mediated ESCRT-III recycling. UniProt describes CHMP5 as a "Probable peripherally associated component" of ESCRT-III involved in MVB formation and sorting of endosomal cargo into MVBs, with ILVs delivered to lysosomes for degradation of membrane proteins such as stimulated growth factor receptors [UniProt:Q9NZZ3 "involved in multivesicular bodies (MVBs) formation and sorting of endosomal cargo proteins into MVBs"; UniProt:Q9NZZ3 "enabling degradation of membrane proteins, such as stimulated growth factor receptors"].

The most direct CHMP5-specific cellular evidence is Ward et al. 2005: CHMP5 is a LIP5-binding protein, is mainly cytosolic, and CHMP5 RNAi reduces EGFR degradation without grossly disrupting early endosomes, lysosomes, or Golgi. That paper concludes that LIP5 and CHMP5 function in MVB sorting, while only LIP5 is required for HIV release [PMID:15644320 "We identify CHMP5 as a LIP5-binding protein and show that CHMP5 is primarily cytosolic."; PMID:15644320 "CHMP5 depletion results in an increase in the release of infectious HIV-1 particles."; PMID:15644320 "both LIP5 and CHMP5 function in MVB sorting, whereas only LIP5 is required for HIV release."].

The mechanistic refinement is that CHMP5 binds LIP5/VTA1 and helps regulate VPS4 activation/disassembly of ESCRT-III rather than acting as a CHMP4/Snf7-like primary filament/scission subunit. Shim et al. 2008 confirm high-affinity LIP5-CHMP5 binding and suggest CHMP5-bound LIP5 may regulate engagement of other ESCRT-III proteins and VPS4 [PMID:18385515 "LIP5 binds preferentially to soluble CHMP5"; PMID:18385515 "CHMP5 bound to LIP5 might negatively regulate LIP5 for engagement with other ESCRT-III proteins and VPS4"]. Skalicky et al. 2012 show that LIP5 binds a novel MIM element in CHMP5, and that stable VPS4 complexes with LIP5 and CHMP5 require LIP5 to bind both a MIM1-containing ESCRT-III protein and CHMP5 [PMID:23105106 "the second LIP5 MIT module binds with unusually high affinity to a novel MIM element within the ESCRT-III protein CHMP5"; PMID:23105106 "promoting assembly of active VPS4 enzymes on the polymeric ESCRT-III substrate"].

Proteostasis-network context: CHMP5 supports endolysosomal degradation through ESCRT/MVB sorting, so MVB sorting, MVB assembly, ubiquitin-dependent protein catabolism via MVB sorting, late endosome-to-lysosome transport, and ESCRT-III disassembly are core or near-core PN-relevant terms. General ESCRT autophagy literature shows that functional MVBs are required for autophagic clearance of aggregate-prone proteins, but the cached CHMP5 GOA autophagy annotations mostly derive from ESCRT-complex context rather than CHMP5-specific autophagosome sealing assays [PMID:17984323 "Functional multivesicular bodies are required for autophagic clearance"; PMID:17984323 "functional MVBs are required to prevent accumulation of abnormal proteins"]. A Shigella infection study provides CHMP5-specific anti-bacterial autophagy evidence, but it is infection context: IcsB modifies CHMP5 and CHMP5 knockout affects S. flexneri escape from host autophagy [PMID:30061757 "CHMP5-one of the IcsB targets and a component of the ESCRT-III complex-specifically affected S. flexneri escape from host autophagy."].

Secondary ESCRT contexts should generally be kept as non-core. Broad ESCRT-III papers support roles in cytokinetic abscission, centrosome/spindle maintenance, nuclear envelope sealing, plasma membrane repair, and viral budding, but they should not override the CHMP5-specific MVB/VPS4-LIP5 regulatory function [PMID:20616062 "depletion of VPS4A, VPS4B, or any of the 11 different human ESCRT-III (CHMP) proteins inhibited abscission"; PMID:26040713 "ESCRT-III controls nuclear envelope reformation"; PMID:24482116 "repair of certain wounds is ensured by ESCRT-mediated extracellular shedding of wounded portions"].

The NOD2/LPS/MDP annotations are not core CHMP5 function. Thiebaut et al. identify CHMP5 as a NOD2-interacting protein and report induction by MDP/LPS, but the study itself says these new interacting proteins did not appear to be major NOD2-dependent NF-kappaB regulators in the assay [PMID:27812135 "the primary interaction was confirmed by coimmunoprecipitation and/or bioluminescence resonance energy transfer (BRET) experiments for 11 of these proteins"; PMID:27812135 "none of the NIPs isolated here, except RICK, appear to be major regulators of the NOD2 dependent NF-kappaB pathway"].

## Curation decisions

- Core: ESCRT-III complex membership, MVB sorting/assembly, ubiquitin-dependent cargo degradation through MVB sorting, ESCRT-III disassembly/recycling via LIP5/VTA1 and VPS4, and the endolysosomal degradation route that follows MVB sorting.
- Non-core: cytosol/nucleus/exosome locations, midbody/cytokinesis, spindle/centrosome, nuclear envelope/pore reassembly, plasma membrane repair, infection/autophagy contexts, and viral budding.
- Over-annotated: generic protein binding, cadherin binding, viral budding as a CHMP5 function, and LPS/MDP response terms inferred from induction or interaction context rather than a demonstrated CHMP5 response function.
- Modify: vacuolar transport and vesicle fusion/MVB-lysosome fusion terms should be represented as MVB sorting or late endosome-to-lysosome transport.

## Deep research status

`just deep-research-falcon human CHMP5` timed out after 600 seconds and reported that all providers failed. No `CHMP5-deep-research-falcon.md` file was written, so this review is based on UniProt, GOA-seeded annotations, cached publications, and the local synthesis above.

## Description cleanup note

The YAML `description` field was revised to keep it as a standalone biological summary. Project-specific curation framing moved here instead.

- Moved out of the YAML description: the Proteostasis Network framing interpreted CHMP5 as an endolysosomal cargo-sorting and ESCRT-recycling component, with broader ESCRT contexts treated as secondary.