CHMP1B Annotation Review Notes

Gene Overview

CHMP1B (Charged Multivesicular Body Protein 1B) is an ESCRT-III complex component with multiple cellular roles.

Core Functions (from deep research)

1. ESCRT-III component for MVB formation and ILV biogenesis - mediates reverse-topology membrane scission for cargo sorting to lysosomes
2. Normal-topology membrane scission (with IST1 partner) - mediates endosomal recycling (transferrin receptor, M6PR)
3. Cytokinetic abscission - recruits spastin to midbody for final cell division step
4. Plasma membrane repair - ESCRT machinery recruited to membrane wounds
5. Viral budding - HIV-1 release (moderate role, less essential than CHMP2/CHMP4)
6. Autophagy - required for autophagosome maturation and fusion with lysosomes

Key Evidence

• Peripherally associated ESCRT-III component [UniProt Q7LBR1]
• Forms IST1-CHMP1B copolymers for normal-topology scission [deep research]
• Interacts with VPS4 ATPases for ESCRT-III disassembly
• Interacts with spastin MIT domain for midbody recruitment PMID:18997780
• Required for EGFR degradation, regulated by USP8-mediated ubiquitination
• Localizes to: late endosomes, MVB membranes, midbodies, autophagosomes

Annotation Review Strategy

1. ACCEPT: Core ESCRT-III functions with strong experimental evidence
2. MODIFY: Terms that are too general or need specificity
3. KEEP_AS_NON_CORE: Pleiotropic/secondary functions with decent evidence
4. REMOVE/MARK_AS_OVER_ANNOTATED: Weak IEA annotations, especially those without strong lit support
5. Avoid "protein binding" - not informative, replace with specific MF terms

Key Papers to Reference

• PMID:17984323 - Autophagy, MVB function in protein aggregates
• PMID:20616062 - Centrosome and spindle maintenance, cytokinesis
• PMID:24482116 - Plasma membrane repair
• PMID:26040712 - Spastin recruitment, spindle disassembly
• PMID:26040713 - Nuclear envelope reformation
• PMID:24878737 - ESCRT-III structure, HIV budding
• PMID:16554368 - MVB sorting, EGFR degradation

REVIEW COMPLETED - Summary

Date: 2025-11-23
Status: COMPLETE

Summary Statistics

• Total annotations reviewed: 117
• ACCEPT: 66 annotations (core ESCRT-III functions)
• KEEP_AS_NON_CORE: 17 annotations (mitotic/kinetochore functions)
• MODIFY: 10 annotations (terms needing replacement)
• REMOVE: 4 annotations (extracellular exosome contaminants, inappropriate yeast terms)

Key Decisions

1. Accepted core functions:
2. MVB/late endosome localization and membrane remodeling
3. Autophagosome maturation and lysosome transport
4. Midbody abscission and nuclear envelope reformation
5. Plasma membrane repair
6. Cargo sorting via MVB pathway
7. MIT domain binding (highly specific MF)

8. Identical protein binding (ESCRT-III oligomerization)

9. Non-core but valid functions:

10. Kinetochore/mitotic functions (chromosome alignment, spindle regulation)
11. Centrosome duplication regulation

12. HIV-1 budding (moderate contributor)

13. Modified annotations:

14. Replaced generic "protein transport" with specific MVB sorting terms
15. Replaced yeast-specific "vacuole" terms with mammalian "lysosome" terms

16. Recommended replacing generic "protein binding" IPIs with specific binding terms

17. Removed annotations:

18. 3x extracellular exosome (HDA) - likely ESCRT contamination in proteomics
19. Vacuolar transport (yeast IEA) - inappropriate for human

Core Molecular Functions Identified

• GO:0090541 (MIT domain binding): High-affinity binding to VPS4 and spastin for ESCRT-III regulation
• GO:0042802 (identical protein binding): Self-assembly into helical filaments for membrane constriction

Notable Insights

• CHMP1B exhibits dual topology specificity - unique among ESCRT-III proteins
• Forms IST1-CHMP1B copolymers specifically for normal-topology scission
• Regulated by USP8-mediated deubiquitination in response to growth factors
• Bifunctional MIM motif enables context-dependent VPS4 vs spastin recruitment