HUWE1 Protein
<div class="infobox infobox-protein">
| | |
|---|---|
| Protein Name | HUWE1 (MULE/ARF-BP1) |
| Gene | [HUWE1](/genes/huwe1) |
| UniProt | [Q7Z6Z7](https://www.uniprot.org/uniprot/Q7Z6Z7) |
| Molecular Weight | ~482 kDa |
| Length | 4,374 amino acids |
| Subcellular Localization | Cytoplasm, nucleus, mitochondria-associated |
| Protein Family | HECT-domain E3 ubiquitin ligases |
</div>
Overview
HUWE1 is one of the largest human proteins and a HECT-domain E3 ubiquitin ligase that catalyzes polyubiquitination of a broad substrate repertoire controlling [apoptosis](/entities/apoptosis), DNA repair, mitochondrial dynamics, and protein quality control. In [neurons](/entities/neurons), HUWE1 functions as a master proteostasis regulator, ubiquitinating misfolded proteins for proteasomal degradation, controlling mitochondrial fusion-fission balance through [MFN2](/genes/mfn2) ubiquitination, and modulating apoptosis through [MCL-1](/proteins/mcl1-protein) and p53 regulation. Loss-of-function mutations cause X-linked intellectual disability, and HUWE1 dysfunction contributes to neurodegeneration[@zhong2005].
Structure
...HUWE1 Protein
<div class="infobox infobox-protein">
| | |
|---|---|
| Protein Name | HUWE1 (MULE/ARF-BP1) |
| Gene | [HUWE1](/genes/huwe1) |
| UniProt | [Q7Z6Z7](https://www.uniprot.org/uniprot/Q7Z6Z7) |
| Molecular Weight | ~482 kDa |
| Length | 4,374 amino acids |
| Subcellular Localization | Cytoplasm, nucleus, mitochondria-associated |
| Protein Family | HECT-domain E3 ubiquitin ligases |
</div>
Overview
HUWE1 is one of the largest human proteins and a HECT-domain E3 ubiquitin ligase that catalyzes polyubiquitination of a broad substrate repertoire controlling [apoptosis](/entities/apoptosis), DNA repair, mitochondrial dynamics, and protein quality control. In [neurons](/entities/neurons), HUWE1 functions as a master proteostasis regulator, ubiquitinating misfolded proteins for proteasomal degradation, controlling mitochondrial fusion-fission balance through [MFN2](/genes/mfn2) ubiquitination, and modulating apoptosis through [MCL-1](/proteins/mcl1-protein) and p53 regulation. Loss-of-function mutations cause X-linked intellectual disability, and HUWE1 dysfunction contributes to neurodegeneration[@zhong2005].
Structure
HUWE1 contains multiple functional domains across its massive polypeptide chain. The N-terminal region contains ARM/HEAT repeats for substrate recognition and protein-protein interactions. The UBA (ubiquitin-associated) domain recognizes ubiquitinated substrates. The WWE domain mediates protein-protein interactions involved in ubiquitin signaling. The BH3 (BCL-2 homology 3) domain directly binds MCL-1 for targeted ubiquitination. The C-terminal HECT (Homologous to E6-AP C-Terminus) domain contains the catalytic cysteine that accepts ubiquitin from E2 conjugating enzymes and transfers it to substrates[@chen2005].
The HECT domain forms a bilobed structure: the N-lobe binds the E2 enzyme (primarily UbcH5/UBE2D family), while the C-lobe contains the catalytic cysteine (Cys4341) that forms a thioester intermediate with ubiquitin before transfer to the substrate lysine.
Normal Function
Protein Quality Control
HUWE1 ubiquitinates misfolded and aggregation-prone proteins, generating K48-linked polyubiquitin chains that target them for proteasomal degradation. This activity prevents protein aggregation in neurons, which are post-mitotic and cannot dilute toxic aggregates through cell division[@zhao2008].
Mitochondrial Dynamics
HUWE1 ubiquitinates [MFN2](/genes/mfn2) (mitofusin-2), promoting mitochondrial fission under stress conditions. This is coordinated with [PINK1](/genes/pink1)/[Parkin](/genes/prkn) mitophagy: HUWE1-mediated MFN2 degradation on damaged mitochondria prevents their re-fusion with the healthy network, facilitating selective removal by mitophagy[@leboucher2012].
Apoptosis Regulation
Through ubiquitination and degradation of the anti-apoptotic protein [MCL-1](/proteins/mcl1-protein), HUWE1 lowers the apoptotic threshold. HUWE1 also degrades p53 (as ARF-BP1), and the balance between these activities determines neuronal survival versus death decisions under stress[@zhong2005].
Role in Disease
Neurodegeneration
HUWE1 dysfunction in [Alzheimer's](/diseases/alzheimers-disease) and [Parkinson's](/diseases/parkinsons-disease) disease leads to impaired clearance of misfolded [tau](/proteins/tau) and [alpha-synuclein](/proteins/alpha-synuclein), mitochondrial network fragmentation from dysregulated MFN2 ubiquitination, and aberrant apoptosis from MCL-1/p53 imbalance[@gong2021].
X-Linked Intellectual Disability
Mutations in HUWE1 cause Turner type, Juberg-Marsidi, and Brooks syndromes, confirming HUWE1's essential role in brain development[@friez2016].
Therapeutic Targeting
Approaches include enhancing HUWE1 catalytic activity to boost aggregate clearance, substrate-specific modulation of HUWE1-mediated ubiquitination, and targeting the MCL-1/p53 axis to optimize neuronal survival thresholds.
See Also
- [HUWE1 Gene](/genes/huwe1)
- [MARCH5 Protein](/proteins/march5-protein) — mitochondrial E3 ligase
- [Ubiquitin-Proteasome Dysfunction](/mechanisms/ubiquitin-proteasome-dysfunction)
- [Mitochondrial Dysfunction in Neurodegeneration](/mechanisms/mitochondrial-dysfunction-neurodegeneration)
External Links
- [UniProt: Q7Z6Z7](https://www.uniprot.org/uniprot/Q7Z6Z7)
- [InterPro: HUWE1](https://www.ebi.ac.uk/interpro/protein/UniProt/Q7Z6Z7/)
References
[Zhong Q et al, Mule/ARF-BP1, a BH3-only E3 ubiquitin ligase, catalyzes the polyubiquitination of Mcl-1 and regulates apoptosis (2005)](https://pubmed.ncbi.nlm.nih.gov/15620353/)
[Chen D et al, ARF-BP1/Mule is a critical mediator of the ARF tumor suppressor (2005)](https://pubmed.ncbi.nlm.nih.gov/15620354/)
[Zhao X et al, The HECT-domain ubiquitin ligase Huwe1 controls neural differentiation and proliferation by destabilizing the N-Myc oncoprotein (2008)](https://pubmed.ncbi.nlm.nih.gov/18316603/)
[Leboucher GP et al, Stress-induced phosphorylation and proteasomal degradation of mitofusin 2 facilitates mitochondrial fragmentation and apoptosis (2012)](https://pubmed.ncbi.nlm.nih.gov/22841712/)
[Gong Y et al, Ubiquitin ligase HUWE1 regulates neuronal proteostasis (2021)](https://pubmed.ncbi.nlm.nih.gov/34088912/)
[Friez MJ et al, HUWE1 mutations in Juberg-Marsidi and Brooks syndromes: the results of an X-chromosome exome sequencing study (2016)](https://pubmed.ncbi.nlm.nih.gov/27030131/)