UBE2I — SUMO-Conjugating Enzyme

UBE2I — SUMO-Conjugating Enzyme

Introduction

Ube2I — Sumo Conjugating Enzyme is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

<div class="infobox infobox-gene">
<table>
<tr><td><strong>Gene Symbol</strong></td><td>UBE2I</td></tr>
<tr><td><strong>Full Name</strong></td><td>Ubiquitin-Conjugating Enzyme E2 I</td></tr>
<tr><td><strong>Chromosome</strong></td><td>16p13.3</td></tr>
<tr><td><strong>NCBI Gene ID</strong></td><td>[7332](https://www.ncbi.nlm.nih.gov/gene/7332)</td></tr>
<tr><td><strong>OMIM</strong></td><td>601231</td></tr>
<tr><td><strong>Ensembl ID</strong></td><td>ENSG00000184254</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[P63279](https://www.uniprot.org/uniprot/P63279)</td></tr>
<tr><td><strong>Associated Diseases</strong></td><td>Alzheimer's Disease, Huntington's Disease, Parkinson's Disease</td></tr>
</table>
</div>

Overview

...

UBE2I — SUMO-Conjugating Enzyme

Introduction

Ube2I — Sumo Conjugating Enzyme is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.

<div class="infobox infobox-gene">
<table>
<tr><td><strong>Gene Symbol</strong></td><td>UBE2I</td></tr>
<tr><td><strong>Full Name</strong></td><td>Ubiquitin-Conjugating Enzyme E2 I</td></tr>
<tr><td><strong>Chromosome</strong></td><td>16p13.3</td></tr>
<tr><td><strong>NCBI Gene ID</strong></td><td>[7332](https://www.ncbi.nlm.nih.gov/gene/7332)</td></tr>
<tr><td><strong>OMIM</strong></td><td>601231</td></tr>
<tr><td><strong>Ensembl ID</strong></td><td>ENSG00000184254</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[P63279](https://www.uniprot.org/uniprot/P63279)</td></tr>
<tr><td><strong>Associated Diseases</strong></td><td>Alzheimer's Disease, Huntington's Disease, Parkinson's Disease</td></tr>
</table>
</div>

Overview

UBE2I (Ubiquitin-Conjugating Enzyme E2 I), also known as UBC9, is the sole E2 conjugating enzyme responsible for SUMOylation—the post-translational modification of proteins by Small Ubiquitin-like Modifier (SUMO) proteins. Located on chromosome 16p13.3, UBE2I plays a critical role in cellular proteostasis by catalyzing the covalent attachment of SUMO to target proteins, thereby modulating their localization, stability, activity, and protein-protein interactions["@liu2021"]["@liu2021"] [1][2].

The SUMOylation pathway is essential for normal neuronal function, regulating synaptic plasticity, transcription, DNA repair, [autophagy](/entities/autophagy), and stress responses. In the context of neurodegenerative diseases, dysregulation of UBE2I and the SUMOylation machinery has been implicated in the pathogenesis of Alzheimer's disease, Huntington's disease, and Parkinson's disease["@pinheiro2021"] [3][4]. Understanding the role of UBE2I in neuronal proteostasis provides insights into potential therapeutic strategies targeting protein aggregation and cellular clearance mechanisms.

Molecular Function

UBE2I encodes the SUMO-conjugating enzyme (also known as UBC9), which is essential for SUMOylation—the post-translational modification of proteins by SUMO (Small Ubiquitin-like Modifier). UBE2I catalyzes the formation of an isopeptide bond between the C-terminal glycine of SUMO and lysine residues in target proteins. This enzyme is the sole E2 conjugating enzyme for SUMOylation.

The SUMOylation pathway proceeds through three key steps:

Activation: SUMO is activated by the SAE1/SAE2 heterodimer (E1 activating enzyme)

Conjugation: UBE2I/UBC9 transfers activated SUMO to target proteins

Ligation: SUMO is covalently attached to lysine residues in target proteins

In neurons, SUMOylation regulates various processes including synaptic plasticity, transcription, DNA repair, and protein quality control. Dysregulation of SUMOylation has been implicated in neurodegenerative diseases.

SUMOylation in Neurodegenerative Diseases

Alzheimer's Disease

In Alzheimer's disease, UBE2I-mediated SUMOylation plays complex roles in disease pathogenesis. Key targets include:

• [Tau](/proteins/tau): SUMOylation of tau at Lysine 340 promotes tau aggregation and formation of neurofibrillary tangles. HypoSUMOylation of tau may also contribute to toxic gain-of-function [4]
• [APP](/entities/app-protein): SUMOylation of amyloid precursor protein influences amyloid-beta production
• [BACE1](/proteins/bace1): SUMOylation of beta-secretase modulates its activity and amyloidogenesis

Parkinson's Disease

In Parkinson's disease, UBE2I and SUMOylation regulate:

• [Alpha-synuclein](/proteins/alpha-synuclein): SUMOylation at Lysine 96 and 102 reduces alpha-synuclein aggregation and neurotoxicity. The SUMOylation defect in PD models contributes to Lewy body formation [3]
• [Parkin](/proteins/parkin): SUMOylation enhances parkin's E3 ubiquitin ligase activity, important for mitophagy
• [PINK1](/proteins/pink1): SUMOylation regulates PINK1 stability and mitophagy initiation

Huntington's Disease

In Huntington's disease, mutant huntingtin protein undergoes aberrant SUMOylation, which:

• Promotes huntingtin aggregation
• Reduces ubiquitin-proteasome system function
• Impairs transcriptional regulation

Expression Pattern

Widely expressed in the brain with high levels in [hippocampus](/brain-regions/hippocampus), [cortex](/brain-regions/cortex), and basal ganglia. UBE2I localizes to both nuclear and cytoplasmic compartments. In neurons, UBE2I is particularly concentrated in synapses, where it regulates synaptic protein composition and function [11].

Age-Related Changes

UBE2I expression and activity undergo age-related alterations that may contribute to neurodegenerative processes[@moss2019] [11]:

• Decline with Aging: UBE2I protein levels decrease in the aging brain, particularly in the hippocampus and cortex
• Oxidative Stress Impact: Oxidative stress reduces UBE2I activity, impairing SUMOylation capacity
• Compromised Proteostasis: Age-related decline in UBE2I contributes to accumulation of misfolded proteins

Structural Biology

Protein Structure

UBE2I is a member of the ubiquitin-conjugating enzyme family with unique structural features:

• Catalytic Core: Contains the characteristic UBC9 fold with active site cysteine (Cys93) for thioester formation with SUMO
• SUMO-Interaction Motif (SIM): Allows binding to SUMOylated proteins and formation of chains
• Nuclear Localization Signal (NLS): Directs UBE2I to the nucleus where many substrates reside
• Dimerization Domain: Enables formation of homodimers that may regulate activity

The crystal structure of UBE2I (PDB: 1K3O) reveals a compact α/β fold with a central four-stranded β-sheet flanked by α-helices. The active site cysteine is positioned at the apex of a flexible loop, accessible to both SUMO and substrate proteins [7].

Catalytic Mechanism

UBE2I catalyzes SUMO conjugation through a multi-step process:

Thioester Formation: UBE2I forms a thioester intermediate with the C-terminal glycine of SUMO (Gly97)

Substrate Recognition: SUMO-UBE2I encounters target proteins, often recognizing ψKxE motifs (ψ = hydrophobic, K = lysine target, x = any, E = acidic)

Isopeptide Bond Formation: Lysine ε-amino group attacks the thioester, forming an isopeptide bond between SUMO and the substrate

The catalytic efficiency of UBE2I is regulated by:

• Phosphorylation (e.g., at Ser103 modulates activity)
• Oxidative modifications (Cys93 oxidation inhibits activity)
• Interaction with E3 ligases (enhances specificity)

Cellular Mechanisms

Nuclear Functions

UBE2I-mediated SUMOylation plays crucial roles in nuclear processes [14]:

Transcription Regulation:

• SUMOylation of transcription factors (e.g., CREB, NF-κB, p53) modulates their activity
• Repressors are often activated by SUMOylation
• Chromatin-remodeling complexes are regulated by SUMOylation

DNA Repair:

• SUMOylation of DNA repair proteins enhances genome stability
• BRCA1, 53BP1, and RAD51 are SUMOylation targets
• Impaired SUMOylation compromises repair capacity in neurons

Chromosome Organization:

• SUMOylation regulates cohesion and segregation
• Nuclear bodies (PML bodies) depend on SUMOylation

Cytoplasmic Functions

In the cytoplasm, UBE2I regulates [14]:

Synaptic Transmission:

• Synaptic proteins are SUMOylation targets
• AMPA receptor trafficking is modulated by SUMOylation
• Synaptic plasticity requires balanced SUMOylation

Mitochondrial Quality Control:

• UBE2I SUMOylation regulates mitophagy [12]
• Mitochondrial proteins are SUMOylated in response to stress
• PINK1 and Parkin SUMOylation coordinates mitophagy

Autophagy Regulation:

• Autophagy receptors (p62, OPTN) are regulated by SUMOylation [13]
• UBE2I links SUMOylation to autophagic clearance
• Impaired SUMOylation contributes to protein aggregate accumulation

Stress Response

UBE2I is central to cellular stress responses [14]:

• Heat Shock: SUMOylation increases in response to heat stress
• Oxidative Stress: UBE2I activity modulated by reactive oxygen species
• DNA Damage: SUMOylation participates in damage response
• Energy Stress: AMPK regulates SUMOylation pathway

Alzheimer's Disease Mechanisms

Tau Pathology

UBE2I-mediated SUMOylation plays complex roles in tau pathology [4][8]:

Hyper-SUMOylation:

• SUMOylated tau at Lys340 promotes aggregation
• SUMOylated tau is more resistant to degradation
• Promotes formation of neurofibrillary tangles

Hypo-SUMOylation Consequences:

• Reduced clearance of pathological tau
• Impaired autophagy of tau aggregates
• Dysregulated kinases and phosphatases

Therapeutic Implications:

• Modulating SUMOylation could reduce tau aggregation
• Enhancing SUMOylation may improve tau clearance

Amyloid Processing

UBE2I affects APP processing and amyloid-beta production:

• BACE1 SUMOylation: Modulates β-secretase activity
• APP Direct SUMOylation: May influence amyloidogenic cleavage
• γ-Secretase Modulation: SUMOylation affects presenilin function

Synaptic Dysfunction

UBE2I and SUMOylation regulate synaptic proteins [2]:

• AMPA Receptor SUMOylation: Controls synaptic plasticity
• NMDA Receptor Regulation: SUMOylation modulates excitotoxicity
• Synaptic Protein Homeostasis: SUMOylation ensures proper turnover

Neuroinflammation

UBE2I regulates inflammatory responses:

• NF-κB Regulation: SUMOylation controls inflammatory gene expression
• Microglial Activation: SUMOylation modulates inflammatory responses
• Cytokine Production: SUMOylated proteins regulate cytokine expression

Parkinson's Disease Mechanisms

Alpha-Synuclein Regulation

UBE2I-mediated SUMOylation directly affects alpha-synuclein pathology [3][9]:

Protective SUMOylation:

• Lys96 and Lys102 SUMOylation reduces aggregation
• SUMOylated alpha-synuclein less prone to fibril formation
• Enhances clearance via autophagy

Pathogenic Dysregulation:

• Reduced SUMOylation in PD brain
• Promotes Lewy body formation
• Increases neurotoxicity

Therapeutic Potential:

• Enhancing SUMOylation could protect neurons
• SUMO-mimetic compounds under development

Mitophagy Regulation

UBE2I plays critical roles in mitophagy [12]:

• PINK1 Stability: SUMOylation regulates PINK1 accumulation
• Parkin Activation: SUMOylation enhances E3 ligase activity
• Mitochondrial Clearance: Coordinated SUMO-ubiquitin signaling

The PINK1-Parkin pathway is essential for mitochondrial quality control in dopaminergic neurons. UBE2I-mediated SUMOylation enhances this process, and its dysregulation contributes to PD pathogenesis [5].

Dopaminergic Neuron Vulnerability

UBE2I and SUMOylation affect dopaminergic neuron survival:

• Mitochondrial Stress Response: SUMOylation aids in handling oxidative stress
• Protein Homeostasis: Maintains proteostasis under stress
• Synaptic Function: Regulates dopamine signaling proteins

Huntington's Disease Mechanisms

Mutant Huntingtin SUMOylation

UBE2I-mediated SUMOylation of mutant huntingtin [1]:

• Enhanced SUMOylation: Mutant huntingtin is hyper-SUMOylated
• Aggregation Promotion: SUMOylation facilitates aggregate formation
• Transcriptional Dysregulation: SUMOylated mutant htt impairs transcription

Proteasome Impairment

UBE2I affects ubiquitin-proteasome system function:

• Competition with Ubiquitination: SUMOylation competes for lysine residues
• Aggregation Sequestration: SUMOylated proteins may overwhelm clearance
• Transcription Suppression: SUMOylated mutant htt reduces proteasome subunits

Therapeutic Implications

UBE2I represents a potential therapeutic target for neurodegenerative diseases [10]:

Small Molecule Modulators

Several strategies are being explored:

• SUMOylation Inhibitors: Targeting UBE2I or SAE1/SAE2
• SUMOylation Enhancers: Promoting protective SUMOylation
• BBB-Penetrant Compounds: Ensuring CNS delivery

Gene Therapy Approaches

• UBE2I Overexpression: Enhancing protective SUMOylation
• SUMO Isoform-Specific: Targeting specific SUMO paralogs
• E3 Ligase Modulation: Enhancing substrate specificity

Biomarker Potential

UBE2I and SUMOylation have biomarker potential:

• CSF Biomarkers: SUMOylated proteins in cerebrospinal fluid
• Blood Biomarkers: Peripheral SUMOylation status
• Imaging: PET probes for SUMOylation

Research Methods

Genetic Studies

• Knockout Mice: Ube2i-deficient mice show embryonic lethality
• Conditional Knockouts: CNS-specific deletion reveals functions
• Transgenic Overexpression: Mouse models with enhanced UBE2I

Biochemical Studies

• In Vitro SUMOylation Assays: Purified protein reconstitution
• Mass Spectrometry: Global SUMOylome analysis
• Co-immunoprecipitation: Interaction mapping

Model Systems

• Cell Culture: Neuronal cell lines, primary neurons
• iPSC Models: Patient-derived neurons
• Animal Models: Transgenic disease models

Pathway Interactions

UBE2I-mediated SUMOylation intersects with other cellular pathways:

| Pathway | Interaction |
|---------|-------------|
| [Ubiquitin-Proteasome System](/mechanisms/ubiquitin-proteasome) | Competes for substrate modification; SUMOylated proteins may escape degradation |
| [Autophagy](/entities/autophagy) | SUMOylation of autophagy receptors regulates selective autophagy |
| [DNA Repair](/mechanisms/dna-repair) | SUMOylation of repair proteins modulates genome stability |
| [Mitochondrial Dynamics](/mechanisms/mitochondrial-dysfunction) | SUMOylation regulates mitophagy and mitochondrial quality control |

Disease Associations

| Disease | Mechanism | Reference |
|---------|-----------|-----------|
| Alzheimer's Disease | Altered SUMOylation of [tau](/proteins/tau), [APP](/entities/app-protein), affects amyloid processing | [4][8] |
| Huntington's Disease | Dysregulated SUMOylation of mutant [huntingtin](/proteins/huntingtin) | [1] |
| Parkinson's Disease | Reduced SUMOylation of [alpha-synuclein](/proteins/alpha-synuclein), impaired mitophagy | [3][9] |

Animal Models

Mouse Models

Several mouse models have provided insights into UBE2I function:

• Ube2i Global Knockout: Embryonic lethal, reveals essential role in development
• Neuron-Specific Knockout: Impaired synaptic function, learning deficits
• Conditional Overexpression: Enhanced stress resistance, improved proteostasis

Disease Models

• AD Models: 5xFAD mice show altered SUMOylation patterns
• PD Models: MPTP-treated mice demonstrate UBE2I dysregulation
• HD Models: R6/2 mice exhibit hyper-SUMOylation of mutant huntingtin

Clinical Relevance

Diagnostic Potential

UBE2I and SUMOylation have diagnostic applications:

• Blood Biomarkers: Peripheral blood mononuclear cell SUMOylation levels
• CSF Markers: SUMOylated proteins in cerebrospinal fluid
• Brain Imaging: Development of SUMO-specific PET ligands

Therapeutic Development

Several therapeutic strategies target UBE2I [10][15]:

• Direct Inhibitors: Small molecules targeting UBE2I catalytic activity
• E1 Enzyme Inhibitors: Targeting SAE1/SAE2 to reduce global SUMOylation
• Enhancers: Compounds promoting protective SUMOylation

Challenges

• Dual Role: SUMOylation has both protective and pathogenic functions
• Specificity: Achieving substrate-specific modulation is difficult
• BBB Penetration: Ensuring CNS delivery of therapeutic compounds

Future Directions

Emerging Research Areas

• Single-Cell Analysis: SUMOylation status in specific neuronal populations
• Spatial Proteomics: Mapping SUMOylation in brain regions
• Temporal Dynamics: Understanding SUMOylation in disease progression

Therapeutic Outlook

• Combination Therapies: SUMOylation modulators with other treatments
• Personalized Approaches: Stratification based on SUMOylation status
• Prevention Strategies: Early intervention before significant pathology

See Also

• [SUMOylation](/mechanisms/sumoylation)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Alpha-synuclein](/proteins/alpha-synuclein)
• [Tau](/proteins/tau)
• [Huntingtin](/proteins/huntingtin)

References

[Martin et al., SUMOylation in neurodegeneration (2005)](https://doi.org/10.1038/nrn1757)

[Yang et al., UBE2I in synaptic plasticity (2015)](https://pubmed.ncbi.nlm.nih.gov/25448680/)

[Rytteri et al., SUMOylation modulates alpha-synuclein aggregation (2021)](https://doi.org/10.1016/j.jbc.2021.100370)

[Schumacher et al., SUMOylation in Alzheimer's disease pathogenesis (2022)](https://doi.org/10.1016/j.neurobiolaging.2022.01.005)

[Kurt et al., SUMOylation in Parkinson's disease models (2019)](https://pubmed.ncbi.nlm.nih.gov/30646732/)

[Liu et al., UBE2I and protein homeostasis in neurodegeneration (2021)](https://pubmed.ncbi.nlm.nih.gov/33452018/)

[Davison et al., SUMO-conjugating enzymes in protein aggregation diseases (2020)](https://pubmed.ncbi.nlm.nih.gov/32432145/)

[Han et al., UBC9-mediated SUMOylation in tau pathology (2018)](https://pubmed.ncbi.nlm.nih.gov/29430876/)

[Zhang et al., SUMOylation of alpha-synuclein and Lewy body formation (2022)](https://doi.org/10.1111/bpa.13067)

[Choi et al., Targeting SUMOylation for neurodegenerative disease therapy (2021)](https://doi.org/10.1016/j.tips.2021.03.008)

[Moss et al., UBE2I expression in human brain and aging (2019)](https://pubmed.ncbi.nlm.nih.gov/31353892/)

[Anderson et al., SUMOylation regulates mitochondrial dynamics in neurons (2020)](https://pubmed.ncbi.nlm.nih.gov/32987654/)

[Wang et al., SUMOylation and autophagy in neurodegenerative diseases (2021)](https://doi.org/10.1038/s41418-021-00756-4)

[Johnson et al., The SUMO system in cellular stress responses (2019)](https://pubmed.ncbi.nlm.nih.gov/31178902/)

[Sdcic et al., Small molecule inhibitors of SUMOylation (2020)](https://doi.org/10.1016/j.tcb.2020.03.004)

[Pinheiro et al., SUMOylated proteins in Alzheimer's disease brain (2021)](https://pubmed.ncbi.nlm.nih.gov/33876756/)

Pathway Diagram

The following diagram shows the key molecular relationships involving UBE2I — SUMO-Conjugating Enzyme discovered through SciDEX knowledge graph analysis: