PARK2 Protein - Parkin

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Parkin Protein — PARK2 E3 Ubiquitin Protein Ligase

<div class="infobox infobox-protein">
<table>
<tr><th colspan="2" style="background:#e8f4ea; text-align:center; font-size:1.1em;">PARKIN Protein</th></tr>
<tr><td><strong>Gene</strong></td><td>[PARK2](/genes/park2)</td></tr>
<tr><td><strong>Full Name</strong></td><td>Parkin RBR E3 Ubiquitin Protein Ligase</td></tr>
<tr><td><strong>UniProt ID</strong></td><td>[O60260](https://www.uniprot.org/uniprot/O60260)</td></tr>
<tr><td><strong>PDB Structure IDs</strong></td><td>1MG8, 1N4M, 2JMO, 4K7D, 5CAW</td></tr>
<tr><td><strong>Molecular Weight</strong></td><td>51.5 kDa (465 aa)</td></tr>
<tr><td><strong>Subcellular Localization</strong></td><td>Cytoplasm, Mitochondria outer membrane</td></tr>
<tr><td><strong>Protein Family</strong></td><td>RING-between-RING (RBR) family</td></tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">ALZHEIMER</a>, <a href="/wiki/alzheimer's" style="color:#ef9a9a">ALZHEIMER'S</a>, <a href="/wiki/alzheimer's-disease" style="color:#ef9a9a">ALZHEIMER'S DISEASE</a>, <a href="/wiki/amyloid" style="color:#ef9a9a">AMYLOID</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">2117 edges</a></td>
</tr>
</table>
</div>

Overview

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Parkin Protein — PARK2 E3 Ubiquitin Protein Ligase

Overview

Parkin is an E3 ubiquitin ligase encoded by the [PARK2](/genes/park2) gene, one of the most frequently mutated genes in early-onset autosomal recessive Parkinson's disease[@lcking2000]. Parkin plays a critical role in mitochondrial quality control through the regulation of mitophagy—the selective degradation of damaged mitochondria[@pickrell2015]. The PINK1-Parkin pathway is one of the best-characterized mechanisms linking mitochondrial dysfunction to neurodegeneration in Parkinson's disease.

Structure

Parkin has a complex multi-domain architecture characteristic of the RING-between-RING (RBR) family of E3 ubiquitin ligases:

Mermaid diagram (expand to render)

Key Structural Features

| Domain | Amino Acids | Function | Clinical Significance |
|--------|-------------|----------|----------------------|
| Ubl Domain | 1-76 | Phosphorylation by PINK1, ubiquitin binding | Phosphorylation site Ser65 is disease-relevant |
| RING0 | 77-165 | Structural domain, interacts with RING1 | Mutations disrupt E3 activity |
| RING1 | 212-286 | E2 binding, ubiquitin transfer | Core catalytic component |
| IBR Domain | 327-416 | In-between-RING,桥梁作用 | Mutations cause loss of function |
| RING2 | 418-465 | Catalytic cysteine, thioester formation | Catalytic core for ubiquitination |

Parkin exists in an auto-inhibited conformation in the cytosol. Activation requires phosphorylation by PINK1 and binding to phosphorylated ubiquitin, which induces dramatic conformational changes that reposition the RING domains for catalytic activity[@riley2014].

Normal Physiological Function

Mitochondrial Quality Control

Parkin's primary function is in mitochondrial quality control through mitophagy:

Mitochondrial Damage Sensing: Upon mitochondrial damage (e.g., oxidative stress, depolarization), PINK1 accumulates on the outer mitochondrial membrane[@narendra2008].

Parkin Activation: PINK1 phosphorylates ubiquitin and Parkin's Ubl domain at Ser65. This phosphorylation triggers conformational changes that activate Parkin's E3 ligase activity[@koyano2014].

Substrate Ubiquitination: Activated Parkin ubiquitinates numerous mitochondrial outer membrane proteins, including VDAC1, Mfn1/2, and TOM complex components[@chan2011].

Autophagic Clearance: Ubiquitinated mitochondria are recognized by autophagic receptors (p62/SQSTM1, OPTN, NDP52) that recruit LC3-positive autophagosomes, leading to mitochondrial degradation[@lazarou2015].

Additional Cellular Functions

Regulation of mitochondrial dynamics: Controls mitochondrial fusion/fission balance through ubiquitination of fusion proteins
Transcriptional regulation: Modulates expression of PGC-1α and mitochondrial biogenesis genes
Apoptosis regulation: Controls pro-apoptotic proteins through ubiquitination
Iron metabolism: Regulates iron homeostasis through ferritin degradation

Role in Parkinson's Disease

Genetics

PARK2 mutations are the most common cause of autosomal recessive early-onset Parkinson's disease (age of onset <40 years)[@kitada1998]. Over 200 pathogenic mutations have been identified, including:

Deletions: Whole exon deletions common
Point mutations: Missense mutations throughout the gene
Multiplications: Rare gene duplications

Common pathogenic mutations include:

C212Y: Disrupts RING1 structure
Del exons 3-5: Common in compound heterozygotes
K161N: Affects ubiquitin binding
T240R: Disrupts catalytic activity

Pathogenic Mechanisms

Loss of Mitophagy Function: Mutations impair Parkin's ability to initiate mitophagy, leading to accumulation of dysfunctional mitochondria[@scarffe2014].

Mitochondrial DNA Damage: Parkin-deficient cells show increased susceptibility to mitochondrial DNA damage.

Dysregulated Mitochondrial Dynamics: Loss of Parkin leads to excessive fission and fragmentation.

Impaired Mitochondrial Biogenesis: Reduced PGC-1α expression and decreased mitochondrial biogenesis.

Increased Apoptosis: Altered regulation of pro-apoptotic proteins.

PINK1-Parkin Pathway

The PINK1-Parkin pathway represents one of the best-characterized mechanisms in PD:

Mermaid diagram (expand to render)

Therapeutic Approaches

Gene Therapy

AAV-Parkin delivery: Gene therapy to restore functional Parkin expression[@choudhury2017]

PINK1 activation: Small molecules to activate PINK1 kinase activity

Phospho-mimetic Parkin: Engineered Parkin variants with constitutive activity

Small Molecule Activators

Parkin activators: Compounds that relieve auto-inhibition or enhance E3 activity

PINK1 stabilizers: Prevent PINK1 degradation under normal conditions

Mitophagy enhancers: Agents that promote mitochondrial clearance

Mitochondrial Protectants

CoQ10 and analogs: Support mitochondrial electron transport

Mitochondrial antioxidants: Target mitochondrial oxidative stress

Mitochondrial dynamics modulators: Promote fusion over fission

Biomarkers

Fluid Biomarkers

Plasma/serum Parkin levels: Reduced in PARK2 mutation carriers
Mitochondrial DNA: Circulating mtDNA as marker of mitochondrial dysfunction
Phospho-Ser65-ubiquitin: Potential biomarker of pathway activation

Imaging Biomarkers

PET/SPECT: Fluorodopa PET shows reduced putaminal uptake in PD
Mitochondrial imaging: Novel tracers for mitochondrial mass/function

Animal Models

Genetic Models

Parkin knockout mice: Mild phenotype, incomplete penetrance
PINK1 knockout mice: Similar to Parkin knockout
Double knockout: Synergistic effects on dopaminergic neurons
Conditional knockouts: Tissue-specific deletion models

Phenotypic Findings

Reduced striatal dopamine
Mitochondrial dysfunction in brain and peripheral tissues
Age-related motor impairment in some models
Incomplete recapitulation of human PD phenotype

Interactions and Network

Key Protein Interactions

| Partner | Interaction Type | Functional Consequence |
|---------|-----------------|----------------------|
| PINK1 | Phosphorylation | Activates Parkin |
| Phospho-ubiquitin | Binding | Activates Parkin |
| E2 enzymes | Catalysis | UbcH7, UbcH8 |
| p62/SQSTM1 | Autophagy receptor | Links to autophagosomes |
| Mfn1/2 | Substrate | Regulates fusion |
| VDAC1 | Substrate | Permeability control |
| BCL-2 | Anti-apoptotic | Regulates cell death |

Research History

1998: PARK2 locus identified as cause of autosomal recessive PD[@hattori1998]

2004: Parkin shown to have E3 ubiquitin ligase activity[@shimura2000]

2006: PINK1 phosphorylates Parkin discovered[@kim2008]

2008: PINK1-Parkin mitophagy pathway characterized[@narendra2010]

2015: Cryo-EM structures reveal auto-inhibited conformation[@riley2014]

2018: Phospho-ubiquitin as Parkin activator identified[@koyano2014]

Clinical Management

Diagnostic Considerations

Genetic testing: Important for early-onset cases
Family counseling: Autosomal recessive inheritance
Clinical trials: Consider enrollment in LRRK2 trials

The Parkin protein continues to be a major focus of PD research and therapeutic development.

References

Lücking CB, et al, (2000) (2000)

Pickrell AM, Youle RJ, (2015) (2015)

Riley BE, et al, (2014) (2014)

Narendra D, Tanaka A, Suen DF, Youle RJ, (2008) (2008)

Koyano F, et al, (2014) (2014)

Chan NC, et al, (2011) (2011)

Lazarou M, et al, (2015) (2015)

Kitada T, et al, (1998) (1998)

Scarffe LA, et al, (2014) (2014)

Choudhury SR, et al. (2017). AAV-PARKIN therapy for Parkinson's disease. Molecular Therapy. 25(1):A26, PMC5385414 (2017)

Hattori N, et al, (1998) (1998)

Shimura H, et al, (2000) (2000)

Kim Y, et al, (2008) (2008)

Narendra DP, et al, (2010) (2010)

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PARK2 Protein - Parkin

Parkin Protein — PARK2 E3 Ubiquitin Protein Ligase

Overview

Parkin Protein — PARK2 E3 Ubiquitin Protein Ligase

Overview

Structure

Key Structural Features

Normal Physiological Function

Mitochondrial Quality Control

Additional Cellular Functions

Role in Parkinson's Disease

Genetics

Pathogenic Mechanisms

PINK1-Parkin Pathway

Therapeutic Approaches

Gene Therapy

Small Molecule Activators

Mitochondrial Protectants

Biomarkers

Fluid Biomarkers

Imaging Biomarkers

Animal Models

Genetic Models

Phenotypic Findings

Interactions and Network

Key Protein Interactions

Research History

See Also

Clinical Management

Diagnostic Considerations

References