[Parkin[/proteins/[parkin[/proteins/[parkin[/proteins/[parkin[/proteins/[parkin--TEMP--/proteins)--FIX-- (Park2) is an important component in the neurobiology of neurodegenerative [diseases[/[diseases[/[diseases[/[diseases[/[diseases[/[diseases[/[diseases[/[diseases[/diseases. This page provides detailed information about its structure, function, and role in disease processes.
Parkin is an E3 ubiquitin ligase of the RING-between-RING (RBR) family, encoded by the PRKN gene (formerly PARK2). Parkin plays a central role in mitochondrial quality control through the [PINK1[/proteins/[pink1-protein[/proteins/[pink1-protein[/proteins/[pink1-protein[/proteins/[pink1-protein--TEMP--/proteins)--FIX---Parkin [mitophagy[/mechanisms/[mitophagy[/mechanisms/[mitophagy[/mechanisms/[mitophagy[/mechanisms/[mitophagy--TEMP--/mechanisms)--FIX-- pathway, which selectively targets damaged mitochondria for degradation by [autophagy[/entities/[autophagy[/entities/[autophagy[/entities/[autophagy[/entities/[autophagy--TEMP--/entities)--FIX--. Loss-of-function mutations in PRKN are the most common cause of autosomal recessive early-onset [Parkinson's disease[/diseases/[parkinsons[/diseases/[parkinsons[/diseases/[parkinsons[/diseases/[parkinsons--TEMP--/diseases)--FIX--, accounting for up to 50% of familial early-onset PD and ~15% of all early-onset cases (<45 years) (Lücking et al., 2000).
The discovery that Parkin mutations cause PD established a direct mechanistic link between [mitochondrial dysfunction[/mechanisms/[mitochondrial-dysfunction[/mechanisms/[mitochondrial-dysfunction[/mechanisms/[mitochondrial-dysfunction[/mechanisms/[mitochondrial-dysfunction--TEMP--/mechanisms)--FIX-- and parkinsonism, and the subsequent elucidation of the PINK1-Parkin pathway has become one of the most important advances in understanding selective mitophagy in both health and disease.
¶ Gene and Protein Structure
- Gene symbol: PRKN (also known as PARK2)
- Chromosomal location: 6q26
- Gene size: ~1.38 Mb (one of the largest known human [genes)
- Exons: 12 exons
- Protein: 465 amino acids (~52 kDa)
- The large gene size contributes to the high frequency of deletions and rearrangements
Parkin belongs to the RBR (RING1-IBR-RING2) family of E3 ubiquitin ligases, with a unique multi-domain autoinhibited architecture:
| Domain |
Residues |
Function |
| Ubl (ubiquitin-like) |
1-76 |
Phosphorylated by PINK1 at Ser65; activating signal; also mediates proteasomal targeting |
| Linker |
77-140 |
Connects Ubl to RING0; contains REP (repressor element of Parkin) |
| RING0 |
141-216 |
Unique to Parkin; coordinates Zn2+ ions; contributes to autoinhibition |
| RING1 |
217-314 |
Binds E2 ubiquitin-conjugating enzymes (UbcH7/UBE2L3) |
| IBR (in-between-RING) |
315-377 |
Structural domain; links RING1 to RING2 |
| REP |
378-403 |
Repressor element; blocks RING2 active site in the autoinhibited state |
| RING2 |
404-465 |
Contains the catalytic Cys431 that forms the thioester intermediate with ubiquitin |
Crystal structures revealed that Parkin is held in a deeply autoinhibited state through multiple intramolecular interactions (Trempe et al., 2013):
- The Ubl domain blocks the E2-binding site on RING1
- The REP element occludes the catalytic Cys431 in RING2
- The RING0 domain shields the Ubl phosphorylation site
- Full activation requires both Ubl phosphorylation by PINK1 and binding of phospho-ubiquitin
- Mitochondrial damage: Loss of membrane potential (ΔΨm) caused by toxins (CCCP, antimycin A), [oxidative stress[/mechanisms/[oxidative-stress[/mechanisms/[oxidative-stress[/mechanisms/[oxidative-stress[/mechanisms/[oxidative-stress--TEMP--/mechanisms)--FIX--, or mtDNA mutations
- PINK1 stabilization: Normally imported and degraded, [PINK1[/proteins/[pink1-protein[/proteins/[pink1-protein[/proteins/[pink1-protein[/proteins/[pink1-protein--TEMP--/proteins)--FIX-- accumulates on the outer mitochondrial membrane (OMM) of damaged mitochondria
- PINK1 dimerization: PINK1 forms a dimer at the TOM-VDAC complex on the OMM (2024 cryo-EM structural data)
- Ubiquitin phosphorylation: PINK1 phosphorylates ubiquitin at Ser65, generating phospho-ubiquitin (pUb) on OMM [proteins[/[proteins[/[proteins[/[proteins[/[proteins[/[proteins[/[proteins[/[proteins[/proteins
- Parkin recruitment: Cytosolic Parkin binds pUb on the OMM surface; this partially activates Parkin
- Parkin phosphorylation: PINK1 phosphorylates Parkin's Ubl domain at Ser65, fully activating the E3 ligase
- Ubiquitin chain building: Activated Parkin ubiquitinates OMM proteins (MFN1/2, VDAC1, Miro1/2, TOM20)
- Feed-forward amplification: Newly added ubiquitin chains are phosphorylated by PINK1, recruiting more Parkin — exponential amplification
- [autophagy[/entities/[autophagy[/entities/[autophagy[/entities/[autophagy[/entities/[autophagy--TEMP--/entities)--FIX-- receptor recruitment: Ubiquitin chains recruit receptors (OPTN, NDP52, TAX1BP1) that bridge the mitochondrion to LC3 on the phagophore
- Engulfment and degradation: Autophagosome engulfs the damaged mitochondrion; fusion with lysosome completes degradation
| Substrate |
Effect of Ubiquitination |
| MFN1/MFN2 (mitofusins) |
Prevents fusion with healthy mitochondria; isolates damaged organelle |
| Miro1/Miro2 |
Arrests mitochondrial motility; detaches from microtubule motors |
| VDAC1 |
Promotes autophagy receptor recruitment |
| TOM20/TOM70 |
Prevents protein import into damaged mitochondria |
| HK1/HK2 (hexokinases) |
Dissociates metabolic coupling |
Opposing Parkin-mediated ubiquitination:
- USP30: Deubiquitinase on the OMM that removes ubiquitin chains added by Parkin, opposing mitophagy. USP30 inhibitors are in clinical development as mitophagy enhancers
- USP15: Additional deubiquitinase opposing Parkin activity
- USP8: Removes K6-linked ubiquitin from Parkin itself, promoting its recycling
¶ Genetics and Parkinson's Disease
Over 200 pathogenic variants in PRKN have been identified:
| Mutation Type |
Frequency |
Examples |
| Exon deletions |
~50% |
Exon 3-4 deletion (most common); exon 2 deletion |
| Exon duplications/triplications |
~10% |
Exon 2 duplication |
| Missense mutations |
~25% |
R42P (Ubl); T240R (RING1); C431F (RING2 catalytic) |
| Truncating (nonsense/frameshift) |
~15% |
Various |
- Compound heterozygosity (two different mutations) is more common than homozygosity
- Large deletions/rearrangements are common due to the enormous gene size
- Heterozygous PRKN carriers may have increased PD risk (debated)
| Feature |
Parkin-PD |
Sporadic PD |
| Age of onset |
Typically <40 years (mean ~30) |
Typically >60 years |
| Progression |
Slow |
Variable |
| Predominant symptoms |
[Dystonia[/diseases/[dystonia[/diseases/[dystonia[/diseases/[dystonia[/diseases/[dystonia--TEMP--/diseases)--FIX-- at onset; less tremor |
Resting tremor common |
| [Levodopa[/treatments/[levodopa[/treatments/[levodopa[/treatments/[levodopa[/treatments/[levodopa--TEMP--/treatments)--FIX-- response |
Excellent (but early dyskinesias) |
Good |
| Cognitive decline |
Uncommon |
Common in later stages |
| Lewy bodies |
Usually absent (loss of α pathway) |
Present (hallmark) |
| Neuropathology |
Selective nigral [dopamine[/entities/[dopamine[/entities/[dopamine[/entities/[dopamine[/entities/[dopamine--TEMP--/entities)--FIX-- neuron loss without Lewy bodies |
Nigral loss with Lewy bodies |
The absence of Lewy bodies in most Parkin-PD cases suggests that Parkin-mediated ubiquitination may be required for [alpha-synuclein[/proteins/[alpha-synuclein[/proteins/[alpha-synuclein[/proteins/[alpha-synuclein[/proteins/[alpha-synuclein--TEMP--/proteins)--FIX-- aggregate formation.
- PRKN is located in a common fragile site (FRA6E) frequently deleted in cancer
- Parkin acts as a tumor suppressor by ubiquitinating cyclin D1 and cyclin E, promoting cell cycle arrest
- PRKN deletions found in ovarian, breast, lung, and liver cancers
- Parkin-PD patients may have altered cancer risk (epidemiological studies inconclusive)
- Parkin ubiquitinates NLRP3], suppressing inflammasome activation
- Loss of Parkin leads to heightened [neuroinflammation[/mechanisms/[neuroinflammation[/mechanisms/[neuroinflammation[/mechanisms/[neuroinflammation[/mechanisms/[neuroinflammation--TEMP--/mechanisms)--FIX-- via STING] pathway activation (mtDNA release from damaged mitochondria)
- Parkin-deficient [microglia[/cell-types/[microglia[/cell-types/[microglia[/cell-types/[microglia[/cell-types/[microglia--TEMP--/cell-types)--FIX--/cell-types/microglia entered Phase 1 [clinical trials)/clinical-trials) (2024)
- PINK1 activators: Small molecules that stabilize or activate PINK1 to compensate for reduced Parkin activity (e.g., kinetin triphosphate)
- Parkin activators: Compounds that relieve autoinhibition and promote Parkin activation
- AAV-mediated PRKN gene delivery to dopaminergic [neurons[/entities/[neurons[/entities/[neurons[/entities/[neurons[/entities/[neurons--TEMP--/entities)--FIX-- in the [substantia nigra[/brain-regions/[substantia-nigra[/brain-regions/[substantia-nigra[/brain-regions/[substantia-nigra[/brain-regions/[substantia-nigra--TEMP--/brain-regions)--FIX--
- Preclinical studies show protection against MPTP-induced neurodegeneration
- Challenge: Large gene size (~1.38 kb coding sequence) approaches AAV packaging limits
- Miro1 reduction to arrest damaged mitochondrial motility
- MFN2 modulators to prevent damaged-healthy mitochondrial fusion
- Enhancing alternative (Parkin-independent) mitophagy pathways (BNIP3L/NIX, FUNDC1)
The study of Parkin (Park2) has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying [mechanisms of neurodegeneration[/[mechanisms[/[mechanisms[/[mechanisms[/[mechanisms[/[mechanisms[/[mechanisms[/[mechanisms[/mechanisms and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
- [Microglia[/alpha-synuclein (α[-Syn[/alpha-synuclein (α[-Syn[/alpha-synuclein (α[-Syn[/alpha-synuclein (α[-Syn[/alpha-synuclein (α[-Syn[/alpha-synuclein (α[-Syn[/alpha-synuclein (α[-Syn[/alpha-synuclein (α[-Syn](/alpha-synuclein (α-Syn)(/proteins/alpha-synuclein))
- [Parkin[/proteins/[parkin[/proteins/[parkin[/proteins/[parkin[/proteins/[parkin--TEMP--/proteins)--FIX--
- [PINK1[/proteins/[pink1-protein[/proteins/[pink1-protein[/proteins/[pink1-protein[/proteins/[pink1-protein--TEMP--/proteins)--FIX--
- [Lücking CB, et al. Association between early-onset Parkinson's Disease and mutations in the parkin gene. N Engl J Med. 2000;342(21]:1560-1567. DOI
- [Trempe JF, et al. Structure of parkin reveals mechanisms for ubiquitin ligase activation. Science. 2013;340(6139:1451-1455. DOI
- [Kitada T, et al. Mutations in the parkin gene cause autosomal recessive juvenile parkinsonism. Nature. 1998;392(6676:605-608. DOI
- [Kane LA, et al. PINK1 phosphorylates ubiquitin to activate Parkin E3 ubiquitin ligase activity. J Cell Biol. 2014;205(2]:143-153. DOI
- [Koyano F, et al. Ubiquitin is phosphorylated by PINK1 to activate parkin. Nature. 2014;510(7503:162-166. DOI
- [Narendra DP, et al. Parkin is recruited selectively to impaired mitochondria and promotes their autophagy. J Cell Biol. 2008;183(5]:795-803. DOI
- [Wauer T, et al. Mechanism of phospho-ubiquitin-induced PARKIN activation. Nature. 2015;524(7565:370-374. DOI
- [Bingol B, et al. The mitochondrial deubiquitinase USP30 opposes parkin-mediated mitophagy. Nature. 2014;510(7505:370-375. DOI
- [Dawson TM, Dawson VL. Parkin plays a role in sporadic [Parkinson's disease[/diseases/[parkinsons[/diseases/[parkinsons[/diseases/[parkinsons[/diseases/[parkinsons--TEMP--/diseases)--FIX--. Neurodegener Dis. 2014;13(2-3:69-71. DOI
- [Gladkova C, et al. Mechanism of parkin activation by PINK1. Nature. 2018;559(7714:410-414. DOI