# Synuclein
**Synucleins** are a family of three small, intrinsically disordered neuronal proteins, α-synuclein, β-synuclein, and γ-synuclein, encoded in humans by the *SNCA*, *SNCB*, and *SNCG* genes and best known because α-synuclein aggregates are the defining pathology of [Parkinson's disease](https://www.edgepedia.org/parkinsons-disease) and related synucleinopathies.[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9303453/) • [2](https://www.mdpi.com/2227-9059/10/12/3241) The proteins are abundant at presynaptic nerve terminals, and their normal physiological functions, while increasingly well mapped, remain less fully characterized than their disease roles.[3](https://www.annualreviews.org/content/journals/10.1146/annurev-neuro-112723-051616)
| Key fact | Detail |
|---|---|
| Family members | α-synuclein (140 amino acids), β-synuclein (134), γ-synuclein (127); genes *SNCA*, *SNCB*, *SNCG*[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9303453/) |
| Structure | Small, natively unfolded (intrinsically disordered) proteins; calculated mass near 14,000 Da but apparent mass of about 19–20 kDa, indicating post-transcriptional modification[2](https://www.mdpi.com/2227-9059/10/12/3241) • [4](https://genome.cshlp.org/content/8/9/871) |
| Location | α- and β-synuclein concentrated in presynaptic nerve terminals; γ-synuclein present throughout nerve cells[5](https://www.nature.com/articles/35081564) |
| Disease link | α-synuclein is the major component of Lewy bodies and Lewy neurites, the hallmark deposits of Parkinson's disease; *SNCA* mutations cause autosomal dominant early-onset Parkinson's (A30P, A53T)[6](https://doi.org/10.1016/j.bbadis.2011.10.002) • [7](https://faseb.onlinelibrary.wiley.com/doi/full/10.1096/fj.03-0338rev) |
| Synucleinopathies | Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy are characterized by pathological α-synuclein aggregation in neuronal and glial cells[8](https://pubmed.ncbi.nlm.nih.gov/40508212/) |
| Cancer link | γ-synuclein is overexpressed in breast carcinomas and may also be overexpressed in ovarian cancer[4](https://genome.cshlp.org/content/8/9/871) |
| Abundance | α-synuclein represents about 1% of all cytosolic proteins in neurons[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9303453/) |
## History and naming
The first synuclein was isolated in 1988 from the electric ray *Torpedo californica* using an antiserum against cholinergic vesicles. Because the protein localized to the nuclear envelope of neurons and to presynaptic nerve terminals, it was named synuclein, combining "synapse" and "nucleus".[4](https://genome.cshlp.org/content/8/9/871) A second thread came from Alzheimer's disease research: a peptide solubilized from amyloid plaques was termed NAC, for non-Aβ component of AD amyloid, and its precursor protein NACP was found to be homologous to rat α-synuclein.[4](https://genome.cshlp.org/content/8/9/871) A 14-kDa phosphoneuroprotein identified in rat and bovine brain was then recognized as a family member, and NACP and the human ortholog of that protein were named α-synuclein and β-synuclein respectively by Jakes and colleagues in 1994. γ-synuclein was isolated and characterized as a new human family member in 1997.[4](https://genome.cshlp.org/content/8/9/871) Older names still in the literature reflect this history: α-synuclein is also known as the NAC precursor protein or synelfin, β-synuclein as phosphoneuroprotein 14 (PNP14), and γ-synuclein as breast cancer-specific gene 1 (BCSG1) or persyn.[9](https://pmc.ncbi.nlm.nih.gov/articles/PMC5399969/)
Phylogenetic analysis shows α- and β-synucleins are more closely related to each other than either is to γ-synuclein; the original *Torpedo* protein is actually more closely related to γ-synuclein.[4](https://genome.cshlp.org/content/8/9/871) Well-conserved homologues exist in birds, mice, cattle, and rats, but no homologues have been reported in lower organisms such as *E. coli*, yeast, *C. elegans*, or *Drosophila*.[7](https://faseb.onlinelibrary.wiley.com/doi/full/10.1096/fj.03-0338rev)
## Structure and normal function
Synucleins are natively unfolded proteins: in solution they lack a fixed three-dimensional structure, although α-synuclein can adopt different conformational states depending on conditions and cofactors, most notably folding into amphipathic helices when bound to lipid membranes.[2](https://www.mdpi.com/2227-9059/10/12/3241) • [6](https://doi.org/10.1016/j.bbadis.2011.10.002) [Alpha-synuclein](https://www.edgepedia.org/alpha-synuclein) comprises three functionally distinct regions that mediate membrane binding, vesicle clustering, and protein-protein interactions.[3](https://www.annualreviews.org/content/journals/10.1146/annurev-neuro-112723-051616)
**Presynaptic roles.** Within synapses, α-synuclein is involved in several stages of neurotransmitter signaling, such as structuring the reserve pool of vesicles, assembling the machinery for release, and recovering synaptic vesicles.[3](https://www.annualreviews.org/content/journals/10.1146/annurev-neuro-112723-051616) It promotes SNARE-complex assembly in vivo and in vitro, and interacts with molecular partners including lipid membranes, [SNARE proteins](https://www.edgepedia.org/snare-proteins), cytoskeletal components, and vesicular trafficking machinery.[8](https://pubmed.ncbi.nlm.nih.gov/40508212/) Recent data suggest a normal role for endogenous synucleins in dilation of the exocytic fusion pore, while overexpression slows synaptic vesicle exocytosis.[10](https://www.annualreviews.org/content/journals/10.1146/annurev-pathol-031920-092547) The protein is produced in large amounts during central nervous system development, when it promotes synaptogenesis and maturation of neuronal precursors.[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9303453/)
**Distribution.** α- and β-synuclein colocalize physiologically in presynaptic terminals, but with aging α-synuclein may redistribute to the neuronal soma with a relative decrease in synaptic levels.[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9303453/) γ-synuclein is expressed mainly in retinal and peripheral neurons and in adipose tissue, and it regulates kinase activity and cell cycle checkpoints.[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9303453/) • [11](https://pmc.ncbi.nlm.nih.gov/articles/PMC8773819/) β-synuclein accounts for 75–80% of the total synuclein mRNA pool in the human body, whereas α-synuclein is the most abundant synuclein protein.[11](https://pmc.ncbi.nlm.nih.gov/articles/PMC8773819/)
The three proteins show partial functional redundancy. Knockout studies in mice reveal that although the synucleins can at least partially compensate for one another, some functions are specific to a particular member, so the remaining synucleins cannot fully compensate for a lost family member.[9](https://pmc.ncbi.nlm.nih.gov/articles/PMC5399969/) • [11](https://pmc.ncbi.nlm.nih.gov/articles/PMC8773819/) All three family members affect synapse function, but their specific roles differ; β- and γ-synucleins modulate the synaptic vesicle binding of α-synuclein.[12](https://www.cell.com/article/S2211124722004272/pdf)
## Synucleinopathies
Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy are collectively called synucleinopathies because each is characterized by pathological aggregation of α-synuclein in neuronal and glial cells, leading to cellular dysfunction and neurodegeneration.[8](https://pubmed.ncbi.nlm.nih.gov/40508212/) α-synuclein was identified as the main component of Lewy bodies and Lewy neurites, the defining neuropathological features of Parkinson's disease, and α-synuclein-containing Lewy bodies are also found in dementia with Lewy bodies, whereas multiple system atrophy is characterized primarily by α-synuclein-rich glial cytoplasmic inclusions.[5](https://www.nature.com/articles/35081564) • [21](https://www.annualreviews.org/content/journals/10.1146/annurev-pathmechdis-051122-104528) Only α-synuclein is found in Lewy bodies; no genetic links between β- or γ-synuclein and neurodegenerative disease have been established, and both are considered far less pathogenic.[13](https://etheses.whiterose.ac.uk/id/eprint/30337/1/Dickens_SMD_FBS_PhD_2022.pdf) • [14](https://pmc.ncbi.nlm.nih.gov/articles/PMC2094134/)
**Aggregation and spread.** Aggregates range from oligomers to fibrils, display strain-like properties, and propagate in a prion-like manner between cells; transmission via the vagus nerve has been proposed as a route for gut-derived α-synuclein pathology to reach the central nervous system.[8](https://pubmed.ncbi.nlm.nih.gov/40508212/) Dysregulation of protein clearance pathways, including chaperone-mediated autophagy and the ubiquitin-proteasome system, exacerbates accumulation, and post-translational modifications influence toxicity and aggregation propensity.[8](https://pubmed.ncbi.nlm.nih.gov/40508212/) Genetic mutations, aging, and environmental factors accelerate misfolding and aggregation.[15](https://www.sciencedirect.com/science/article/pii/S0306452226001284) There is still no consensus on which toxic form of the protein, oligomer or fibril, drives neurodegeneration, which has hampered use of the protein as a therapeutic target.[16](https://pubmed.ncbi.nlm.nih.gov/26190401/)
**Pathological modifications.** The predominant pathological α-synuclein modification is phosphorylation at serine residue 129; this modification is specific to Lewy bodies, and antibodies against phosphorylated α-synuclein are used by pathologists in post-mortem diagnosis of synucleinopathies.[13](https://etheses.whiterose.ac.uk/id/eprint/30337/1/Dickens_SMD_FBS_PhD_2022.pdf)
**Genetics.** Missense mutations in the α-helix-forming domain of *SNCA*, A53T (alanine to threonine at position 53) and A30P (alanine to proline at position 30), cause autosomal dominant heritable early-onset Parkinson's disease.[7](https://faseb.onlinelibrary.wiley.com/doi/full/10.1096/fj.03-0338rev) Lipidic environments that promote α-synuclein folding also accelerate its aggregation, suggesting the lipid-associated conformation may be relevant to misfolding in disease.[7](https://faseb.onlinelibrary.wiley.com/doi/full/10.1096/fj.03-0338rev)
## β- and γ-synuclein in disease
β-synuclein aggregates less readily than α-synuclein in vitro and has been reported to protect against α-synuclein aggregation in vitro and against α-synuclein-mediated toxicity in vivo.[14](https://pmc.ncbi.nlm.nih.gov/articles/PMC2094134/) In contrast to α-synuclein, β-synuclein is absent from Lewy bodies.[17](https://www.frontiersin.org/journals/aging-neuroscience/articles/10.3389/fnagi.2022.818606/full) γ-synuclein entered the disease literature through cancer: the breast cancer-specific gene 1 (BCSG1) transcript was greatly over-represented in cDNA libraries from human breast cancers versus normal breast tissue, and increased γ-synuclein expression correlates with breast cancer progression.[18](https://www.sciencedirect.com/science/article/pii/S0166223697012137) • [4](https://genome.cshlp.org/content/8/9/871)
## Biomarkers
α-synuclein has been investigated extensively in cerebrospinal fluid (CSF) and blood as a potential biomarker for synucleinopathies, and β-synuclein CSF and blood levels appear to reflect synaptic damage and neurodegeneration independent of the presence of synucleinopathy.[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC9303453/) CSF α-synuclein species, including total, oligomeric, pS129, and truncated forms, are promising candidate biomarkers for Parkinson's disease.[17](https://www.frontiersin.org/journals/aging-neuroscience/articles/10.3389/fnagi.2022.818606/full) A systematic review of in vivo detection methods concluded that immunofluorescence on biopsied skin tissue and the seed amplification assay on CSF, which detects the seeded growth of misfolded α-synuclein, show the best diagnostic accuracy and reliability among the studies performed to date.[19](https://link.springer.com/article/10.1186/s13024-025-00914-0) A positive seed amplification assay confirms the presence of aggregated α-synuclein but does not by itself identify the underlying disease, and its diagnostic performance varies across study cohorts.[20](https://www.mdpi.com/2039-7283/15/6/107/pdf?version=1748940304)
## References
1. [Alpha and Beta Synucleins: From Pathophysiology to Clinical Application as Biomarkers, Movement Disorders (2022)](https://pmc.ncbi.nlm.nih.gov/articles/PMC9303453/)
2. [Synucleins: New Data on Misfolding, Aggregation and Role in Diseases, Biomolecules (2022)](https://www.mdpi.com/2227-9059/10/12/3241)
3. [Sheehan, G. D. and Ding, J. B. (2026). Synucleins in Neural Physiology: Understanding Endogenous Function to Better Contextualize Pathology. Annual Review of Neuroscience 49:273–288](https://www.annualreviews.org/content/journals/10.1146/annurev-neuro-112723-051616)
4. [The Synuclein Family, Genome Research (1998)](https://genome.cshlp.org/content/8/9/871)
5. [Goedert, M. (2001). Alpha-synuclein and neurodegenerative diseases. Nature Reviews Neuroscience 2:492–501](https://www.nature.com/articles/35081564)
6. [α-Synuclein misfolding and Parkinson's disease, Biochimica et Biophysica Acta (2012)](https://doi.org/10.1016/j.bbadis.2011.10.002)
7. [α-Synuclein and Parkinson's disease, The FASEB Journal (2004)](https://faseb.onlinelibrary.wiley.com/doi/full/10.1096/fj.03-0338rev)
8. [α-Synuclein Pathology in Synucleinopathies: Mechanisms, Biomarkers, and Therapeutic Challenges (2025)](https://pubmed.ncbi.nlm.nih.gov/40508212/)
9. [Looking at the recent advances in understanding α-synuclein and its aggregation through the proteoform prism (2017)](https://pmc.ncbi.nlm.nih.gov/articles/PMC5399969/)
10. [The Membrane Interactions of Synuclein: Physiology and Pathology, Annual Review of Pathology (2020)](https://www.annualreviews.org/content/journals/10.1146/annurev-pathol-031920-092547)
11. [β-Synuclein: An Enigmatic Protein with Diverse Functionality (2022)](https://pmc.ncbi.nlm.nih.gov/articles/PMC8773819/)
12. [Synaptic vesicle binding of α-synuclein is modulated by β- and γ-synucleins, Cell Reports (2022)](https://www.cell.com/article/S2211124722004272/pdf)
13. [Dickens, S. (2022). PhD thesis, University of Sheffield, on α-synuclein in Lewy bodies](https://etheses.whiterose.ac.uk/id/eprint/30337/1/Dickens_SMD_FBS_PhD_2022.pdf)
14. [Residual structure, backbone dynamics, and interactions within the synuclein family (2007)](https://pmc.ncbi.nlm.nih.gov/articles/PMC2094134/)
15. [Multifaceted performances of α-synuclein in health and neurological diseases, Neuroscience (2026)](https://www.sciencedirect.com/science/article/pii/S0306452226001284)
16. [Structure, function and toxicity of alpha-synuclein: the Bermuda triangle in synucleinopathies, Journal of Neurochemistry (2015)](https://pubmed.ncbi.nlm.nih.gov/26190401/)
17. [Proteomics Challenges for the Assessment of Synuclein Proteoforms as Clinical Biomarkers in Parkinson's Disease, Frontiers in Aging Neuroscience (2022)](https://www.frontiersin.org/journals/aging-neuroscience/articles/10.3389/fnagi.2022.818606/full)
18. [The synucleins: a family of proteins involved in synaptic function, plasticity, neurodegeneration and disease, Trends in Neurosciences (1998)](https://www.sciencedirect.com/science/article/pii/S0166223697012137)
19. [Diagnostic biomarkers for α-synucleinopathies: state of the art and future developments, a systematic review, Molecular Neurodegeneration (2025)](https://link.springer.com/article/10.1186/s13024-025-00914-0)
20. [Alpha-Synuclein Seed Amplification Assays in Parkinson's Disease: A Systematic Review and Network Meta-Analysis, Clinical Practice (2025)](https://www.mdpi.com/2039-7283/15/6/107/pdf?version=1748940304)
21. [annualreviews.org](https://www.annualreviews.org/content/journals/10.1146/annurev-pathmechdis-051122-104528)
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*Topic: Encyclopedia › Life and health › Biological foundations › Biochemistry and metabolism › Protein families and complexes › Neural and sensory tissue proteins*
*Initially written Oct 21, 2026*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license