Synucleins are a family of soluble proteins common to vertebrates, primarily expressed in neural tissue and in certain tumor

Tumor

A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...

s.

Family members

The synuclein family includes three known proteins: alpha-synuclein

Alpha-synuclein

Alpha-synuclein is a protein that, in humans, is encoded by the SNCA gene. An alpha-synuclein fragment, known as the non-Abeta component of Alzheimer's disease amyloid, originally found in an amyloid-enriched fraction, is shown to be a fragment of its precursor protein, NACP, by cloning of the...

, beta-synuclein

Beta-synuclein

Beta-synuclein is a protein that in humans is encoded by the SNCB gene.Beta-synuclein is a synuclein protein found primarily in brain tissue and is seen mainly in presynaptic terminals. Beta-synuclein is predominantly expressed in the neocortex, hippocampus, striatum, thalamus, and cerebellum...

, and gamma-synuclein

Gamma-synuclein

Gamma-synuclein is a protein that in humans is encoded by the SNCG gene.Gamma-synuclein is a synuclein protein found primarily in the peripheral nervous system and retina. It is also detected in the brain, ovarian tumors, and in the olfactory epithelium...

. Interest in the synuclein family began when alpha-synuclein was found to be mutated in several families with autosomal dominant

Dominance relationship

Dominance in genetics is a relationship between two variant forms of a single gene, in which one allele masks the effect of the other in influencing some trait. In the simplest case, if a gene exists in two allelic forms , three combinations of alleles are possible: AA, AB, and BB...

 Parkinson's disease

Parkinson's disease

Parkinson's disease is a degenerative disorder of the central nervous system...

.

All synucleins have in common a highly conserved alpha-helical

Alpha helix

A common motif in the secondary structure of proteins, the alpha helix is a right-handed coiled or spiral conformation, in which every backbone N-H group donates a hydrogen bond to the backbone C=O group of the amino acid four residues earlier...

 lipid-binding motif with similarity to the class-A2 lipid-binding domains of the exchangeable apolipoproteins. Synuclein family members are not found outside vertebrate

Vertebrate

Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

s, although they have some conserved structural similarity with plant 'late-embryo-abundant' proteins.

• Alpha-synuclein
  Alpha-synuclein
  Alpha-synuclein is a protein that, in humans, is encoded by the SNCA gene. An alpha-synuclein fragment, known as the non-Abeta component of Alzheimer's disease amyloid, originally found in an amyloid-enriched fraction, is shown to be a fragment of its precursor protein, NACP, by cloning of the...
  
   
• Beta-synuclein
  Beta-synuclein
  Beta-synuclein is a protein that in humans is encoded by the SNCB gene.Beta-synuclein is a synuclein protein found primarily in brain tissue and is seen mainly in presynaptic terminals. Beta-synuclein is predominantly expressed in the neocortex, hippocampus, striatum, thalamus, and cerebellum...
  
   
• Gamma-synuclein
  Gamma-synuclein
  Gamma-synuclein is a protein that in humans is encoded by the SNCG gene.Gamma-synuclein is a synuclein protein found primarily in the peripheral nervous system and retina. It is also detected in the brain, ovarian tumors, and in the olfactory epithelium...
  
   

Function

Normal cellular functions have not been determined for any of the synuclein proteins. Some data suggest a role in the regulation of membrane stability and/or turnover. Mutations in alpha-synuclein are associated with early-onset familial Parkinson's disease and the protein aggregates abnormally in Parkinson's disease

Parkinson's disease

Parkinson's disease is a degenerative disorder of the central nervous system...

, Alzheimer's disease

Alzheimer's disease

Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...

, Lewy body disease

Lewy body

Lewy bodies are abnormal aggregates of protein that develop inside nerve cells in Parkinson's disease , Lewy Body Dementia and some other disorders. They are identified under the microscope when histology is performed on the brain....

, and other neurodegenerative diseases. The gamma-synuclein protein's expression in breast tumors

Breast cancer

Breast cancer is cancer originating from breast tissue, most commonly from the inner lining of milk ducts or the lobules that supply the ducts with milk. Cancers originating from ducts are known as ductal carcinomas; those originating from lobules are known as lobular carcinomas...

is a marker for tumor progression.