Synuclein proteins exist as three distinct forms, α-, β-, and γ-synuclein. The α-synuclein protein is primarily found in neural tissue, making up as much as 1% of all proteins in the cytosol of brain cells, and is 140 amino acids long in humans and rodents. β-Synuclein proteins are 134 amino acids long, and are the most conserved of the synuclein proteins, and human γ-synuclein is 127 amino acids long. α- and β- Synucleins are more closely related to each other than to γ-synuclein. All three human synuclein genes are highly expressed in the brain, with α- and γ-synuclein more widely expressed than β-synuclein. α-and β-Synuclein are found predominantly in nerve terminals in close proximity to synaptic vesicles.
α-Synuclein molecules form the major component of Lewy bodies and Lewy neurites, the abnormal aggregations of protein that develop inside nerve cells and characterise Parkinson’s disease (PD). α-Synuclein is also a constituent of the amyloid plaques of AD patients. Disorders where α-synuclein aggregates form insoluble fibrils characterized by Lewy bodies are known as synucleinopathies. β- and γ-Synucleins have not been detected in Lewy bodies or Lewy neurites although γ-synuclein is overexpressed in breast and ovarian cancer.