Alpha-synuclein is a natively unfolded protein composed of 140 amino acids predominantly localized in the presynaptic terminals of neurons. It is expressed in several parts of the brain, presenting high levels in the neocortex, hippocampus, substantia nigra, thalamus, and cerebellum.

The exact function of alpha-synuclein remains unknown, although it is thought that it plays a role in maintaining a supply of synaptic vesicles inside the neurons. Thus, alpha-synuclein may regulate the release of neurotransmitters such as dopamine that leads to controlling voluntary and involuntary movements. In addition, several studies conducted in mice show that it might also influence memory and cognitive function. Therefore, these roles could make alpha-synuclein a major contributory factor in neurodegeneration.