α-synuclein

α-synuclein

α-synuclein is a protein abundant in the human brain that, under pathological conditions, can misfold and aggregate into toxic clumps known as Lewy bodies, a hallmark of Parkinson's disease and other related neurodegenerative disorders.

In its healthy state, α-synuclein is a small, soluble protein found primarily at the presynaptic terminals of neurons—the tips of nerve cells that release chemical messengers called neurotransmitters. While its precise function is still under investigation, it is believed to play a crucial role in regulating the release of these neurotransmitters, particularly dopamine, by interacting with synaptic vesicles that store them. Normally, the protein is natively unfolded, but it can adopt a helical structure upon binding to lipid membranes, suggesting a dynamic role in synaptic function and plasticity.

The pathology of several neurodegenerative diseases begins when α-synuclein misfolds and starts to clump together. This process is thought to occur in a stepwise fashion, where individual protein units (monomers) aggregate into small, toxic clusters (oligomers) and then into larger, insoluble fibrils. These fibrils are the primary component of the microscopic inclusions found within neurons called Lewy bodies and Lewy neurites. The accumulation of these aggregates is cytotoxic, meaning it is harmful to cells. They are believed to disrupt essential cellular processes, including mitochondrial function (the cell's energy production), the ubiquitin-proteasome system (the cell's waste disposal machinery), and the normal flow of information at the synapse, ultimately leading to neuronal dysfunction and death.

Context in Neurodegeneration

α-synuclein is the defining pathological protein for a group of disorders known as synucleinopathies. This category includes Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). The specific clinical symptoms of each disease are largely determined by which brain regions are most affected by α-synuclein aggregation. This concept of protein misfolding is a central theme in neurodegenerative science, placing α-synuclein alongside other key proteins like amyloid-beta and tau in Alzheimer's disease. Furthermore, emerging evidence supports a "prion-like" hypothesis, which posits that misfolded α-synuclein can spread from an affected neuron to a healthy one, thereby propagating the pathology throughout the nervous system over time.