Alpha-synuclein dysfunction in Lewy body diseases.

alpha-Synuclein belongs to a small group of natively unfolded proteins that can transiently bind to lipid membranes and acquire a partial alpha-helical conformation. Its relevance to Parkinson's disease (PD) is based on mutations found in familial cases of the disease and its presence in filaments of Lewy bodies (LB) and Lewy neurites (LN) in sporadic cases where it is packed in a beta-sheet configuration. This structural plasticity of alpha-synuclein has raised the possibility that neurodegeneration may be a consequence of abnormal protein folding. The extent to which abnormal folding and aggregation of neuronal proteins is directly toxic to the cell, an inert biochemical marker of an underlying harmful metabolic defect, or a protective reaction remains to be seen. We review the function of alpha-synuclein and recent studies that have shed light on the mechanisms by which it aggregates.