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Abstract

The aggregation of alpha-synuclein is characteristic of Parkinson’s disease (PD) and other neurodegenerative synucleinopathies. The 140-aa protein is natively unstructured; thus, ligands binding to the monomeric form are of therapeutic interest. Biogenic polyamines promote the aggregation of alpha-synuclein and may constitute endogenous agents modulating the pathogenesis of PD. We characterized the complexes of natural and synthetic polyamines with alpha-synuclein by NMR and assigned the binding site to C-terminal residues 109–140. Dissociation constants were derived from chemical shift perturbations. Greater polyamine charge (+2-+5) correlated with increased affinity and enhancement of fibrillation, for which we propose a simple kinetic mechanism involving a dimeric nucleation center. According to the analysis, polyamines increase the extent of nucleation by B104 and the rate of monomer addition B40-fold. Significant secondary structure is not induced in monomeric alpha-synuclein by polyamines at 151C. Instead, NMR reveals changes in a region (aa 22–93) far removed from the polyamine binding site and presumed to adopt the beta-sheet conformation characteristic of fibrillar alpha-synuclein. We conclude that the C-terminal domain acts as a regulator of alpha-synuclein aggregation.