Monomeric a-synuclein (aS) inhibits amyloidogenesis of human prion protein (hPrP) by forming a stable aS-hPrP hetero-dimer.

Intermolecular interaction between hPrP and αS was investigated using high-speed atomic force microscopy, dynamic light scattering, and nuclear magnetic resonance. We found that hPrP spontaneously gathered and naturally formed oligomers. Upon addition of monomer αS with a disordered conformation, poly-dispersive property of hPrP was lost, and hetero-dimer formation started quite coherently, and further oligomerization was not observed. Solution structure of hPrP-αS dimer was firstly characterized using hetero-nuclear NMR spectroscopy. In this hetero-dimeric complex, C-terminal helical region of hPrP was in the molten-globule like state, while specific sites including hot spot and C-terminal region of αS selectively interacted with hPrP. Thus αS may suppress amyloidogenesis of hPrP by trapping the hPrP intermediate by the formation of a stable hetero-dimer with hPrP.Abbreviations: hPrP, human prion protein of amino acid residues of 23-231; PrP^C, cellular form of prion protein; PrP^Sc, scrapie form of prion protein, HS-AFM; high speed atomic force microscopy; αS, α-synuclein; DLS, dynamic light scattering.