Dissecting structure of prion amyloid fibrils by hydrogen-deuterium exchange ultraviolet Raman spectroscopy

The molecular mechanisms underlying structural diversity of amyloid fibrils or prion strains formed within the same primary structure is considered to be one of the most enigmatic questions in prion biology. We report here on the direct characterization of amyloid structures using a novel spectroscopic technique, hydrogen-deuterium exchange ultraviolet Raman spectroscopy. This method enables us to assess the structural differences within highly ordered cross-β-cores of two amyloid states produced within the same amino acid sequence of full-length mammalian prion protein. We found that while both amyloid states consisted of β-structures, their cross-β-cores exhibited hydrogen bonding of different strengths. Moreover, Raman spectroscopy revealed that both amyloid states displayed equally narrow crystalline-like bands, suggesting uniform structures of cross-β-cores within each state. Taken together, these data suggest that highly polymorphous fibrils can display highly uniform structures of their cross-β-core and belong to the same prion strain.