(205g) Structure Of Pre-Amyloid Oligomers During Photoreversible Hexamer-Dodecamer Transitions From Small-Angle Neutron Scattering

Shape-reconstruction analysis applied to small angle neutron scattering (SANS) data is used to determine the in vitro conformations of α-chymotrypsin oligomers that form as a result of partial unfolding with a photoresponsive surfactant. In the presence of the photo-active surfactant under visible light, the native oligomers (dimers or compact hexamers) rearrange into expanded corkscrew-like hexamers. Converting the surfactant to the photo-passive form with UV-light illumination causes the hexamers to laterally aggregate and intertwine into dodecamers with elongated, twisted conformations containing cross-sectional dimensions similar to amyloid protofilaments. Secondary-structure measurements with FT-IR indicate that this photo-induced hexamer-to-dodecamer association occurs through intermolecular β sheets stabilized with hydrogen bonds, similar to amyloid formation. Traditional structural characterization techniques such as X-ray crystallography and NMR are not easily amenable to the study of these non-native protein conformations; however, SANS is ideally suited to the study of these associated intermediates, providing the first direct observation of the mechanism of oligomeric formation in an amyloid-forming protein. Combined with photo-initiated hexamer-to-dodecamer associations in the presence of the photoresponsive surfactant, this study could provide unique insight into the amyloidosis disease pathway, as well as novel disease treatment strategies.