title: Solution structure of an amyloid-forming protein during photoinitiated hexamer-dodecamer transitions revealed through small-angle neutron scattering.
abstract: Shape-reconstruction analysis applied to small angle neutron scattering (SANS) data is used to determine the in vitro conformations of alpha-chymotrypsin oligomers that form as a result of partial unfolding with a photoresponsive surfactant. In the presence of the photoactive surfactant under visible light, the native oligomers (dimers or compact hexamers) rearrange into expanded corkscrew-like hexamers. Converting the surfactant to the photopassive 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 photoinduced hexamer-to-dodecamer association occurs through intermolecular beta 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 direct observation of the mechanism of oligomeric formation in an amyloid-forming protein. Combined with photoinitiated 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.
authors.affiliation: Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-1211, USA.
authors.forename: Andrea C
authors.initials: AC
authors.lastname: Hamill
authors.forename: Shao-Chun
authors.initials: SC
authors.lastname: Wang
authors.forename: C Ted
authors.initials: CT
authors.lastname: Lee
mesh_terms: D000682:Amyloid / Q000737:chemistry*; D000818:Animals; D002417:Cattle; D002918:Chymotrypsin / Q000737:chemistry* / Q000528:radiation effects; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D033363:Neutron Diffraction; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D053838:Scattering, Small Angle; D017550:Spectroscopy, Fourier Transform Infrared; D014466:Ultraviolet Rays; D014961:X-Ray Diffraction
chemical_list: D000682:Amyloid; D000644:Quaternary Ammonium Compounds; C006664:4-azobenzenetrimethylammonium; D002918:Chymotrypsin; C117608:alpha-chymotrypsin