Structural Studies of Alzheimer's beta-Amyloid Fibrils

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Progress in FY2015 has been in the following areas: (1) AMYLOID FIBRIL STRUCTURES DERIVED FROM BRAIN TISSUE: In collaboration with Prof. John Collinge of University College London, we have obtained solid state NMR and electron microscopy data for fibrils derived from 36 brain tissue samples from autopsies of AD patients in four categories (typical long history, posterior cortical atrophy, short duration, nondemented). Using our published amyloid extraction and seeding protocols, isotopically labeled fibrils were prepared using both 40-residue and 42-residue beta-amyloid peptides. The solid state NMR data suggest that most AD patients develop the same predominant 40-residue fibril structure in their brains, but that short duration patients can develop different and more heterogeneous structures. Results for 42-residue fibrils indicate no clear correlation between patient category and molecular structure. We have explored various approaches to data analysis, and are now in the process of writing a manuscript to report these results. (2) SOLID STATE NMR STUDIES OF THE BETA-AMYLOID ASSEMBLY PROCESS: We have used solid state NMR to examine the progression of conformational changes and changes in supramolecular organization as the beta-amyloid peptide goes from a monomeric state to an oligomeric state to a protofibrillar state and finally to a true amyloid fibril state. These experiments are enabled by the low-temperature dynamic nuclear polarization apparatus developed in our lab. We find that the principal conformational features (two separate beta-strand segments) are present even at the earliest stages of self-assembly, but that the degree of conformational order increases monotonically. Moreover, the in-register parallel beta-sheet structure does not appear until the final amyloid fibril state. This work has been published in J. Am. Chem. Soc.