Progress in FY2009 has been in the following areas: 1. INITIAL STUDIES OF AMYLOID FIBRIL STRUCTURES DERIVED FROM BRAIN TISSUE: We have completed and published our initial studies of beta-amyloid fibrils prepared from synthetic peptide by seeding with amyloid fibrils extracted from brain tissue of deceased Alzheimer's disease patients (collaboration with S.C. Meredith, University of Chicago). Our data indicate that brain-seeded fibrils have a single predominant morphology and molecular structure, and that the structure differs from structures we have examined in previous work on purely synthetic samples. This seeding approach gives us a method for characterizing the molecular structures of in vivo fibrils by solid state NMR and electron microscopy. Future work will seek to identify structural variations among in vivo fibrils that may correlate with neurodegeneration or with localization within the brain. We are currently refining our protocol for extracting amyloid from brain tissue and using this material to seed fibril growth, with the goals of reducing the required amount of tissue and ensuring that seeded fibrils are truly representative of fibril structures in the brain. This will allow us to extend our research to many more tissue samples. 2. SURPRISING ANTIPARALLEL BETA-SHEET STRUCTURE IN MUTANT BETA-AMYLOID FIBRILS: Again in collaboration with S.C. Meredith, we have shown that the Asp23-to-Asn mutant of human beta-amyloid (D23N mutant, or Iowa mutant) is capable of forming amyloid fibrils that contain antiparallel beta-sheets. This is the first demonstration that a full-length peptide or protein could form fibrils that contain antiparallel (rather than parallel) beta-sheets. This work has been published in Biochemistry. In the original experiments, D23N fibril samples were heterogeneous, comprising a mixture of parallel and antiparallel beta-sheet structures. We have now developed fibril formation conditions that produce homogeneous antiparallel structures, and have begun determining their detailed molecular structure. In future work, we will test whether the wild-type beta-amyloid peptide can be induced to form antiparallel structures, by seeding with the mutant peptide fibrils. The D23N mutant is found in an Iowa family with a history of early-onset, congenital neurodegenerative disease, principally cerebral amyloid angiopathy. Our work raises the possibility that this unusual molecular structural variant is responsible for the disease.
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