Elucidating the mechanism of amyloid-beta's pathological aggregation

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7. Project summary/Abstract Alzheimer's disease (AD), the most common neurodegenerative disorder, is an age-dependent disorder resulting in progressive loss of cognitive function. It affects more than 4 million people in the United States and is therefore a highly relevant factor in the elderly's quality of life. The symptoms of the disease strongly correlate with the presence of transiently formed and soluble aggregates of amyloid-β (Aβ) in the brains of AD patients. Because of the relevance Alzheimer's to public health, there is substantial interest in understanding the molecular mechanism of AD and treating the disease. Nevertheless, the short-lived nature of the Aβ soluble intermediates formed during the course of its pathological aggregation presents a formidable challenge to the traditional techniques used for the investigation of biological molecules. Although progress has been made in studying these molecules, by making slight chemical modifications that increase their stability, for example, it is not known whether the molecular behavior observed in these studies is completely relevant to the behavior of Aβ in humans. In the Frydman lab techniques have been developed that allow the fast characterization of features of biological molecules relevant to their behavior (structure and dynamics). We propose to use these techniques, a suite of ultrafast NMR experiments, to investigate the structure and dynamics of Aβ as it undergoes aggregation. Ultrafast TOCSY and STD-TOCSY experiments will be used to probe the interaction between Aβ monomers and oligomers during the aggregation process. The diffusive dynamics of the system will be probed by ultrafast DOSY experiments, which separates resonances according to the hydrodynamic radii associated with the chemical sites to which they belong. Further functional insights will also be gained from site-resolved longitudinal relaxation measurements, which reveal the mobility of molecular fragments-and hence their degree of polymerization. This proposal aims to uncover detailed structural information about Aβ's folded monomeric state, which is believed to play a crucial role in the formation of a nucleus for Aβ's aggregation. In aqueous solution, folded conformers of Aβ undergo conformational exchange with its random coil state. Using the innovative selective dynamic recoupling (SDR) technique that I have developed, the chemical shifts of folded Aβ conformers will be revealed, which can be used to probe their structures. The in vivo behavior of Aβ in a cellular environment is believed to play a significant role in its pathology. I plan to uncover detailed information on the intracellular behavior of Aβ by performing NMR experiments in living Xenopus laevis oocytes.