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Variant-specific dynamics of amyloid-b fibrils

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One of the hallmarks of Alzheimer?s disease (AD) is the presence of neurotoxic amyloid-? (A?) deposits in brain tissue. All A? species from oligomers to fibrils exist in a dynamic equilibrium, which is believed to trigger a pathological cascade implicating other aggregation-prone proteins. The so-called polymorphism of A? exists at multiple levels, from the length and molecular modifications of A? to the morphological differences within the same molecular structure, to general conformational diversities and dynamics within a single structural unit. The post-translational modifications (PTMs) have been recently implicated in sporadic AD onset, as they are thought to trigger or accelerate the fibrillation of the wild-type A? peptide and enhance its toxicity. Further, membrane-A? interactions and the resulting aggressive oligomeric/protofibrils mixtures are increasingly implicated in elevated cytotoxicities. The long-term goal of our research is the correlation of the intrinsic flexibility of A? species with existing structural, aggregation, and toxicitiy studies in order to pinpoint the role of conformational ensembles in promoting more toxic/aggressive states. Having established the main features of the intrinsic flexibility of the wild-type A? fibrils, as well as the key flexibility features of the disordered N-terminal domain of several PTMs in our previous studies, we propose to examine which features of conformational ensembles propagate into the cross-seeded species and what other dynamical alterations are seen compared with the self-seeded wild- type A?. The goal of the proposed work is to obtain quantitative site-specific characterizations of dynamics in the A?1-40 fibrils originating from the seeded growth of several strategically chosen systems: a) seeds with PTMs of A?1-40 in the N-terminal region, which have been found to enhance fibrillation kinetics and toxicities; and b) seeds produced in the presence of high concentration of synaptic plasma membrane vesicles from rats? brain tissues (SV). The latter can be at least partially treated within the same paradigm as PTMs, assuming that the interactions between the SV surface and A? oligomer/protofibrils/fibrils mixtures create unique conformational ensembles that can be considered to be a ?modification? analogous in its seeding actions to PTMs with relatively aggressive aggregation propensities. We hypothesize that a range of dynamical features propagate from the PTMs or SV seeds to the wild-type A? fibrils and that these ?conserved? features may be the most important for the correlations with aggregation propensities and cross-seeding aggressiveness. The joint investigation of the SV-A? interactions and PTM cross-seeding imprint can advance our understanding of the relationship between the amyloid fibril polymorphism and aggregation aggressiveness, ultimately shedding light on potentially relevant pathological features. Our main tools are static deuterium solid-state NMR and computational modeling for the assessment of the dynamics, and transmission electron microscopy for characterization of the morphologies. The PI is extremely committed to training undergraduate students from diverse background and proposes to train several students in sample preparation, spectroscopy, and modeling aspects.
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