PROJECT SUMMARY/ABSTRACT Alzheimer's disease (AD) is the 6th leading cause of death in US, with prevalence expected to triple by 2050. The lack of effective therapies prompts research into the molecular basis of pathology. AD and many other neurodegenerative diseases are characterized by pathological fibril aggregates of the protein tau in the brain, which spread in a prion-like manner and may be the cause of neurodegeneration. Recently, a 3.5 Å structure of the rigid core of tau fibrils from human patients with AD was solved through cryo-electron microscopy (cryo-EM). This structure allowed a glimpse of the molecular basis of tau pathology in AD, but left open questions about the remainder of the protein: only 73 residues were well ordered, and there was no information about the incorporation of 3R and 4R tau isoforms. The current proposal seeks to investigate the structure and dynamics of AD tau fibrils using solid-state NMR. I propose to amplify AD patient brain-derived tau fibrils using 13C, 15N-labelled monomers. This will result in isotopically labelled fibrils with the same structure as the AD brain fibrils, which will then be studied using solid-state NMR. Our group has recently demonstrated the first structural and dynamical investigation of a full-length in vitro tau fibril using SSNMR. If successful, this work will develop improved techniques for seeded amplification of AD brain tau fibrils, which will pave the way for extensive biochemical and structural characterization of in vivo amyloid fibrils. This work will be conducted with the facilities and resources available at the Francis Bitter Magnet Lab (FBML) at the Massachusetts Institute of Technology (MIT) and will provide opportunity for significant training in solid-state NMR and amyloid structural biology under the mentorship of my sponsor, Professor Mei Hong, who is an expert in biomolecular solid-state NMR and has mentored many successful scientists before me. Completion of the proposed studies and training plan will allow me to grow as an independent scientist, a mentor, and a communicator, with the goal of pursuing a career as a principle investigator at a major research institution. Finally, this work will provide the first molecular insights into the dynamic domains of AD tau fibrils and the isoform mixing pattern within them, which should inform future development of AD therapies.