UC Santa Barbara

In the Tauopathy subfamily of neurodegenerative diseases, the intrinsically disordered protein (IDP), Tau, undergoes a transition from its native disordered state into insoluble, pathological amyloid fibrils, such as those found in the neurofibrillary tangles of Alzheimer’s disease (AD). The mechanisms of Tau aggregation are still unclear, despite decades of research. This dissertation describes how Tau interacts with it surrounding environment and the cofactors that lead to its pathological aggregation. Chapter 1 provides an overview of disordered proteins, aggregation, Tau, neurodegeneration, and the biophysical techniques used throughout this manuscript. Chapter 2 describes the fibril structures formed by recombinant Tau when incubated with heparin, a polysulphated glycosaminoglycan, and how the structures are heterogeneous and dissimilar to the fibrils observed in AD. Chapter 3 investigates the nature of the interaction between Tau and the anionic cofactors routinely used to generate fibrils in vitro. The cofactors were found to be integral to the fibrils and stoichiometric quantities of cofactor were required to form the fibril. In Chapter 4, fragments of Tau were produced that were found to exist in pathological brain tissue. These proteolytic products of Tau that are observed in AD patients form potent, aggregation-prone fragments of Tau that may be involved in initiating aggregation of larger species of full-length Tau. In Chapter 5, shorter peptides of Tau are used to demonstrate the effect of a hereditary mutation (P301L) observed in chromosome 17 linked frontotemporal dementia and Parkinsonism (FTDP-17). The primary effect of the mutation, in a short peptide of Tau (HP301L), is to create a slower-moving hydration shell with a lower entropy than in the WT form. The lower entropy around the hydrophobic leucine makes the dehydration required for amyloid formation more energetically favorable, leading to higher aggregation propensity. Chapter 6 describes ongoing work to determine structure of the fibrils formed by the P301L peptide in Chapter 5. A structure is presented showing a fibril core at 4.6 Å resolution with a C2 symmetry composed of 2 hairpin-shaped protofilaments. Chapter 7 investigates the proline rich domain of Tau and its role in liquid liquid phase separation and identifies the SH3 domain as a binding partner that may be involved in the removal of Tau from microtubules. Chapter 8 suggests future directions for the field and outstanding questions from this body of work.