Biophysical Characterization of Covalently Modified Protein Tau: Oligomers, Aggregation, and Tubulin Interactions

Abstract

The molecular interactions that drive the onset and spread of Alzheimer's disease (AD) remain poorly understood. In AD, tau neurofibrillary tangles correlate with cognitive decline and have historically been associated with tau's toxicity. Recently, tau oligomers have been implicated as stable toxic subunits that contribute to the formation of paired helical filaments and eventual neurofibrillary tangles. Covalently modified tau is a major component of neurofibrillary tangles and plays a significant role in tau's ability to dissociate from microtubules, aggregate, and become toxic. Elucidating the effects of covalent modifications on oligomer formation could aide our understanding of the molecular mechanisms behind tau's toxicity. The complexity of tau, partially due to its intrinsically disordered nature, allows for phosphorylation, acetylation, and succinylation to occur at multiple sites and influence the physiological and pathological roles of tau. Specific residue modifications can play a major role in modulating tau function and aggregation. This has led to the use of mimics in cell, mouse, and in-vitro models of tau pathology. Site-specific mimics of phosphorylation, acetylation, and succinylation can aide our ability to biophysically characterize the effect of covalently modified tau on oligomer formation, aggregation propensity, and tubulin interactions; Ultimately aiding our understanding of tau function and structure. We apply nuclear magnetic resonance, fluorescence, and light scattering to show that covalently modified tau mimics of phosphorylation, acetylation, and succinylation perturb tau-T2R interactions (a model of tau-tubulin interactions), induce filament formation, and form stable toxic oligomers with different levels of efficiency. Our results reinforce phosphorylation as a contributor to filament formation, acetylation as a driver of oligomer formation, and introduces tau succinylation as a novel modifier of tau structure and function.