Resonance Raman Spectroscopic Measurements Delineate the Structural Changes that Occur during Tau Fibril Formation

Abstract

The aggregation of the microtubule-associated protein, tau, into amyloid fibrils is a hallmark of neurodegenerative diseases such as the tauopathies and Alzheimer's disease. Since monomeric tau is an intrinsically disordered protein and the polymeric fibrils possess an ordered cross-β core, the aggregation process is known to involve substantial conformational conversion besides growth. The aggregation mechanism of tau in the presence of inducers such as heparin, deciphered using probes such as thioflavin T/S fluorescence, light scattering, and electron microscopy assays, has been shown to conform to ligand-induced nucleation-dependent polymerization. These probes do not, however, distinguish between the processes of conformational conversion and fibril growth. In this study, UV resonance Raman spectroscopy is employed to look directly at signatures of changes in secondary structure and side-chain packing during fibril formation by the four repeat functional domain of tau in the presence of the inducer heparin, at pH 7 and at 37 °C. Changes in the positions and intensities of the amide Raman bands are shown to occur in two distinct stages during the fibril formation process. The first stage of UVRR spectral changes corresponds to the transformation of monomer into early fibrillar aggregates. The second stage corresponds to the transformation of these early fibrillar aggregates into the final, ordered, mature fibrils and during this stage; the processes of conformational conversion and the consolidation of the fibril core occur simultaneously. Delineation of these secondary structural changes accompanying the formation of tau fibrils holds significance for the understanding of generic and tau-specific principles of amyloid assembly.

Rescue from tau-induced neuronal dysfunction produces insoluble tau oligomers

“…This technique interrogates the vibrations of bonds in molecules generating characteristic spectral profiles. It allows insight into the chemical structure and interactions between different groups and side chains in proteins, providing an analysis of their secondary structure 42 and aggregated state 43 . We hypothesized that the spectral profile of insoluble fractions generated from hTau flies in which the tau is primarily monomeric, would differ from that of Li-treated hTau flies in which tau oligomers form.…”

Secondary structures transition of tau protein with intrinsically disordered proteins specific force field

“…[25][26][27][28] Tau is one of the major pathophysiologically relevant proteins in the AD, which hyperphosphorylated Tau aggregates into paired helical filaments (PHFs) and further causes neurodegeneration. [31,32] Recent researches show that the formation of PHFs is based on structural transitions from random coil to β-sheet structure. [31,32] Recent researches show that the formation of PHFs is based on structural transitions from random coil to β-sheet structure.…”

“…[29,30] The progressive accumulation of neurofibrillary tangles (NFTs) is one of the neuropathological hallmarks of the AD which the core of these PHFs is belonging to the repeat domains and its flanking regions. [31,32] Recent researches show that the formation of PHFs is based on structural transitions from random coil to β-sheet structure. [33][34][35] These minimal interaction motifs with local β-structure are a focus on the beginning of the R2 and the R3.…”

Advanced imaging of tau pathology in Alzheimer Disease: New perspectives from super resolution microscopy and label‐free nanoscopy

“…FT‐IR also detects β‐sheet content in Tau filaments with diverse conformation (Frost et al, ). Likewise, UV Raman Resonance (UVRR) spectroscopy has been applied to investigate the aggregation of recombinant Tau in vitro , yielding interesting results on the complexity of the dynamic of Tau aggregation (Ramachandran et al, ). These results indicate that this technique is potentially applicable to the analysis of the variety of Tau aggregates conformations associated with different Tau lesions.…”