Appraisal of role of the polyanionic inducer length on amyloid formation by 412-residue 1N4R Tau protein: A comparative study

Abstract

In many neurodegenerative diseases, formation of protein fibrillar aggregates has been observed as a major pathological change. Neurofibrillary tangles, mainly composed of fibrils formed by the microtubule-associated protein; Tau, are a hallmark of a group of neurodegenerative diseases such as Alzheimer's disease. Tau belongs to the class of natively unfolded proteins and partially folds into an ordered β-structure during aggregation. Polyanionic cofactors such as heparin are commonly used as inducer of Tau aggregation in vitro. The role of heparin in nucleation and elongation steps during Tau fibril formation is not fully understood. In the current study, aggregation kinetics as well as structure of Tau amyloid fibrils, by using the 1N4R isoform, have been reproducibly determined in the presence of heparin and the shorter molecule; enoxaparin. The kinetic studies demonstrated that heparin (not enoxaparin) efficiently accelerates Tau amyloid formation and revealed, mechanistically, that the molecular weight of the inducer is important in accelerating amyloidogenesis. The kinetic parameter values of Tau amyloid aggregation, especially, the amyloid aggregation extent, were relatively different in the presence of heparin and enoxaparin, at various stoichiometries of the inducers binding. Also, based on the results, obtained from CD, FTIR, AFM and XRD studies, it may be suggested that the inducer length plays a critical role mainly in the nucleation process, so that it determines that oligomers lie on or off the pathway of Tau fibrillization. The biochemical results herein suggest that the chemical environment of the extracellular matrix as well as localization of distinct glycosaminoglycans may influence deposition behavior of Tau amyloidosis.

Amyloidogenesis of Tau protein

“…However, out of all polyanionic inducers of Tau aggregation, heparin is the most frequently studied and considerably relevant for the physiological conditions, and is therefore the one attracting most attention. Heparin fractions composed of sufficiently long chains are known to be potent polyanionic inducers of Tau fibrillization, which contrasts with the behavior of shorter forms of this glycosaminoglycan . Apart from providing compensation of electric charges, heparin chains may act as flexible molecular rulers with periodicity matching that of the protein partner .…”

“…Heparin fractions composed of sufficiently long chains are known to be potent polyanionic inducers of Tau fibrillization, which contrasts with the behavior of shorter forms of this glycosaminoglycan. 105,117 Apart from providing compensation of electric charges, heparin chains may act as flexible molecular rulers with periodicity matching that of the protein partner. 105,118 Ramachandran and Udgaonkar 119 have shown in their study on four repeat domain of Tau (Tau4RD) that the heparin effect sets in very early in the course of aggregation by promoting binding of two Tau monomers and subsequent formation of an aggregation-prone dimer.…”

Kinetic and thermodynamic study of beta-Boswellic acid interaction with Tau protein investigated by surface plasmon resonance and molecular modeling methods

“…The complex formation between Tau and BBA leads to a variation in the Tau protein CD curve comparing with its unbound form in which one positive band around 193 appears which shows that the BBA binding leads to an increase in the α-helical structure of the Tau protein. 36 The calculated percentage of random coil and β-sheet in unbound Tau solution was 42.0% and 27.9%, respectively. After BBA (5×10 -6 M) addition, the random coil and β-sheet was 40.7% and 24.9%, respectively.…”

Cannabidiol Inhibits Tau Aggregation In Vitro

“…Proteins were further purified using the Ni-NTA column (Amersham BioSciences, Amersham, UK). After rinsing the columns with a 20 mM Imidazole, 20 mM Tris-HCl, PH 8 (4 times), Fractions of interest were collected in a buffer (6 M Imidazole, 20 mM Tris-HCl) [ 21 ]. The concentration of purified tau protein was measured using a UV-visible spectrophotometer (Varian bio-100) at OD 280 nm with excitation coefficient of tau protein 7700 M −1 cm −1 in the Beer-Lambert formula, and the purity was further assessed with SDS–PAGE.…”