Signature of an aggregation-prone conformation of tau

Neil A Eschmann,Jack H Freed,Joan-Emma Shea,Yasar Akdogan,Elka R Georgieva,Maxime D Rappaport,Pritam Ganguly,Songi Han,Peter P Borbat

doi:10.1038/srep44739

Abstract

The self-assembly of the microtubule associated tau protein into fibrillar cell inclusions is linked to a number of devastating neurodegenerative disorders collectively known as tauopathies. The mechanism by which tau self-assembles into pathological entities is a matter of much debate, largely due to the lack of direct experimental insights into the earliest stages of aggregation. We present pulsed double electron-electron resonance measurements of two key fibril-forming regions of tau, PHF6 and PHF6*, in transient as aggregation happens. By monitoring the end-to-end distance distribution of these segments as a function of aggregation time, we show that the PHF6(*) regions dramatically extend to distances commensurate with extended β-strand structures within the earliest stages of aggregation, well before fibril formation. Combined with simulations, our experiments show that the extended β-strand conformational state of PHF6(*) is readily populated under aggregating conditions, constituting a defining signature of aggregation-prone tau, and as such, a possible target for therapeutic interventions.

Highlights

That pack to form the β-sheet structured core of mature tau fibrils[16,20,21,22]
Some groups have proposed further evidence supporting the hypothesis that heparin is capable of altering the conformational state of tau, but there is no direct experimental report to date on the changes of tau conformations prior to fibrillization[34,35,36,37]
The emerging concept is that the relatively compact conformation found around the hexapeptide regions of tau in solution state may play a role in hindering tau fibrillization, while there has been a previous report on persistent local structures of type I β-turns near the same hexapeptide region of tau protein in solution, whose role in preventing pathological fibrillization has been speculated[39]

Summary

Introduction

That pack to form the β-sheet structured core of mature tau fibrils[16,20,21,22]. The PHF6(*) repeat domains of tau stack into highly ordered, neat, β-sheets up the fibril axis, in which these hexapeptide segments adopt fully extended conformations[6,23]. When looking to identify conformational transformation that tau may undergo, we focus on distance changes across sites that are flanking the PHF6(*) region, of stable tau proteins and model peptides in solution state, before and after initiating aggregation. We employ site-directed mutagenesis to cysteine and spin labeling (SDSL) of two sites flanking the PHF6(*) region to perform double electron-electron resonance (DEER) measurements to extract distance and distance distribution as a function of aggregation time. We set out to test a new paradigm for the aggregation of IDPs, namely that distinct conformational ensembles of IDPs represent distinct states, such as the “stable” vs. “aggregation-prone” states of Tau

Methods

Results

Conclusion