Oligomer Diversity during the Aggregation of the Repeat Region of Tau.

Magnus Kjaergaard,Tuomas P J Knowles,David Klenerman,Franziska Kundel,Georg Meisl,Alexander J Dear,Seema Qamar

doi:10.1021/acschemneuro.8b00250

Magnus Kjaergaard, Tuomas P J Knowles + Show 5 more

Open Access

https://doi.org/10.1021/acschemneuro.8b00250

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Abstract

The molecular mechanism of protein aggregation is of both fundamental and clinical importance as amyloid aggregates are linked to a number of neurodegenerative disorders. Such protein aggregates include macroscopic insoluble fibrils as well as small soluble oligomeric species. Time-dependent resolution of these species is prerequisite for a detailed quantitative understanding of protein aggregation; this remains challenging due to the lack of methods for detecting and characterizing transient and heterogeneous protein oligomers. Here we have used single molecule fluorescence techniques combined with mechanistic modeling to study the heparin-induced aggregation of the repeat region of tau, which forms the core region of neurofibrillary tangles found in Alzheimer’s disease. We distinguish several subpopulations of oligomers with different stability and follow their evolution during aggregation reactions as a function of temperature and concentration. Employment of techniques from chemical kinetics reveals that the two largest populations are structurally distinct from fibrils and are both kinetically and thermodynamically unstable. The first population is in rapid exchange with monomers and held together by electrostatic interactions; the second is kinetically more stable, dominates at later times, and is probably off-pathway to fibril formation. These more stable oligomers may contribute to other oligomer induced effects in the cellular environment, for example, by overloading protein quality control systems. We also show that the shortest growing filaments remain suspended in aqueous buffer and thus comprise a third, smaller population of transient oligomers with cross-β structure. Overall our data show that a diverse population of oligomers of different structures and half-lives are formed during the aggregation reaction with the great majority of oligomers formed not going on to form fibrils.

Highlights

Of proteins into large insoluble fibrils is a characteristic hallmark, and possibly a cause, of several neurodegenerative diseases such as Parkinson’s and Alzheimer’s diseases.[1]
In Alzheimer’s disease, two distinct types of protein aggregates are found in the brain post mortem: extracellular plaques composed of the amyloid-β peptide and neurofibrillary tangles composed of the protein tau
We showed that tau oligomers are populated at low concentrations during the aggregation reaction and require an intramolecular conversion step before growth into filaments

Summary

Introduction

Of proteins into large insoluble fibrils is a characteristic hallmark, and possibly a cause, of several neurodegenerative diseases such as Parkinson’s and Alzheimer’s diseases.[1] In Alzheimer’s disease, two distinct types of protein aggregates are found in the brain post mortem: extracellular plaques composed of the amyloid-β peptide and neurofibrillary tangles composed of the protein tau. Of these two types of fibrils, the neurofibrillary tangles correlate more strongly with the extent of pathology, leading to an interest in the mechanism of their formation.[2]. We revisit single molecule FRET studies of tetra repeat (K18) tau aggregation by using the buffer conditions to resolve species of different stabilities

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