Conformational fingerprinting of tau variants and strains by Raman spectroscopy

Anna Crisford,Bradley T Hyman,Martin Margittai,George Devitt,Amrit Mudher,Caitlin Commins,Hilary A Weismiller,William Rice,Zhanyun Fan,Sumeet Mahajan

doi:10.1039/d1ra00870f

Abstract

Tauopathies are a group of disorders in which the deposition of abnormally folded tau protein accompanies neurodegeneration. The development of methods for detection and classification of pathological changes in protein conformation are desirable for understanding the factors that influence the structural polymorphism of aggregates in tauopathies. We have previously demonstrated the utility of Raman spectroscopy for the characterization and discrimination of different protein aggregates, including tau, based on their unique conformational signatures. Building on this, in the present study, we assess the utility of Raman spectroscopy for characterizing and distinguishing different conformers of the same protein which in the case of tau are unique tau strains generated in vitro. We now investigate the impact of aggregation environment, cofactors, post-translational modification and primary sequence on the Raman fingerprint of tau fibrils. Using quantitative conformational fingerprinting and multivariate statistical analysis, we found that the aggregation of tau in different buffer conditions resulted in the formation of distinct fibril strains. Unique spectral markers were identified for tau fibrils generated using heparin or RNA cofactors, as well as for phosphorylated tau. We also determined that the primary sequence of the tau monomer influenced the conformational signature of the resulting tau fibril, including 2N4R, 0N3R, K18 and P301S tau variants. These results highlight the conformational polymorphism of tau fibrils, which is reflected in the wide range of associated neurological disorders. Furthermore, the analyses presented in this study provide a benchmark for the Raman spectroscopic characterization of tau strains, which may shed light on how the aggregation environment, cofactors and post-translational modifications influence tau conformation in vivo in future studies.

Highlights

Tauopathies are a group of disorders in which the deposition of abnormally folded tau protein accompanies neurodegeneration
We have previously demonstrated that Raman spectroscopy provides unique conformational signatures for brils generated from Bovine Serum Albumin (BSA), b2M and tau proteins in vitro.[21]
We have demonstrated that tau brils adopt different conformations based on the physiochemical properties of the aggregation environment, the cofactor used for aggregation, the monomer primary sequence, and the presence or absence of disease associated mutations

Summary

Introduction

Tauopathies are a group of disorders in which the deposition of abnormally folded tau protein accompanies neurodegeneration. Distinct clinical symptoms and affected neuroanatomical regions enable disease classi cation.[1] The molecular structure of the pathological tau in different tauopathies is variable with respect to several factors including isoform. Pathological inclusions in Alzheimer's disease (AD) contain brils composed of both three-repeat (3R) and four-repeat (4R) tau isoforms, whereas Pick's disease (PiD) brils contain 3R isoforms, and progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) brils contain 4R isoforms.[1] Like other amyloids, these tau brils contain an intermolecular cross-b-sheet core composed of amino acids primarily in the repeat-domain.[3] Structural variations in the loop and turn regions or the inclusion of different amino acids in the individual b-strands of the amyloid core result in distinct conformers/strains of assembled tau protein.

Results

Discussion

Conclusion