Cryo-EM structures of tau filaments from Alzheimer\u2019s disease with PET ligand APN-1607

Yang Shi,Alexander Epstein,Michel Goedert,Alexey G Murzin,Paul Tempest,Sjors H W Scheres,Holly J Garringer,Ruben Vidal,Ming-Kuei Jang,Bernardino Ghetti,Benjamin Falcon,Makoto Higuchi,Kathy L Newell,Naruhiko Sahara,Jonathan Machin

doi:10.1007/s00401-021-02294-3

Abstract

Tau and Aβ assemblies of Alzheimer’s disease (AD) can be visualized in living subjects using positron emission tomography (PET). Tau assemblies comprise paired helical and straight filaments (PHFs and SFs). APN-1607 (PM-PBB3) is a recently described PET ligand for AD and other tau proteinopathies. Since it is not known where in the tau folds PET ligands bind, we used electron cryo-microscopy (cryo-EM) to determine the binding sites of APN-1607 in the Alzheimer fold. We identified two major sites in the β-helix of PHFs and SFs and a third major site in the C-shaped cavity of SFs. In addition, we report that tau filaments from posterior cortical atrophy (PCA) and primary age-related tauopathy (PART) are identical to those from AD. In support, fluorescence labelling showed binding of APN-1607 to intraneuronal inclusions in AD, PART and PCA. Knowledge of the binding modes of APN-1607 to tau filaments may lead to the development of new ligands with increased specificity and binding activity. We show that cryo-EM can be used to identify the binding sites of small molecules in amyloid filaments.

Highlights

Of a small number of soluble proteins into insoluble amyloid filaments underlies the majority of age-related neurodegenerative diseases [20]
All six tau isoforms assemble in Alzheimer’s disease (AD) and chronic traumatic encephalopathy (CTE), but only four-repeat tau forms inclusions in progressive supranuclear palsy (PSP), globular glial tauopathy (GGT) and corticobasal degeneration (CBD); Pick’s disease (PiD) is a three-repeat tau proteinopathy
Tau filaments were extracted from the frontal cortex of neuropathologically confirmed cases of AD with sarkosyl or by affinity chromatography [28]

Summary

Introduction

Of a small number of soluble proteins into insoluble amyloid filaments underlies the majority of age-related neurodegenerative diseases [20]. Tau is the most commonly affected of these proteins All six tau isoforms assemble in AD and CTE, but only four-repeat tau forms inclusions in PSP, GGT and CBD; PiD is a three-repeat tau proteinopathy. Amyloid dyes and antibodies that label tau assemblies in post mortem brains have been available for many years, PET ligands that detect tau inclusions in living subjects have only recently been developed. It has been shown that second-generation tau PET probe 18F-APN-1607, called 18F-PMPBB3 (propanol modification of PBB3), a compound with high metabolic stability, labels brain regions with abundant tau inclusions in AD and PSP [26, 46]. We used cryoEM structure determination to identify the binding sites of APN-1607 in PHFs and SFs from AD

Materials and methods

Results and discussion

Conclusion