Cryo-EM structural analyses reveal diverse porous structures in brain-derived tau oligomers

Misfolding and aggregation of tau into oligomers and neurofibrillary tangles are associated with Alzheimer's disease and related dementia (ADRD). Misfolded oligomeric species are widely believed to play a critical role in both disrupting cellular functions and propagating protein misfolding between cells. Characterization of the misfolded oligomers is crucial for understanding the mechanisms underlying protein aggregation and its role in disease pathogenesis. However, structural characterization of these misfolded oligomers has proven challenging due to their transient and heterogeneous nature. Here we report structural features of brain-derived tau oligomers extracted from Alzheimer's brains. Initial screening using negative staining transmission electron microscopy (TEM) and atomic force microscopy (AFM) reveal that tau (2N4R) forms a diverse array of pore-like oligomers with a diameter of 5-20 nm and a height of ∼2-8 nm. Higher-resolution structural analyses using cryo-EM on oligomers with diameters of 10-20 nm revealed the presence of two distinct layers within the pore-like structures, resolved at 2.5-4 Å. Our structural studies support the hypothesis that misfolded proteins may function as pore-forming toxins, potentially disrupting cellular membranes.