Spin labeling and characterization of tau fibrils using electron paramagnetic resonance (EPR)

Abstract

Template-assisted propagation of Tau fi brils is essential for the spreading of Tau pathology in Alzheimer’s disease. In this process, small seeds of fi brils recruit Tau monomers onto their ends. The physical properties of the fi brils play an important role in their propagation. Here, we describe two different electron paramagnetic resonance (EPR) techniques that have provided crucial insights into the structure of Tau fi brils. Both techniques rely on the site-directed introduction of one or two spin labels into the protein monomer. Continuous-wave (CW) EPR provides information on which amino acid residues are contained in the fi bril core and how they are stacked along the long fi bril axis. Double electron–electron resonance (DEER) determines distances between two spin labels within a single protein and hence provides insights into their spatial arrangement in the fi bril cross section. Because of the long distance range accessible to DEER (~2–5 nm) populations of distinct fi bril conformers can be differentiated.