Fig. 4. EPR of singly and doubly spin-labeled Tau derivatives gives access to Tau side-chain dynamics and intramolecular distance information.

(A) Local side-chain dynamics accessed by cw EPR of 28 μM singly spin-labeled Tau derivatives: Rotational correlation times τcorr determined in the absence (dark gray) and presence (light gray) of 56 μM Hsp90 and respective changes Δτcorr (purple/pink) are shown. Arrows indicate a decrease (pink) or increase (purple) in side-chain mobility at the respective site. (B) Intramolecular distance information obtained by DEER spectroscopy with doubly spin-labeled Tau derivatives: Effective modulation depths Δeff determined in the absence (dark gray) and presence (light gray) of Hsp90 and respective changes ΔΔeff (light/dark green) are shown. Arrows indicate a decrease (light green) or increase (dark green) in spin label separation.