Robustness and sensitivity of Gd(III)-Gd(III) double electron electron resonance (DEER) measurements: comparative study of high-frequency EPR spectrometer designs and spin label variants

Elena Mihaela Mocanu, Yasmin Ben-Ishay, Lydia Topping, Stuart Ronan Fisher, Robert Iain Hunter, Xun-Cheng Su, Stephen Butler, Graham Murray Smith, Daniella Goldfarb, Janet Eleanor Lovett*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

In this paper we explore the robustness and sensitivity of Gd(III)-Gd(III) double electron-electron resonance (DEER) distance measurements in proteins for different spectrometer designs and a three spin labels. To do this a protein was labelled at the same two positions with Gd(III) spin labels and measurements were performed on two home-built high-frequency (W-band, ~95 GHz) EPR spectrometers with different design approaches, and a commercial Q-band spectrometer. The first W-band measurement approach uses a conventional, narrow band single mode cavity, while the second approach uses a broad band non-resonant induction mode sample holder. Both systems incorporate advanced arbitrary waveform generators (AWGs) that give flexibility over excitation bandwidth. We use three DOTA-like Gd(III) spin labels, Gd.C12, Gd.DO3A and the new Gd.L1, conjugated to the model protein calmodulin. We compare measurements taken by including or excluding the excitation of the Gd(III) central transition. The advantages and disadvantages of the EPR spectrometers for the measurement of Gd(III)-Gd(III) DEER are discussed in terms of the robustness of the resulting distance distribution width, absolute and concentration sensitivity, sample handling, ease of use, and flexibility of measurement.
Original languageEnglish
Number of pages21
JournalApplied Magnetic Resonance
VolumeEarly View
Early online date3 Jan 2025
DOIs
Publication statusE-pub ahead of print - 3 Jan 2025

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