Field-domain rapid-scan EPR at 240GHz for studies of protein functional dynamics at room temperature.

Price, Brad D; Sojka, Antonín; Maity, Shiny; Chavez, I Marcelo; Starck, Matthieu; Wilson, Maxwell Z; Han, Songi; Sherwin, Mark S

Abstract

We present field-domain rapid-scan (RS) electron paramagnetic resonance (EPR) at 8.6T and 240GHz. To enable this technique, we upgraded a home-built EPR spectrometer with an FPGA-enabled digitizer and real-time processing software. The software leverages the Hilbert transform to recover the in-phase (I) and quadrature (Q) channels, and therefore the raw absorptive and dispersive signals, χ and χ , from their combined magnitude (I +Q ). Averaging a magnitude is simpler than real-time coherent averaging and has the added benefit of permitting long-timescale signal averaging (up to at least 2.5×10 scans) because it eliminates the effects of source-receiver phase drift. Our rapid-scan (RS) EPR provides a signal-to-noise ratio that is approximately twice that of continuous wave (CW) EPR under the same experimental conditions, after scaling by the square root of acquisition time. We apply our RS EPR as an extension of the recently reported time-resolved Gd-Gd EPR (TiGGER) [Maity et al., 2023], which is able to monitor inter-residue distance changes during the photocycle of a photoresponsive protein through changes in the Gd-Gd dipolar couplings. RS, opposed to CW, returns field-swept spectra as a function of time with 10ms time resolution, and thus, adds a second dimension to the static field transients recorded by TiGGER. We were able to use RS TiGGER to track time-dependent and temperature-dependent kinetics of AsLOV2, a light-activated phototropin domain found in oats. The results presented here combine the benefits of RS EPR with the improved spectral resolution and sensitivity of Gd chelates at high magnetic fields. In the future, field-domain RS EPR at high magnetic fields may enable studies of other real-time kinetic processes with time resolutions that are otherwise difficult to access in the solution state. [Abstract copyright: Published by Elsevier Inc.]

Citation

Price, B. D., Sojka, A., Maity, S., Chavez, I. M., Starck, M., Wilson, M. Z., Han, S., & Sherwin, M. S. (2024). Field-domain rapid-scan EPR at 240GHz for studies of protein functional dynamics at room temperature. Journal of Magnetic Resonance, 366, Article 107744. https://doi.org/10.1016/j.jmr.2024.107744

• Journal Article Type: Article
• Acceptance Date: Jul 24, 2024
• Online Publication Date: Jul 27, 2024
• Publication Date: 2024-09
• Deposit Date: Aug 29, 2024
• Publicly Available Date: Aug 29, 2024
• Journal: Journal of Magnetic Resonance
• Print ISSN: 1090-7807
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 366
• Article Number: 107744
• DOI: https://doi.org/10.1016/j.jmr.2024.107744
• Keywords: Rapid-scan, Time-resolved kinetics, Terahertz, Hilbert transform, Protein dynamics, Magnetic resonance, High magnetic fields and frequencies, Electron paramagnetic resonance, ESR, EPR
• Public URL: https://durham-repository.worktribe.com/output/2768007