Significantly improved sensitivity of Q-band PELDOR/DEER experiments relative to X-band is observed in measuring the inter-coil distance of a leucine zipper motif peptide (GCN4-LZ)

摘要

Pulsed Electron Double Resonance (PELDOR)/Double Electron-Electron Resonance (DEER) spectroscopy is a very powerful structural biology tool in which the dipolar coupling between two unpaired electron spins (site-directed nitroxide spin labels) is measured. These measurements are typically conducted at X-band (9.4 GHz) microwave excitation using the 4-pulse DEER sequence and can often require up to 12+ hours of signal averaging for biological samples (depending upon spin label concentration). In this rapid report, we present for the first time, a substantial increase in DEER sensitivity obtained by collecting DEER spectra at Q-band (34 GHz), when compared to X-band. The huge boost in sensitivity (factor of 13) demonstrated at Q-band represents 169-fold decrease in data-collection time, reveals greatly improved frequency spectrum, higher quality distance data, and significantly increases sample throughput. Thus, the availability of Q-band DEER spectroscopy should have a major impact on structural biology studies using site-directed spin labeling EPR techniques.