Rapid Analysis of DEER Signals Including Short Distances

Double electron electron resonance (DEER) spectroscopy is an important technique to measure distance distributions <i>P</i>(<i>r</i>) for studying protein structures and protein-protein interactions. DEER data analysis can at times become challenging due to the lack of a detailed analytical signal expression or numerical methods with rapid computation time. We have derived an analytical expression κ_FULL, which includes both the pseudo-secular dipolar coupling (PSDC) and the finite pulse effects, especially important for shorter distances. Analyses of experiments by κ_FULL yield accurate and consistent <i>P</i>(<i>r</i>) values for three DEER nitroxide-rulers with distances (<i>r</i>_AVG) in the range of 15 to 32 Å, while the current standard analysis produces erroneous results for <i>r</i>_AVG < 20 Å. Computation times for deriving <i>P</i>(<i>r</i>) vary between 1 min and 4 min, which is usually much shorter than previous methods that include pseudo-secular and other effects. The expression can be applied to all types of DEER spin probes with little or no modifications.