The Global Analysis of DEER Data

Abstract

Previously, global analysis has been successfully used to analyze both continuous wave and saturation transfer EPR data1-3. In this work, algorithms have been developed for the global analysis of DEER data. Applications include the analysis of DEER data collected at multiple frequencies or multiple timescales. Analysis of DEER data from the soluble protein CDB3 (MW ≈ 90 kD) has shown that the background DEER signal is not well-fit by an exponential decay due to the large size of the CDB3 dimer. As a result, background correction with an exponential decay prior to analysis results in a poor fit to the data. An algorithm has been developed which explicitly fits the background signal with the radius of the molecule (assuming it is spherical) and the spin concentration as parameters. Using this approach, excellent fits to DEER data can be obtained without prior background correction. Also, DEER data can be globally analyzed to determine changes in the relative populations of components of the distance distribution as a function of experimental conditions. For example, DEER has been previously used to study the structural effects of a proline to arginine mutation at residue 327 of CDB3. Intradimer distances in spin-labelled wild type CDB3 can be fit using a single component distance distribution4. The same measurements on P327R CDB3 indicate the mutation induces a second more disordered component in the distance distribution5. The global analysis of DEER data collected for multiple spin-labelling sites in both the WT and P327R background is being used to further test this two-component model. Supported by NIH GM 080513. 1. Hustedt and Beth, BJ 69:1409–1423 (1995). 2. Hustedt et al., BJ 64:614–621 (1993). 3. Hustedt et al., BJ 72:1861–1877 (1997). 4. Zhou et al., Biochemistry 44:15115–15128 (2005). 5. Zhou et al., BJ 90:528A (2006).