Interpretation of dipolar EPR data in terms of protein structure

Abstract

Distances in proteins in the nanometer range can be measured by the combination of site-directed spin labeling and dipolar EPR. The primary data are related to the time evolution of spin label magnetization under the dipole–dipole interaction with other spin labels within the same or within the neighboring protein molecules. The information sought are conclusions on protein structure or structural changes. The link between primary data and these conclusions are distances between backbone atoms in the protein. We discuss which experimental conditions allow for the most precise data analysis in terms of distance distributions and describe techniques for such data analysis. Furthermore, methods are reviewed for prediction of conformational distribution of the spin label, which is required to infer backbone–backbone distances from label–label distances.