Characterization of Interactions Between Proteins Using Site-Directed Spin Labeling and Electron Par

Site-directed spin-labeling and the analysis of proteins by electron paramagnetic resonance spectroscopy provides a powerful tool for identifying sites of contact within protein complexes at the resolution of aminoacyl side chains. Here we describe the method as we have used it to study interactions of proteins involved in export via the Sec secretory system in Escherichia coli . The method is amendable to the study of most protein interactions.