Distance Determination in Proteins inside Xenopus laevis Oocytes by Double Electron−Electron Resonance Experiments

DEER (double electron-electron resonance) enables the observation of long-range dipole interactions (1.5-8 nm) between electron spin centers and has become a unique method for structural analysis of site-directed spin-labeled (SDSL) proteins. The method was applied to proteins inside eukaryotic cells, Xenopus laevis oocytes. DEER measurements of the oocytes, into which SDSL-ubiquitin derivates were injected, gave rise to interpretable signals and allowed us to perform in situ analyses of the interspin distances of the proteins.