EPR distance measurements in deuterated proteins

Pulsed electron double resonance technique, also known as double electron-electron resonance, jointly with site-directed spin labeling (SDSL) have been used extensively for studying structures and structural change. During the last decades, significant enhancements have been made by optimization of the experimental protocols, introducing new techniques for artifact suppression, and developing data analysis programs for extracting more reliable distance distributions. However, the distance determination by pulsed electron paramagnetic resonance is still facing some limitations, especially when studying spin-labeled proteins, due mainly to the fast relaxation time that imposes severe limitations on the maximum distances measurable and upon the sensitivity of such experiments. In the present work, we demonstrate the impact of the deuteration of the underlying protein, in addition to the solvent, on relaxation times, sensitivity, and on distance measurements.