Conformational motions of proteins are the basis of their function – proteins have to be able to move in order to fulfill their role. Our lab is interested in quantifying these motions, that is, the conformational landscapes of proteins and their changes upon interaction with ligands and other proteins. As primary technique, we use Double Electron-Electron Resonance (DEER) spectroscopy, a form of Electron Paramagnetic Resonance (EPR) spectroscopy. Using DEER, we directly measure distances and distance distributions within proteins, without the need for crystallizing the protein. With the data, we then build models that capture a protein’s intrinsic flexibility and the structural changes induced by ligands or binding partners. We study a variety of soluble and membrane proteins.