Nitroxide spin labels: fabulous spy spins for biostructural EPR applications

Characterizing proteins in action requires appropriate biophysical techniques sensitive to protein motions. One of the technique dedicated to monitor protein dynamics is Site-Directed Spin Labelling combined with EPR spectroscopy (SDSL-EPR). The main purpose of this chapter is to describe and illustrate the different strategies based on the use of nitroxide spin labels either as reporters or as a means to measure inter-label distances. The complementarity of these different approaches to answer biological questions will be addressed. The objective is also to give non-specialist readers an overview of the recent developments in the field of SDSL-EPR dedicated to the study of protein dynamics. A particular emphasis will be devoted to describe the design and application of new nitroxide spin labels that allow overcoming the limitations of the classical ones.