Chapter 10: Applications of Nitroxide Spin Labels to Structural Biology

Spin labels have been used for more than three decades in site-directed spin labeling (SDSL) electron paramagnetic resonance (EPR) spectroscopy for protein structural biology studies. Though many of the original spin labels are still commonly used in the field, new advances have continually introduced novel nitroxide labels. Here we present an array of novel and commonly used nitroxide-based spin labels along with their properties, uses, strengths and weaknesses. We also present examples of their utility in the applications of EPR spectroscopy approaches to structural biology studies, which include protein structure, in the past five years and the expected future directions and needs in the evolving field of SDSL EPR spectroscopy.