New limits of sensitivity of site-directed spin labeling electron paramagnetic resonance for membrane proteins

Site-directed spin labeling electron paramagnetic resonance is a biophysical technique based on the specific introduction of spin labels to one or more sites in diamagnetic proteins, which allows monitoring dynamics and water accessibility of the spin-labeled side chains, as well as nanometer distances between two (or more) labels. Key advantages of this technique to study membrane proteins are addressed, with focus on the recent developments which will expand the range of applicability. Comparison with other biophysical methods is provided to highlight the strength of EPR as complementary tool for structural biology. This article is part of a Special Issue entitled: Beyond the Structure-Function Horizon of Membrane Proteins edited by Ute Hellmich, Rupak Doshi and Benjamin McIlwain. •Site-directed spin labeling EPR is a complementary tool in structural biology.•Methods to extract dynamics and water accessibility of spin-labeled sites are presented.•Interspin distances identify proteins’ conformational changes and interactions.•Two examples of application on membrane proteins are provided.