Identifying conformational changes with site-directed spin labeling

Site-direct spin labeling combined with electron paramagnetic resonance (EP R) spectroscopy is a powerful tool for detecting structural changes in prot eins. This review provides examples that illustrate strategies for interpre ting the data in terms of specific rearrangements in secondary and tertiary structure. The changes in the mobility and solvent accessibility of the sp in label side chains, and in the distances between spin labels, report (i) rigid body motions of alpha-helices and beta-strands (ii) relative movement s of domains and (iii) changes in secondary structure. Such events can be m onitored in the millisecond timescale, making it possible to follow structu ral changes during function. There is no upper limit to the size of protein s that can be investigated, and only 50-100 picomoles of protein are requir ed. These features make site-directed spin labeling an attractive approach for the study of structure and dynamics in a wide range of systems.