Application of site-directed spin labeling combined with electron paramagnetic resonance to protein structure studies

Site-directed spin labeling(SDSL) combined with electron paramagnetic resonance(EPR) spectroscopy is a powerful tool for detecting structure of proteins.Application of SDSL is experiencing a stage of rapid evolution.In this review the application of SDSL-EPR to determining secondary and tertiary structure of proteins,such as the changes in the mobility and solvent accessibility of the spin labeled side chains,membrane protein topography,electrostatic potentials,and the orientation of proteins at membrane surfaces,inter-residue distances and time-resolved changes in protein is illustrated. These events can be monitored in the millisecond or nanosecond time-scale,making it possible to follow structural changes during functioning.There is no upper limit to the size of proteins investigated,and sometimes only 50-100 picomoles(pmol) of protein are required.These features make site-directed spin labeling an attractive approach for the study of structure and dynamics of a wide range of systems.