Multifrequency electron spin resonance study of the dynamics of spin labeled T4 lysozyme.
Continuous-wave electron spin resonance (cwESR) experiments combined with site-directed spin labeling (SDSL) techniques are a rich source of information about the local structure and dynamics of biomolecules in native-like environments [6, 10, 16]. Partly owing to its high sensitivity and the relative ease with which biomolecules can be systematically labeled at almost any desired location (e.g., by introducing cysteine mutations in proteins), ESR plays an increasingly important role in studies of proteins , nucleic acids , and membrane systems . An exciting aspect of cw-ESR is the extreme sensitivity of the technique to the details of the dynamical processes occurring at the molecular level. Cw-ESR spectra are sensitive to dynamics over a broad range of time scales, from hundreds of picoseconds to tens of nanoseconds, depending on the strength of the constant magnetic field or the corresponding microwave frequency. While the slower end of this temporal range is routinely covered by lower fields/frequencies, like the most commonly used X-band, the faster end has recently become accessible as a result of vigorous