title: Inter-spin distance determination using L-band (1-2 GHz) non-adiabatic rapid sweep electron paramagnetic resonance (NARS EPR).
abstract: Site-directed spin-labeling electron paramagnetic resonance (SDSL EPR) provides insight into the local structure and motion of a spin probe strategically attached to a molecule. When a second spin is introduced to the system, macromolecular information can be obtained through measurement of inter-spin distances either by continuous wave (CW) or pulsed electron double resonance (ELDOR) techniques. If both methodologies are considered, inter-spin distances of 8-80 Å can be experimentally determined. However, there exists a region at the upper limit of the conventional X-band (9.5 GHz) CW technique and the lower limit of the four-pulse double electron-electron resonance (DEER) experiment where neither method is particularly reliable. The work presented here utilizes L-band (1.9 GHz) in combination with non-adiabatic rapid sweep (NARS) EPR to address this opportunity by increasing the upper limit of the CW technique. Because L-band linewidths are three to seven times narrower than those at X-band, dipolar broadenings that are small relative to the X-band inhomogeneous linewidth become observable, but the signal loss, due to the frequency dependence of the Boltzmann factor, has made L-band especially challenging. NARS has been shown to increase sensitivity by a factor of five, and overcomes much of this loss, making L-band distance determination more feasible. Two different systems are presented, and distances of 18-30 Å have been experimentally determined at physiologically relevant temperatures. Measurements are in excellent agreement with a helical model and values determined by DEER.
authors: National Biomedical EPR Center, Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA. akittell@mcw.edu
authors: Aaron W
authors: AW
authors: Kittell
authors: Eric J
authors: EJ
authors: Hustedt
authors: James S
authors: JS
authors: Hyde
mesh_terms: D016880:Anisotropy; D017122:Bacteriophage T4 / Q000737:chemistry / Q000201:enzymology / Q000235:genetics; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D016018:Least-Squares Analysis; D008958:Models, Molecular; D009113:Muramidase / Q000032:analysis / Q000235:genetics; D009154:Mutation; D017433:Protein Structure, Secondary; D059629:Signal-To-Noise Ratio; D013696:Temperature
chemical_list: D009113:Muramidase