Orientation selective DEER measurements on vinculin tail at X-band frequencies reveal spin label orientations

Autor(en): Abe, Christoph
Klose, Daniel 
Dietrich, Franziska
Ziegler, Wolfgang H.
Polyhach, Yevhen
Jeschke, Gunnar
Steinhoff, Heinz-Juergen 
Stichwörter: Biochemical Research Methods; Biochemistry & Molecular Biology; BIOMACROMOLECULES; COMPREHENSIVE SOFTWARE PACKAGE; DISORDERED SOLIDS; DISTANCE MEASUREMENTS; ELECTRON-PARAMAGNETIC-RESONANCE; EPR SPECTROSCOPY; NITROXIDE BIRADICALS; Orientation selective DEER; PELDOR; Physics; Physics, Atomic, Molecular & Chemical; SITE; Site-directed spin labeling; Spectroscopy
Erscheinungsdatum: 2012
Volumen: 216
Startseite: 53
Seitenende: 61
Double electron electron resonance (DEER) spectroscopy has been established as a valuable method to determine distances between spin labels bound to protein molecules. Caused by selective excitation of molecular orientations DEER primary data also depend on the mutual orientation of the spin labels. For a doubly spin labeled variant of the cytoskeletal protein vinculin tail strong orientation selection can be observed already at X-band frequencies, which allows us to reduce the problem to the relative orientation of two molecular axes and the spin-spin axis parameterized by three angles. A full grid search of parameter space reveals that the DEER experiment introduces parameter-space symmetry higher than the symmetry of the spin Hamiltonian. Thus, the number of equivalent parameter sets is twice as large as expected and the relative orientation of the two spin labels is ambiguous. Except for this inherent ambiguity the most probable relative orientation of the two spin labels can be determined with good confidence and moderate uncertainty by global fitting of a set of five DEER experiments at different offsets between pump and observer frequency. The experiment provides restraints on the angles between the z axis of the nitroxide molecular frame and the spin-spin vector and on the dihedral between the two z axes. When using the same type of label at both sites, assignment of the angle restraints is ambiguous and the sign of the dihedral restraint is also ambiguous. (C) 2012 Elsevier Inc. All rights reserved.
ISSN: 10907807
DOI: 10.1016/j.jmr.2011.12.024

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