Measurement of Angstrom to Nanometer Molecular Distances with 19F Nuclear Spins by EPR/ENDOR Spectroscopy.

Spectroscopic and biophysical methods for structural determination at atomic resolution are fundamental in studies of biological function. Here we introduce an approach to measure molecular distances in bio-macromolecules using F-19 nuclear spins and nitroxide radicals in combination with high-frequency (94 GHz/3.4 T) electron-nuclear double resonance (ENDOR). The small size and large gyromagnetic ratio of the F-19 label enables to access distances up to about 1.5 nm with an accuracy of 0.1-1 angstrom. The experiment is not limited by the size of the bio-macromolecule. Performance is illustrated on synthesized fluorinated model compounds as well as spin-labelled RNA duplexes. The results demonstrate that our simple but strategic spin-labelling procedure combined with state-of-the-art spectroscopy accesses a distance range crucial to elucidate active sites of nucleic acids or proteins in the solution state.