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

Abstract

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 19F 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 19F label enables to access distances up to about 1.5 nm with an accuracy of 0.1–1 Å. 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.