25-30 August 2019
Henry Ford Building
Europe/Berlin timezone

Molecular distances using electron and <sup>19</sup>F nuclear spins at high EPR fields (3.4 T/ 94 GHz): from model systems to biological applications

Not scheduled
4h
Harnack House and Henry Ford Building

Harnack House and Henry Ford Building

Board: 297
Poster Posters

Speaker

Dr Andreas Meyer (Max-Planck-Institute for Biophysical Chemistry)

Description

One of the main application fields of EPR in biological samples is the investigation of paramagnetic centers (like metal ions or amino acid radicals) in proteins. Electron-nuclear double resonance (ENDOR) allows obtaining information about naturally occurring, nuclear spins (1H, 14N, …) in the immediate neighborhood of such electron spin centers. Interactions with remote nuclei (≥ 7 Å) are often poorly resolved owed to the weakness of the interaction. The strongest coupling is typically exerted by 1H nuclei. However, their ubiquity in biological macromolecules leads to crowding of 1H ENDOR spectra. 19F nuclei interact almost as strongly with electron spins as 1H does, and it is often possible to replace 1H by 19F nuclei due to the bioisosterism of the two atoms. We introduce here 19F nuclei as spin labels for ENDOR at high EPR fields (3.4 T/94 GHz), where the 19F resonance frequency is reasonably (> 8 MHz) separated from all other nuclear resonances. The feasibility of this approach is shown at three stages. First, it is demonstrated that couplings between a nitroxide radical and 19F nuclear spin are detectable for distances up to 15 Å on small, synthetic models. For r ≳ 6 Å distances are found well consistent with the point-dipole model. In a second set of experiments on spin labelled RNA duplexes, data of comparable quality could be obtained. Finally, first applications of the method are shown on 19F labelled E. coli ribonucleotide reductase, providing geometrical information about the intermediate tyrosyl radical Y356● in the long range radical transfer pathway of this enzyme. The results indicate that the method of 19F ENDOR could find application as a general tool in ESR spectroscopy for the intermediate distance range (~ 5 – 15 Å), as did PELDOR for the large distance range (~ 20 – 100 Å).

Primary authors

Dr Andreas Meyer (Max-Planck-Institute for Biophysical Chemistry) Dr Sebastian Dechert (Department of Chemistry, University of Göttingen) Prof. Claudia Höbartner (Institute of Organic Chemistry, University of Würzburg) Prof. Marina Bennati (Max-Planck-Institute for Biophysical Chemistry)

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