Slow dynamics of solid proteins – Nuclear magnetic resonance relaxometry versus dielectric spectroscopy

Danuta Kruk,Elzbieta Masiewicz,Milosz Wojciechowski,Malgorzata Florek-Wojciechowska,Lionel M Broche,David J Lurie

doi:10.1016/j.jmr.2020.106721

Abstract

1H Nuclear Magnetic Resonance (NMR) relaxometry and Dielectric Spectroscopy (DS) have been exploited to investigate the dynamics of solid proteins. The experiments have been carried out in the frequency range of about 10 kHz-40 MHz for NMR relaxometry and 10−2Hz-20 MHz for DS. The data sets have been analyzed in terms of theoretical models allowing for a comparison of the correlation times revealed by NMR relaxometry and DS. The 1H spin–lattice relaxation profiles have been decomposed into relaxation contributions associated with 1H–1H and 1H-14N dipole – dipole interactions. The 1H–1H relaxation contribution has been interpreted in terms of three dynamical processes of time scales of 10−6s, 10−7s and 10−8s. It has turned out that the correlation times do not differ much among proteins and they are only weakly dependent on temperature. The analysis of DS relaxation spectra has also revealed three motional processes characterized by correlation times that considerably depend on temperature in contrast to those obtained from the 1H relaxation. This finding suggest that for solid proteins there is a contribution to the 1H spin–lattice relaxation associated with a kind of motion that is not probed in DS as it does not lead to a reorientation of the electric dipole moment.

Highlights

Revealing the structure and dynamics of biological macromolecules is essential for understanding their biological function
The data for Lysozyme and Bovine Serum Albumin (BSA) are in good agreement with those reported in [65] at 302 K
The data are very similar for all proteins and only weakly dependent on temperature

Summary

Introduction

Revealing the structure and dynamics of biological macromolecules is essential for understanding their biological function. High resolution Nuclear Magnetic Resonance (NMR) spectroscopy is a leading method providing access to multi-dimensional protein structure and conformation [1,2,3]. The most powerful methods of probing slow dynamics of biomolecules are NMR relaxometry and Dielectric Spectroscopy (DS). Both methods provide information about molecular motion, their physical principles are very different: spin relaxation is a quantum–mechanical phenomenon reflecting time scales and mechanisms of stochastic fluctuations of magnetic dipole–dipole interactions between pairs of nuclei, while dielectric relaxation is a fingerprint of reorientation of the electric dipole moment of a. In this work these methods are exploited to enquire into dynamical properties of solid proteins

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