The emergence of very high NMR magnetic fields will certainly encourage the study of larger biological systems with their dynamics and interactions. NMR spin relaxation allows to probe the dynamic properties of proteins where the longitudinal (R1) and transverse (R2) relaxation rates of 15N, in addition to the heteronuclear 1H-15N NOE, describe the ps-ns time scale. Their analytical representation involves the chemical shift anisotropy (CSA) effect which represents the major contribution at a very high magnetic field above 18,8 T. An accurate analysis of these latter parameters in terms of free model (FM) requires the consideration of its effect. So far, a uniform value of -160 ppm for CSA has been widely used to derive the backbone order parameters (S2), giving rise to a large fluctuation of its value at very high magnetic fields. Conversely, the use of site-specific CSA improves the accurate analysis of protein dynamics but requires a cost-effective multi-field experimental approach. In this paper, we show how CSA contributes mainly to the relaxation parameters at 28,2 T compared to lower magnetic fields and can confound the determination of S2. We propose to replace the tedious measurement of spin relaxation at multiple fields with a combination of molecular dynamics (MD) and the measurement of spin relaxation at a single very high magnetic field. We applied this strategy to three well-folded proteins (ubiquitin, GB3, and ribonuclease H) to show that the determined order parameters are in good agreement with those obtained using experimental data alone.

DOI: 10.1039/d4cp03821e

Platform: IMEC-ISB-UCCS