Peptide and Protein Dynamics and Low-Temperature/DNP Magic Angle Spinning NMR.

In DNP MAS NMR experiments at ∼80-110 K, the structurally important -CH and -NH signals in MAS spectra of biological samples disappear due to the interference of the molecular motions with the H decoupling. Here we investigate the effect of these dynamic processes on the NMR line shapes and signal intensities in several typical systems: (1) microcrystalline APG, (2) membrane protein bR, (3) amyloid fibrils PI3-SH3, (4) monomeric alanine-CD, and (5) the protonated and deuterated dipeptide N-Ac-VL over 78-300 K. In APG, the three-site hopping of the Ala-C peak disappears completely at 112 K, concomitant with the attenuation of CP signals from other C's and N's. Similarly, the N signal from Ala-NH disappears at ∼173 K, concurrent with the attenuation in CP experiments of other N's as well as C's. In bR and PI3-SH3, the methyl groups are attenuated at ∼95 K, while all other C's remain unaffected. However, both systems exhibit substantial losses of intensity at ∼243 K. Finally, with spectra of Ala and N-Ac-VL, we show that it is possible to extract site specific dynamic data from the temperature dependence of the intensity losses. Furthermore, H labeling can assist with recovering the spectral intensity. Thus, our study provides insight into the dynamic behavior of biological systems over a wide range of temperatures, and serves as a guide to optimizing the sensitivity and resolution of structural data in low temperature DNP MAS NMR spectra.