Protein backbone fluctuations and NMR field-cycling relaxation spectroscopy

Abstract

Proton and deuteron field-cycling relaxation spectroscopy has been employed for the characterization of fluctuations in proteins and in their hydration shells. The nature of the fluctuations is shown to be different. Deuteron relaxation dispersion of water in particular does not reflect the dynamics specific for protein backbones. Protein backbone fluctuations are characterized by simple power laws describing the overall frequency dependence of the spin-lattice relaxation time over several decades. The exponent changes at about 200 K from a constant value above this temperature to values decreasing with decreasing temperatures. This may be interpreted by a transition from ergodic to nonergodic behavior in the time scale of the experiments.

Proton Spin-Relaxation Induced by Localized Spin-Dynamical Coupling in Proteins And in Other Imperfectly Packed Solids

“…7). This maximal value is similar to those reported for dry proteins [9]. It makes sense that b achieves a minimal value of 0 in the extreme limit of self-avoiding chains for which d f = 5/3.…”

“…In consequence, it is easy to imagine that the protein structure fluctuates among these nearly isoenergetic states and also samples higher energy states less frequently. To approach a model for the nuclear spin relaxation, we assume that relatively rare defect structures occur where some portion of the structure becomes transiently more mobile [2,9,14]. We suppose This leads to the idea of a mobile defect hypothesis where such a structural defect diffuses around within the protein structure and permits such things as exchange of amide hydrogen atoms even though the site is buried well within the folded structure.…”

“…decreases below 200 K [9]. Finally we have compared our theory to the proton dispersion curve of solid polycarbonate (Fig.…”

Interpretation of 1H and 2H spin–lattice relaxation dispersions: Insights from molecular dynamics simulations of polymer melts

“…In this way, it is possible to observe the frequency dependence of the relaxation time, T 1 ðωÞ, providing access to spectral densities and correlation functions [8][9][10]. This possibility was used to characterize dynamical processes in supercooled or confined liquids, polymer melts, biological materials, and liquid crystals [9][10][11][12][13][14][15][16][17][18][19].…”

Water molecule contributions to proton spin–lattice relaxation in rotationally immobilized proteins

“…Previous MRD studies of dry proteins have shown that the relaxation is described by a power law in the Larmor frequency, $\frac{1}{T_1}=A{\omega }^{-b}$, where A and b are constants [5; 6; 7; 8; 9; 10]. The physical origin of the power law has been related to a spin-fracton relaxation mechanism [6; 11; 12; 13; 14; 15].…”