Influence of Hydration on Protein Dynamics: Combining Dielectric and Neutron Scattering Spectroscopy Data

Abstract

Combining dielectric spectroscopy and neutron scattering data for hydrated lysozyme powders, we were able to identify several relaxation processes and follow protein dynamics at different hydration levels over a broad frequency and temperature range. We ascribe the main dielectric process to protein's structural relaxation coupled to hydration water and the slowest dielectric process to a larger scale protein's motions. Both relaxations exhibit a smooth, slightly super-Arrhenius temperature dependence between 300 and 180 K. The temperature dependence of the slowest process follows the main dielectric relaxation, emphasizing that the same friction mechanism might control both processes. No signs of a proposed sharp fragile-to-strong crossover at T approximately 220 K are observed in temperature dependences of these processes. Both processes show strong dependence on hydration: the main dielectric process slows down by six orders with a decrease in hydration from h approximately 0.37 (grams of water per grams of protein) to h approximately 0.05. The slowest process shows even stronger dependence on hydration. The third (fastest) dielectric relaxation process has been detected only in samples with high hydration ( h approximately 0.3 and higher). We ascribe it to a secondary relaxation of hydration water. The mechanism of the protein dynamic transition and a general picture of the protein dynamics are discussed.

Mean-squared atomic displacements in hydrated lysozyme, native and denatured

“…For example, it has been reported that the transition is coupled to the onset of translational motions in hydration water [47][48][49]. In addition, it has been debated whether the transition is a real phenomenon, or merely a manifestation of the fact that the measurable atomic dynamics enter the experimentally accessible resolution window above certain temperatures [17,18,24,25,27]. In such a scenario, the dynamic motions of the biomolecules may increase without any discontinuity.…”

Boson peak as a probe of quantum effects in a glassy state of biomolecules: The case of L-cysteine

“…[1][2][3][4][5][6] But, recently it has been suggested that it may be correlated to anharmonic and glass transitions observed at T D ∼ 180 − 200 K and T g ∼ 80 − 100 K, respectively. As pointed out by Khodadadi et al [7] both have different physical origin and should not be confused.…”

“…The BP presents similar thermal properties, as described in the literature. [7,20] Thus one could assign the low frequency band in the 20 − 60 cm −1 spectral window to the BP . The temperature dependence of the BP is better accomplished compensating normalizing the spectra by the Bose-Einstein occupation factor.…”

Dynamical changes in hydration water accompanying lysozyme thermal denaturation

“…Because we are focusing on the hydration water, we evaluate τ θ by considering the T 1s values and by assuming the constant values a = 1.38Å, b = 0.92Å, and r = 1.52Å [60]. Figure 3 compares the thermal behaviors of τ θ in lysozyme hydration water measured by NMR (h = 0.3), dielectric spectroscopy (h = 0.37) [24], and neutron scattering (h = 0.4) [25], with that of bulk water at ambient pressure [57] and emulsified water at 2 kbar [61]. Note that when the temperature drops below the temperature of irreversible denaturation, the reorientational correlation time in hydration water is slower than in bulk Fig.…”

“…Although this precise value of temperature has been debated, given the possibility of inadequate instrumental resolutions, there is a consensus that the crossover occurs and that it is important [21][22][23][24][25][26][27][28][29][30][31].…”