Quasielastic neutron scattering studies on couplings of protein and water dynamics in hydrated elastin

Abstract

Performing quasielastic neutron scattering measurements and analyzing both elastic and quasielasic contributions, we study protein and water dynamics of hydrated elastin. At low temperatures, hydration-independent methyl group rotation dominates the findings. It is characterized by a Gaussian distribution of activation energies centered at about Em = 0.17 eV. At ∼195 K, coupled protein–water motion sets in. The hydration water shows diffusive motion, which is described by a Gaussian distribution of activation energies with Em = 0.57 eV. This Arrhenius behavior of water diffusion is consistent with previous results for water reorientation, but at variance with a fragile-to-strong crossover at ∼225 K. The hydration-related elastin backbone motion is localized and can be attributed to the cage rattling motion. We speculate that its onset at ∼195 K is related to a secondary glass transition, which occurs when a β relaxation of the protein has a correlation time of τβ ∼ 100 s. Moreover, we show that its temperature-dependent amplitude has a crossover at the regular glass transition Tg = 320 K of hydrated elastin, where the α relaxation of the protein obeys τα ∼ 100 s. By contrast, we do not observe a protein dynamical transition when water dynamics enters the experimental time window at ∼240 K.

Confinement Effects on Glass-Forming Aqueous Dimethyl Sulfoxide Solutions

“…The BDS findings for the ficoll and lysozyme matrices differed in an even slower process III with a very high dielectric relaxation strength, which existed in the latter but not in the former confinement, see insets in Figure 1 . A similar BDS process was reported in previous studies on various hydrated proteins [ 68 , 71 , 72 ], but its origin is still a matter of debate [ 73 , 74 , 75 ].…”

“…Therefore, we refrain from a more detailed analysis. Process III is singular to the lysozyme mixtures, in accordance with the conjecture that it is related to solvation-enabled protein dynamics [ 73 , 74 , 75 ]. It has a weaker temperature dependence than the faster processes.…”

Evidence for an Ordering Transition near 120 K in an Intrinsically Disordered Protein, Casein

“…Further, interaction of free fatty acids with proteins [ 24 ] and interaction of sugars with biological membranes [ 25 ] was investigated. Stochastic molecular librations are sensitive to a so-called dynamical transition in proteins and in other biological systems [ 16 , 19 , 26 , 27 , 28 ], which is known occur between 170 and 220 K from numerous neutron-scattering experiments and MD simulations to—see e.g., [ 29 , 30 , 31 ] for recent references. Note however that the nature of this transition is still heavily debated.…”

Mobility of bound water in PNIPAM microgels

“…The time scale of the MSD corresponds to the time scale provided by the resolution of the instrument and is C2 ns in the case of the backscattering spectrometer SPHERES. 25 The MSD is plotted up to 270 K, avoiding discontinuity of I(q) at 273 K in the hydrated sample. The MSD up to this point is of the order of o0.6 Å 2 .…”

“…For the hydrated sample, the fitted hu 2 i at low q deviates from the large q behavior, as it has been observed also for hydrated elastin. 25 Fig. 3 shows therefore the high-q fit of the MSD.…”