Direct Experimental Characterization of Contributions from Self-Motion of Hydrogen and from Interatomic Motion of Heavy Atoms to Protein Anharmonicity

Abstract

One fundamental challenge in biophysics is to understand the connection between protein dynamics and its function. Part of the difficulty arises from the fact that proteins often present local atomic motions and collective dynamics on the same time scales, and challenge the experimental identification and quantification of different dynamic modes. Here, by taking lyophilized proteins as the example, we combined deuteration technique and neutron scattering to separate and characterize the self-motion of hydrogen and the collective interatomic motion of heavy atoms (C, O, N) in proteins on the pico-to-nanosecond time scales. We found that hydrogen atoms present an instrument-resolution-dependent onset for anharmonic motions, which can be ascribed to the thermal activation of local sidegroup motions. However, the protein heavy atoms exhibit an instrument-resolutionindependent anharmonicity around 200 K, which results from unfreezing of the relaxation of the protein structures on the laboratory equilibrium time (100−1000 s), softening of the entire bio-macromolecules.

Heterogeneity of Water Molecules on the Free Surface of Thin Reduced Graphene Oxide Sheets

“…Such resolution-dependent behavior demonstrates that water remains in the liquid state at ∼190 K (−80 °C), rather than turning into solid, as the liquid−solid transition is a critical phenomenon, whose characteristic temperature should be resolution independent. 41 As illustrated in Figure S4, this noncrystallizable water, which is free of hysteresis, is present in all samples independent of hydration levels. When increasing h to 0.2, an unambiguous thermal hysteresis (heating−cooling gap) appears in S(q,Δt) starting around 230 K (Figure 2b).…”

“…To address this question, one can examine the temperature dependence of S(q,Δt) using neutron instruments with distinct resolution time, Δt. 41 As shown in Figure 2f, S(q,Δt) at h = 0.1 bends downward at ∼190 K, as measured using the neutron instrument with Δt = 1 ns, indicating the thermal activation of a relaxation process in the water molecules. However, when we measured the same sample using a different instrument with a distinct resolution of Δt = 80 ps, the activation temperature drastically shifts to ∼240 K (Figure 2f).…”

“…The intriguing question is whether this water turns to amorphous ice at the low temperature or remains in liquid state. To address this question, one can examine the temperature dependence of S ( q ,Δ t ) using neutron instruments with distinct resolution time, Δ t . As shown in Figure f, S ( q ,Δ t ) at h = 0.1 bends downward at ∼190 K, as measured using the neutron instrument with Δ t = 1 ns, indicating the thermal activation of a relaxation process in the water molecules.…”

“…However, when we measured the same sample using a different instrument with a distinct resolution of Δ t = 80 ps, the activation temperature drastically shifts to ∼240 K (Figure f). Such resolution-dependent behavior demonstrates that water remains in the liquid state at ∼190 K (−80 °C), rather than turning into solid, as the liquid–solid transition is a critical phenomenon, whose characteristic temperature should be resolution independent …”

Absolutely necessary to consider the caged dynamics and the JGX β-relaxation in solving the glass transition problem

“…In several papers we reported our analyses of the published data to show in many different glass-formers that the intensity of the caged dynamics exhibits a two-step increase at T gβ and T g . The phenomenon is general and found in polyalcohols [44], pharmaceuticals [44], many amorphous polymers [45], several small molecular van der Waals glass-formers [46,47], metallic glass [48], carbohydrates [49], and proteins [50,51]. In some cases, T gβ was determined directly by calorimetry, positronium annihilation lifetime spectroscopy (PALS).…”