Solvent dependence of dynamic transitions in protein solutions (original) (raw)
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Temperature and timescale dependence of protein dynamics in methanol : water mixtures
Physical Chemistry Chemical Physics, 2005
Experimental and computer simulation studies have suggested the presence of a transition in the dynamics of hydrated proteins at around 180-220 K. This transition is manifested by nonlinear behaviour in the temperature dependence of the average atomic mean-square displacement which increases at high temperature. Here, we present results of a dynamic neutron scattering analysis of the transition for a simple enzyme: xylanase in water : methanol solutions of varying methanol concentrations. In order to investigate motions on different timescales, two different instruments were used: one sensitive to B100 ps timescale motions and the other to Bns timescale motions. The results reveal distinctly different behaviour on the two timescales examined. On the shorter timescale the dynamics are dictated by the properties of the surrounding solvent: the temperature of the dynamical transition lowers with increasing methanol concentration closely following the melting behaviour of the corresponding water : methanol solution. This contrasts with the longer (ns) timescale results in which the dynamical transition appears at temperatures lower than the corresponding melting point of the cryosolvent. These results are suggested to arise from a collaborative effect between the protein surface and the solvent which lowers the effective melting temperature of the protein hydration layer. Taken together, the results suggest that the protein solvation shell may play a major role in the temperature dependence of protein solution dynamics.
Spectroscopy, 2010
This review article describes our neutron scattering experiments made in the past four years for the understanding of the single-particle (hydrogen atom) dynamics of a protein and its hydration water and the strong coupling between them. We found that the key to this strong coupling is the existence of a fragile-to-strong dynamic crossover (FSC) phenomenon occurring at around T L = 225 ± 5 K in the hydration water. On lowering of the temperature toward FSC, the structure of hydration water makes a transition from predominantly the high density form (HDL), a more fluid state, to predominantly the low density form (LDL), a less fluid state, derived from the existence of a liquid-liquid critical point at an elevated pressure. We show experimentally that this sudden switch in the mobility of hydration water on Lysozyme, B-DNA and RNA triggers the dynamic transition, at a temperature T D = 220 K, for these biopolymers. In the glassy state, below T D , the biopolymers lose their vital conformational flexibility resulting in a substantial diminishing of their biological functions. We also performed molecular dynamics (MD) simulations on a realistic model of hydrated lysozyme powder, which confirms the existence of the FSC and the hydration level dependence of the FSC temperature. Furthermore, we show a striking feature in the short time relaxation (β-relaxation) of protein dynamics, which is the logarithmic decay spanning 3 decades (from ps to ns). The long time α-relaxation shows instead a diffusive behavior, which supports the liquid-like motions of protein constituents. We then discuss our recent high-resolution X-ray inelastic scattering studies of globular proteins, Lysozyme and Bovine Serum Albumin. We were able to measure the dispersion relations of collective, intra-protein phonon-like excitations in these proteins for the first time. We found that the phonon energies show a marked softening and at the same time their population increases substantially in a certain wave vector range when temperature crosses over the T D . Thus the increase of biological activities above T D has positive correlation with activation of slower and large amplitude collective motions of a protein.
Temperature dependence of protein dynamics as affected by sugars: a neutron scattering study
2007
Neutron scattering data on lysozyme-trehalose and lysozyme-sucrose aqueous mixtures, and on trehalose and sucrose aqueous mixtures are presented for a wide temperature range. Although the degree of protein coupling to solvent seems to be an open question in the literature, we present evidence that seems to be a firm link between a local dynamics of the protein with that of the glassy host. One of the objectives of this study was to explore the relationship between protein dynamics and glassy host. Measuring the <u 2 > of lysozyme mixtures, we arrive at a qualitative description of how their thermal stability is affected by the presence of two sugars at different temperatures. Whereas the Q dependence of the elastic incoherent structure factor gives information about the geometry and the amplitudes of the motions.
1995
The incoherent quasi-elastic neutron scattering (IQNS) method is a useful technique to study biomolecular dynamics. The versatility of the method makes possible motional studies of biomolecules in different forms: powder, crystal, and solution; and at different temperatures. Thus, it allows for the investigation of biomolecular dynamics over a wide-range of physical conditions. We have used the IQNS method to study the motions of side chains in trypsin and myoglobin at various D_2O hydration levels. The scattering spectra S(Q, omega) were measured in constant-Q mode. The protein in powder form exhibits vibrational high-frequency motions, while the protein in solution and in crystals are characterized by diffusive jumps, and high-frequency vibrations. At temperatures below 200K, the S(Q, omega) for these proteins in solution is similar to an harmonic solid. As temperature increases, a transition is seen at 200K, above which the protein becomes more liquid -like with rapid transitions between conformational substates. The diffusion constant D for the side chains is on the order of 10^{-6} cm ^2/sec.
Protein and solvent dynamics: How strongly are they coupled?
The Journal of Chemical Physics, 2004
Analysis of Raman and neutron scattering spectra of lysozyme demonstrates that the protein dynamics follow the dynamics of the solvents glycerol and trehalose over the entire temperature range measured 100-350 K. The protein's fast conformational fluctuations and low-frequency vibrations and their temperature variations are very sensitive to behavior of the solvents. Our results give insight into previous counterintuitive observations that protein relaxation is stronger in solid trehalose than in liquid glycerol. They also provide insight into the effectiveness of glycerol as a biological cryopreservant.
The Journal of Chemical Physics, 2009
In this quasielastic neutron scattering ͑QENS͒ study we have investigated the relation between protein and solvent dynamics. Myoglobin in different water:glycerol mixtures has been studied in the temperature range of 260-320 K. In order to distinguish between solvent and protein dynamics we have measured protonated as well as partly deuterated samples. As commonly observed for bulk as well as for confined water, the dynamics of the surrounding solvent is well described by a jump diffusion model. The intermediate scattering function I͑Q , t͒ from the protein ͑partly deuterated samples͒ was analyzed by fitting a single Kohlrausch-Williams-Watts ͑KWW͒ stretched exponential function to the data. However, due to the limited experimental time window, two different curve fitting approaches were used. The first one was performed with the assumption that I͑Q , t͒ decays to zero at long times, i.e., it was assumed that all protein relaxations that are observed on the experimental time scale, as well as would be observed on longer time scales, can be described by a single KWW function. In the second approach we instead assumed that both the protein relaxation time p and the stretching parameter  KWW were Q-independent, i.e., we assumed that the protein dynamics is dominated by more local motions. Advantages and disadvantages of both approaches are discussed. The first approach appears to work best at higher Q-values, indicating a power law relation of the Q-dependent protein dynamics for all samples and temperatures, whereas the second approach seems to work at lower Q-values, where the expected confined diffusion of hydrogen atoms in the protein gives the assumed Q-independent relaxation time. Independent of the chosen approach we find a significant correlation between the average relaxation time of the protein and the diffusion constant ͑or in this case the related relaxation time͒ of the solvent. However, the correlation is not perfect since the average relaxation time of the protein is more strongly dependent on the total amount of solvent than the diffusion constant of the solvent itself. Thus, the average relaxation time of the protein decreases not only with increasing solvent mobility, but also with increasing solvent content.
Protein dynamics studied by neutron scattering
Quarterly Reviews of Biophysics, 2002
1. Introduction 3282. Basic concepts of neutron scattering 3292.1 Introduction 3292.2 Neutron-scattering functions 3312.3 Coherent and incoherent neutron scattering. The particular role of hydrogen in incoherent scattering 3322.4 Total elastic scattering, EISF and mean square displacement (MSD) 3332.5 Quasielastic scattering and relaxation function 3342.6 Inelastic scattering and density of states 3353. Experimental aspects and instruments 3353.1 Energy and space resolution 3353.2 General sample aspects 3353.3 Potential effects of D2O on dynamics 3363.4 Experimental 2H (deuterium) labelling 3364. Physics of protein dynamics 3364.1 Models 3364.2 The dynamical transition 3384.3 Effective force constants 3395. Dynamics of hydrated protein powders 3395.1 First experiments on myoglobin 3405.2 Dynamical transitions in other proteins 3405.3 The role of hydration water 3415.4 Influence of the solvent 3445.5 Diffusional motions within proteins by QENS 3465.6 Inelastic neutron scattering and ...
Dynamics of Protein and its Hydration Water: Neutron Scattering Studies on Fully Deuterated GFP
Biophysical Journal, 2012
We present a detailed analysis of the picosecond-to-nanosecond motions of green fluorescent protein (GFP) and its hydration water using neutron scattering spectroscopy and hydrogen/deuterium contrast. The analysis reveals that hydration water suppresses protein motions at lower temperatures (<~200 K), and facilitates protein dynamics at high temperatures. Experimental data demonstrate that the hydration water is harmonic at temperatures <~180-190 K and is not affected by the proteins' methyl group rotations. The dynamics of the hydration water exhibits changes at~180-190 K that we ascribe to the glass transition in the hydrated protein. Our results confirm significant differences in the dynamics of protein and its hydration water at high temperatures: on the picosecond-to-nanosecond timescale, the hydration water exhibits diffusive dynamics, while the protein motions are localized to <~3 Å. The diffusion of the GFP hydration water is similar to the behavior of hydration water previously observed for other proteins. Comparison with other globular proteins (e.g., lysozyme) reveals that on the timescale of 1 ns and at equivalent hydration level, GFP dynamics (mean-square displacements and quasielastic intensity) are of much smaller amplitude. Moreover, the suppression of the protein dynamics by the hydration water at low temperatures appears to be stronger in GFP than in other globular proteins. We ascribe this observation to the barrellike structure of GFP.
Internal motions in proteins: A combined neutron scattering and molecular modelling approach
Pramana, 2004
It is well-known that water plays a major role in the stability and catalytic function of proteins. Both the effect of hydration water on the dynamics of proteins and that of proteins on the dynamics of water have been studied using inelastic neutron scattering. Inelastic neutron scattering is the most direct probe of diffusive protein dynamics on the picosecond-nanosecond time-scale. We present here results relative to a photosynthetic globular protein, the C-phycocyanin, that can be obtained in protonated and deuterated forms. Diffusive motions have been studied using the protonated C-phycocyanin, protein. Molecular dynamics simulation and analytical theory have been combined to analyse the data and get a detailed description of diffusive motions for protein. The simulation-derived dynamic structure factors are in good agreement with experiment. The dynamical parameters are shown to present a smooth variation with distance from the core of the protein.