Dielectric and Calorimetric Studies of Hydrated Purple Membrane

Berntsen, Peter; Bergman, Rikard; Jansson, Helén; Weik, Martin H.; Swenson, Jan

doi:10.1529/biophysj.104.057208

Cited by 31 publications

(48 citation statements)

References 43 publications

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“…For process I in the water sample (also at hydration level h = 0.4 at low temperatures) the temperature dependence of process I is better described by the Arrhenius equation (Eq. (3)), where both the relaxation time and the activation energy obtained from the Arrhenius fit correspond well to interfacial water in other systems [19][20][21][22].…”

Section: Dielectric Spectroscopysupporting

confidence: 52%

Protein and solvent dynamics as studied by QENS and dielectric spectroscopy

Jansson

Bergman

Swenson

2006

Journal of Non-Crystalline Solids

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Section: Dielectric Spectroscopysupporting

confidence: 52%

Protein and solvent dynamics as studied by QENS and dielectric spectroscopy

Jansson

Bergman

Swenson

2006

Journal of Non-Crystalline Solids

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“…Evidence of a hydration water transition in PM at 200 K has also been provided by calorimetry, dielectric spectroscopy (47), and lamellar diffraction measurements (37). The diffraction measurements show that at 200 K, intermembrane water in the second hydration layers becomes mobile enough to move along distances of the order of 1 m, the size of the average membrane patch, on the time scale of several tens of minutes (37).…”

Section: Hydration Water and Membrane Msds As A Function Of Temperaturementioning

confidence: 87%

Coupling of protein and hydration-water dynamics in biological membranes

Wood

Plazanet

Gabel

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

155

174

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The dynamical coupling between proteins and their hydration water is important for the understanding of macromolecular function in a cellular context. In the case of membrane proteins, the environment is heterogeneous, composed of lipids and hydration water, and the dynamical coupling might be more complex than in the case of the extensively studied soluble proteins. Here, we examine the dynamical coupling between a biological membrane, the purple membrane (PM), and its hydration water by a combination of elastic incoherent neutron scattering, specific deuteration, and molecular dynamics simulations. Examining completely deuterated PM, hydrated in H2O, allowed the direct experimental exploration of water dynamics. The study of natural abundance PM in D2O focused on membrane dynamics. The temperature-dependence of atomic mean-square displacements shows inflections at 120 K and 260 K for the membrane and at 200 K and 260 K for the hydration water. Because transition temperatures are different for PM and hydration water, we conclude that ps-ns hydration water dynamics are not directly coupled to membrane motions on the same time scale at temperatures <260 K. Molecular-dynamics simulations of hydrated PM in the temperature range from 100 to 296 K revealed an onset of hydration-water translational diffusion at Ϸ200 K, but no transition in the PM at the same temperature. Our results suggest that, in contrast to soluble proteins, the dynamics of the membrane protein is not controlled by that of hydration water at temperatures <260 K. Lipid dynamics may have a stronger impact on membrane protein dynamics than hydration water. molecular dynamics simulations ͉ neutron spectroscopy ͉ dynamical transition ͉ purple membrane ͉ bacteriorhodopsin P roteins are animated by a multitude of motions occurring on various length and time scales. In a current model, a protein is not characterized by a single three dimensional structure but, rather, by a large number of conformations, so-called conformational substates, that interconvert via molecular motions (1). Natively unfolded proteins reflect this conformational heterogeneity to an extreme degree. The developing concept of a free-energy landscape has put some order into the complex world of protein motions (1). The energy landscape is a highdimensional space, in which each conformational substate is defined by the coordinates of all atoms in the protein. The energy landscape is organized in a hierarchy of levels; the top level containing only a few substates that interconvert by relatively slow large-scale movements (2). Each substate at this level contains, itself, a larger number of substates, separated by smaller barriers that are sampled by more rapid motions. At the third level, the number of substates becomes very large and the barriers very small, and motions at this level have been proposed to take place on the ps-ns time scale (2). Which of the motions on different levels are crucial for biological function and whether and how they are correlated with each other are chall...

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“…[3]), Td corresponds to the onset o f a glass transition Tg, although others [33] pointed out that TD and Tg have different physical origins. Additionally, it has been suggested that To is correlated to the onset o f biochem ical activities o f the m acrom olecule [25,[27][28][29]34]. Transition at T* is hydration level indepen dent [29], Some w orks [29,35] interpreted this transition as related to the therm al activation o f m ethyl groups rotation.…”

Section: Introductionmentioning

confidence: 99%

Unusual specific heat of almost dry L-cysteine and L-cystine amino acids

et al. 2015

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A detailed quantitative analysis of the specific heat in the 0.5- to 200-K temperature range for almost dry L-cysteine and its dimer, L-cystine, amino acids is presented. We report the occurrence of a sharp first-order transition at ∼76 K for L-cysteine associated with the thiol group ordering which was successfully modeled with the two-dimensional Ising model. We demonstrated that quantum rotors, two-level systems (TLS), Einstein oscillators, and acoustic phonons (the Debye model) are essential ingredients to correctly describe the overall experimental data. Our analysis pointed out the absence of the TLS contribution to the low temperature specific heat of L-cysteine. This result was similar to that found in other noncrystalline amorphous materials, e.g., amorphous silicon, low density amorphous water, and ultrastable glasses. L-cystine presented an unusual nonlinear acoustic dispersion relation ω(q)=vq0.95 and a Maxwell-Boltzmann-type distribution of tunneling barriers. The presence of Einstein oscillators with ΘE∼70 K was common in both systems and adequately modeled the boson peak contributions.

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Dielectric and Calorimetric Studies of Hydrated Purple Membrane

Cited by 31 publications

References 43 publications

Protein and solvent dynamics as studied by QENS and dielectric spectroscopy

Protein and solvent dynamics as studied by QENS and dielectric spectroscopy

Coupling of protein and hydration-water dynamics in biological membranes

Unusual specific heat of almost dry L-cysteine and L-cystine amino acids

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