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Role of the solvent in the dynamical transitions of proteins: The case of the lysozyme-water system
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View: Figures


Image of FIG. 1.
FIG. 1.

(a) OH stretch (OHS) bands, in the range, of lysozyme hydration water at hydration level , measured at different temperatures. As it can be observed their intensity increases by decreasing temperature; the three most intense ones correspond to a temperature below the FSC, whereas the three of lower intensity belong to the region in which protein denaturation takes place. (b) The deconvolution of the OHS spectra at , 220, 290, and . In all the figures, dots represent the experimental data, and the solid lines are the best fits. The dotted and dashed lines are the contributions to OHS oscillators from the low-density water (LDL) and the hydrogen-bonded molecules (HB), respectively. The dash-dot-dot lines indicate the spectral contributions of the non-hydrogen-bonded molecules (NHB). The dotted line refers to component III centered at , and the dashed line to component I centered at .

Image of FIG. 2.
FIG. 2.

(a) Relative integrated areas of the three FTIR components at three different lysozyme hydration levels, , 0.37, and 0.48. Squares indicate the fractional contribution of component I at , circles the fractional contribution of component III (“LDL”) at , and triangles the non-hydrogen-bonded (NHB) water. The three different regions of lysozyme behavior are also indicated, namely, native, reversible unfolding, and irreversible denaturation. Arrows show the temperature of maximum specific heat (Ref. 13) and the FSC crossover temperature . As one can see, the NHB and HB relative areas cross just near . (b) The inverse of the NMR self-diffusion coefficient of lysozyme hydration water as a function of 1/T (circles). Squares represent the values measured in bulk water. In the native region, of both bulk water and lysozyme hydration water obeys to a VFT law, but the protein hydration water displays a transition to an Arrhenius behavior at the FSC temperature . The location of this crossover temperature agrees with earlier neutron scattering experiments (Ref. 25) giving the temperature at which the protein looses its function. At a higher temperature , where the denaturation process of the protein takes place, the NMR self-diffusion data also show a second dynamical transition of hydration water.

Image of FIG. 3.
FIG. 3.

NMR longitudinal (spin-lattice) relaxation time , as a function of , for temperatures above and below the region of protein denaturation. Triangles correspond to bulk water, squares to protein hydration water, and circles to protons in the protein. Also for such a dynamical parameter, dramatic changes in the case of hydration water and protein protons may be observed within the denaturation temperature region.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Role of the solvent in the dynamical transitions of proteins: The case of the lysozyme-water system