科研之友
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摘要
Cold- and heat-induced beta-lactoglobulin (BLG) transformations have been analyzed in the presence of 4 M urea, from Raman spectroscopy investigations carried out simultaneously in the low wavenumber range (10400 cm-1) and in the amide I region (15001800 cm-1). These investigations show common features between the denaturation processes at low and high temperatures. The denatured states are reached via an intermediate state characterized by a soft tertiary structure without detectable conformational changes. This intermediate is intimately connected with a tetrahedral hydrogen-bond structure of water which extends over a limited range. It is shown that the disruption of the hydrogen-bond network of D2O has an important consequence on the solvent dynamics, which controls protein dynamics and is characterized by an anharmonic behavior. By monitoring the amide I mode, conformational changes are detected at low temperature (below 5 degrees C) and determined to be similar to those detected at high temperature in the presence of urea near 65 degrees C, and in the absence of urea near 80 degrees C. The conformational changes are described as a loss of a-helix structures and a concomitant formation of beta-sheets. The temperature dependence of the amide I wavenumber in BLG dissolved in the 4 M urea aqueous solution was interpreted on the basis of a two-state model, leading to the protein stability curve related to its molecular conformation.
- 出版日期2012-1
