| Popis: |
Trehalose, a non-reducing disaccharide of glucose, has a peculiar efficacy in the preservation of isolated proteins, membranes and tissues (1). A number of experimental techniques, sensitive to atomic motions, and molecular dynamics simulations (MD) have shown that, in heme proteins embedded in trehalose matrices, the large-scale internal motions, which in glycerol-water start above ~ 180 K, are strongly inhibited. Such inhibition increases when the water content is decreased. Furthermore, FTIR spectroscopy and MD results enabled to infer the existence of water molecules at the protein interface involved in hydrogen bond networks, which anchor the protein to the surrounding water-trehalose matrix and couple the internal degrees of freedom of the protein to those of the external water-sugar matrix (2 and references therein). This tight dynamical and structural coupling has been investigated in samples of reduced horse heart cytochrome (cyt) c, in water glycerol solution and embedded in a trehalose matrix, which was led to extreme drought, but still contained traces of residual water. We performed Fe K-edge X-ray absorption spectroscopy measurements at liquid nitrogen and at room temperature. Since the EXAFS function is damped by an exponential term, which contains the mean square relative displacement, information on thermal fluctuations and static disorder can be obtained. Our measurements evidenced that, while lowering the temperature from 300 K to 77 K does not significatively alter the EXAFS signal both in the water-glycerol solution and in the trehalose-water matrix, large differences are observed between the spectra in the two different environments. In particular the damping of the EXAFS function is dramatically decreased in the trehalose-water matrix as compared to the water-glycerol mixture. This indicates that the trehalose-water matrix drastically alters the protein energy landscape, most likely hindering the protein internal dynamics and promoting only some conformational substates at the level of local structure. |
