Laboratoire de Dynamique et Structure des Matériaux Moléculaires, UMR CNRS 8024, Université Lille I, 59655 Villeneuve d'Ascq Cedex, France.
J Chem Phys. 2009 Dec 28;131(24):245103. doi: 10.1063/1.3273218.
The low-frequency (omega<400 cm(-1)) vibrational properties of lysozyme in aqueous solutions of three well-known protecting sugars, namely, trehalose, maltose, and sucrose, have been investigated by means of complementary Raman scattering experiments and molecular dynamics simulations. The comparison of the Raman susceptibility chi(")(omega) of lysozyme/water and lysozyme/sugar/water solutions at a concentration of 40 wt % with the chi(") of dry lysozyme suggests that the protein dynamics mostly appears in the broad peak around 60-80 cm(-1) that reflects the vibrations experienced by atoms within the cage formed by their neighbors, whereas the broad shoulder around 170 cm(-1) mainly stems from the intermolecular O-H...O stretching vibrations of water. The addition of sugars essentially induces a significant high frequency shift and intensity reduction of this band that reveal a slowing down of water dynamics and a distortion of the tetrahedral hydrogen bond network of water, respectively. Furthermore, the lysozyme vibrational densities of states (VDOS) have been determined from simulations of lysozyme in 37-60 wt % disaccharide aqueous solutions. They exhibit an additional broad peak around 290 cm(-1), in line with the VDOS of globular proteins obtained in neutron scattering experiments. The influence of sugars on the computed VDOS mostly appears on the first peak as a slight high-frequency shift and intensity reduction in the low-frequency range (omega<50 cm(-1)), which increase with the sugar concentration and with the exposition of protein residues to the solvent. These results suggest that sugars stiffen the environment experienced by lysozyme atoms, thereby counteracting the softening of protein vibrational modes upon denaturation, observed at high temperature in the Raman susceptibility of the lysozyme/water solution and in the computed VDOS of unfolded lysozyme in water. Finally, the Raman susceptibility of sugar/water solutions and the calculated VDOS of water in the different lysozyme solutions confirm that sugars induce a significant strengthening of the hydrogen bond network of water that may stabilize proteins at high temperatures.
在三种著名保护糖（海藻糖、麦芽糖和蔗糖）的水溶液中，通过补充拉曼散射实验和分子动力学模拟，研究了溶菌酶的低频（ω<400cm(-1)）振动特性。在 40wt%浓度下，将溶菌酶/水和溶菌酶/糖/水溶液的拉曼磁化率 χ(")(ω)与干燥溶菌酶的 χ(")进行比较，表明蛋白质动力学主要出现在 60-80cm(-1)左右的宽峰中，该峰反映了原子在由其相邻原子形成的笼内的振动，而 170cm(-1)左右的宽肩主要源于水分子的 O-H...O 伸缩振动。添加糖会导致该带的高频位移和强度降低，分别揭示了水动力学的减慢和水的四面体氢键网络的扭曲。此外，还从溶菌酶在 37-60wt%二糖水溶液中的模拟中确定了溶菌酶的振动态密度（VDOS）。它们在 290cm(-1)左右表现出额外的宽峰，与在中子散射实验中获得的球状蛋白质的 VDOS 一致。糖对计算出的 VDOS 的影响主要表现在第一个峰值上，在低频范围内（ω<50cm(-1)）出现轻微的高频位移和强度降低，这一现象随着糖浓度和蛋白质残基对溶剂的暴露程度而增加。这些结果表明，糖使溶菌酶原子所处的环境变硬，从而抵消了在溶菌酶/水溶液的拉曼磁化率和水中展开的溶菌酶的计算 VDOS 中观察到的高温下蛋白质振动模式的软化。最后，糖/水溶液的拉曼磁化率和不同溶菌酶溶液中水的计算 VDOS 证实，糖会显著增强水的氢键网络，从而在高温下稳定蛋白质。
