Brovchenko I, Burri R R, Krukau A, Oleinikova A, Winter R
Physical Chemistry, Dortmund University of Technology, Otto-Hahn-Str. 6, Dortmund D-44227, Germany.
J Chem Phys. 2008 Nov 21;129(19):195101. doi: 10.1063/1.3012562.
Volumetric and conformational properties of the amyloid beta(1-42) peptide (Abeta(42)) are studied in relation to the properties of hydration water in a wide temperature range by computer simulations. The apparent volume of Abeta(42), which is the change in the total volume of the solution due to the presence of Abeta(42), shows a quite different temperature dependence below and above T approximately 320 K. The apparent thermal expansion coefficient alpha(app)(Abeta(42)) is about 1.5x10(-3) K(-1) at T<or=320 K and about 0.6x10(-3) K(-1) at T>320 K. By evaluation of the thermal expansivity of hydration water, the intrinsic expansivity of the biomolecule in liquid water was determined for the first time. The intrinsic thermal expansion coefficient of Abeta(42) is found to be negative: alpha(int)(Abeta(42)) approximately -0.8x10(-3) K(-1). The negative thermal expansion coefficient of Abeta(42) can be attributed to its rubberlike (entropic) elasticity and/or to a decreasing number of intrapeptide hydrogen bonds. Upon heating, Abeta(42) transforms from an extended chain with a significant content of alpha-helices to a compact coil with noticeable content of beta-structures. A hydrogen-bonded spanning network of hydration water envelops Abeta(42) homogeneously at low temperatures but breaks into an ensemble of small water clusters upon heating via a percolation transition, whose midpoint is close to the temperature, where the apparent volume of Abeta(42) changes its temperature behavior. The mutual relation between the volumetric properties of Abeta(42), its conformational properties, and the properties of the hydration water is discussed.
通过计算机模拟，研究了淀粉样β（1 - 42）肽（Aβ（42））的体积和构象性质与宽温度范围内水化水性质的关系。Aβ（42）的表观体积是由于Aβ（42）的存在导致溶液总体积的变化，在约320 K以下和以上表现出截然不同的温度依赖性。表观热膨胀系数α（app）（Aβ（42））在T≤320 K时约为1.5×10⁻³ K⁻¹，在T＞320 K时约为0.6×10⁻³ K⁻¹。通过评估水化水的热膨胀性，首次确定了液态水中生物分子的固有膨胀性。发现Aβ（42）的固有热膨胀系数为负：α（int）（Aβ（42））约为 - 0.8×10⁻³ K⁻¹。Aβ（42）的负热膨胀系数可归因于其橡胶状（熵）弹性和/或肽内氢键数量的减少。加热时，Aβ（42）从具有大量α - 螺旋的伸展链转变为具有明显β - 结构含量的紧密卷曲。在低温下，水化水的氢键跨越网络均匀地包裹着Aβ（42），但在加热时通过渗流转变分解为小水簇的集合，其转变中点接近Aβ（42）表观体积改变其温度行为的温度。讨论了Aβ（42）的体积性质、其构象性质与水化水性质之间的相互关系。
