Capaccioli Simone, Zheng Lirong, Kyritsis Apostolos, Paciaroni Alessandro, Vogel Michael, Ngai Kia L
Dipartimento di Fisica, Università di Pisa, Largo Bruno Pontecorvo 3, I-56127 Pisa, Italy.
CNR-IPCF, Largo Bruno Pontecorvo 3, I-56127 Pisa, Italy.
ACS Omega. 2020 Dec 23;6(1):340-347. doi: 10.1021/acsomega.0c04655. eCollection 2021 Jan 12.
Customarily, the studies of dynamics of hydrated proteins are focused on the fast hydration water ν-relaxation, the slow structural α-relaxation responsible for a single glass transition, and the protein dynamic transition (PDT). Guided by the analogy with the dynamics of highly asymmetric mixtures of molecular glass-formers, we explore the possibility that the dynamics of hydrated proteins are richer than presently known. By providing neutron scattering, dielectric relaxation, calorimetry, and deuteron NMR data in two hydrated globular proteins, myoglobin and BSA, and the fibrous elastin, we show the presence of two structural α-relaxations, α1 and α2, and the hydration water ν-relaxation, all coupled together with interconnecting properties. There are two glass transition temperatures and corresponding to vitrification of the α1 and α2 processes. Relaxation time τ() of the α2-relaxation changes its Arrhenius temperature dependence to super-Arrhenius on crossing from below. The ν-relaxation responds to the two vitrifications by changing the -dependence of its relaxation time τ() on crossing consecutively and . It generates the PDT at where τ( ) matches about five times the experimental instrument timescale τ, provided that > . This condition is satisfied by the hydrated globular proteins considered in this paper, and the ν-relaxation is in the liquid state with τ() having the super-Arrhenius temperature dependence. However, if < , the ν-relaxation fails to generate the PDT because it is in the glassy state and τ() has Arrhenius -dependence, as in the case of hydrated elastin. Overall, the dynamics of hydrated proteins are the same as the dynamics of highly asymmetric mixtures of glass-formers. The results from this study have expanded the knowledge of the dynamic processes and their properties in hydrated proteins, and impact on research in this area is expected.
通常，对水合蛋白质动力学的研究集中在快速水合水ν弛豫、负责单一玻璃化转变的缓慢结构α弛豫以及蛋白质动力学转变（PDT）上。在与分子玻璃形成剂的高度不对称混合物的动力学类比的指导下，我们探讨了水合蛋白质的动力学比目前已知的更丰富的可能性。通过提供两种水合球状蛋白质（肌红蛋白和牛血清白蛋白）以及纤维状弹性蛋白的中子散射、介电弛豫、量热法和氘核磁共振数据，我们展示了两种结构α弛豫（α1和α2）以及水合水ν弛豫的存在，它们都通过相互连接的性质耦合在一起。存在两个玻璃化转变温度 和 ，分别对应于α1和α2过程的玻璃化。α2弛豫的弛豫时间τ()在从下方穿过 时，其阿仑尼乌斯温度依赖性变为超阿仑尼乌斯。ν弛豫通过在连续穿过 和 时改变其弛豫时间τ()的 -依赖性来响应这两种玻璃化。如果 > ，它在 处产生PDT，此时τ( )约为实验仪器时间尺度τ的五倍。本文中考虑的水合球状蛋白质满足此条件，并且ν弛豫处于液态，τ()具有超阿仑尼乌斯温度依赖性。然而，如果 < ，ν弛豫无法产生PDT，因为它处于玻璃态且τ()具有阿仑尼乌斯 -依赖性，就像水合弹性蛋白的情况一样。总体而言，水合蛋白质的动力学与玻璃形成剂的高度不对称混合物的动力学相同。这项研究的结果扩展了对水合蛋白质中动态过程及其性质的认识，预计将对该领域的研究产生影响。
