Zanatta Marco, Tavagnacco Letizia, Buratti Elena, Bertoldo Monica, Natali Francesca, Chiessi Ester, Orecchini Andrea, Zaccarelli Emanuela
Department of Computer Science, University of Verona, Strada le Grazie 15, 37134 Verona, Italy.
Consiglio Nazionale delle Ricerche (CNR)-Istituto dei Sistemi Complessi, Sede Sapienza, and Department of Physics, Sapienza University of Rome, Piazzale A. Moro 2, 00185 Rome, Italy.
Sci Adv. 2018 Sep 28;4(9):eaat5895. doi: 10.1126/sciadv.aat5895. eCollection 2018 Sep.
A low-temperature dynamical transition has been reported in several proteins. We provide the first observation of a "protein-like" dynamical transition in nonbiological aqueous environments. To this aim, we exploit the popular colloidal system of poly--isopropylacrylamide (PNIPAM) microgels, extending their investigation to unprecedentedly high concentrations. Owing to the heterogeneous architecture of the microgels, water crystallization is avoided in concentrated samples, allowing us to monitor atomic dynamics at low temperatures. By elastic incoherent neutron scattering and molecular dynamics simulations, we find that a dynamical transition occurs at a temperature ~ 250 K, independently from PNIPAM mass fraction. However, the transition is smeared out on approaching dry conditions. The quantitative agreement between experiments and simulations provides evidence that the transition occurs simultaneously for PNIPAM and water dynamics. The similarity of these results with hydrated protein powders suggests that the dynamical transition is a generic feature in complex macromolecular systems, independently from their biological function.
已有报道称几种蛋白质中存在低温动力学转变。我们首次观察到在非生物水性环境中存在“类蛋白质”动力学转变。为此，我们利用了常见的聚异丙基丙烯酰胺（PNIPAM）微凝胶胶体系统，将其研究扩展到前所未有的高浓度。由于微凝胶的非均匀结构，在浓缩样品中避免了水结晶，这使我们能够在低温下监测原子动力学。通过弹性非相干中子散射和分子动力学模拟，我们发现动力学转变发生在约250 K的温度下，与PNIPAM质量分数无关。然而，在接近干燥条件时，转变变得模糊。实验与模拟之间的定量一致性证明，PNIPAM和水的动力学同时发生转变。这些结果与水合蛋白质粉末的相似性表明，动力学转变是复杂大分子系统中的一个普遍特征，与它们的生物学功能无关。
