Structural Biology Brussels, Flanders Interuniversity Institute for Biotechnology, and Vrije Universiteit Brussel, 1050 Elsene, Belgium.
Proc Natl Acad Sci U S A. 2014 Feb 4;111(5):E546-53. doi: 10.1073/pnas.1309320111. Epub 2014 Jan 21.
The development of multistep nucleation theory has spurred on experimentalists to find intermediate metastable states that are relevant to the solidification pathway of the molecule under interest. A great deal of studies focused on characterizing the so-called "precritical clusters" that may arise in the precipitation process. However, in macromolecular systems, the role that these clusters might play in the nucleation process and in the second stage of the precipitation process, i.e., growth, remains to a great extent unknown. Therefore, using biological macromolecules as a model system, we have studied the mesoscopic intermediate, the solid end state, and the relationship that exists between them. We present experimental evidence that these clusters are liquid-like and stable with respect to the parent liquid and metastable compared with the emerging crystalline phase. The presence of these clusters in the bulk liquid is associated with a nonclassical mechanism of crystal growth and can trigger a self-purifying cascade of impurity-poisoned crystal surfaces. These observations demonstrate that there exists a nontrivial connection between the growth of the macroscopic crystalline phase and the mesoscopic intermediate which should not be ignored. On the other hand, our experimental data also show that clusters existing in protein solutions can significantly increase the nucleation rate and therefore play a relevant role in the nucleation process.
多步成核理论的发展促使实验人员寻找与感兴趣分子的凝固途径相关的中间亚稳态。大量研究集中于表征在沉淀过程中可能出现的所谓“临界前簇”。然而，在高分子体系中，这些簇在成核过程以及沉淀过程的第二阶段（即生长）中可能发挥的作用在很大程度上仍不清楚。因此，我们使用生物大分子作为模型体系，研究了介观中间态、固态终态以及它们之间的关系。我们提供了实验证据表明，这些簇类似于液体，与母体液体相比是稳定的，与新兴的结晶相相比是亚稳的。这些簇在本体液体中的存在与非经典的晶体生长机制相关，并可能引发受杂质污染的晶体表面的自净化级联。这些观察结果表明，宏观结晶相的生长与介观中间态之间存在着不容忽视的复杂联系。另一方面，我们的实验数据还表明，存在于蛋白质溶液中的簇可以显著提高成核速率，因此在成核过程中发挥着相关作用。
